Role of sensor in color rendering?

[Siobhan_K]

. . . was made for you.

as jim and others have pointed out, raw conversion methodology and practice matters, here--possibly more than any other factor, including sensor cfa design.

if you are so serious--and particular--about your color that you are measuring and designing your own sensor profiles, that you are measuring white balance for black-body-radiation "accuracy" rather than for personal preference, then clearly it's time to become at least that much involved, conversant, skilled in your raw conversion methodology.

if you're concerned about hue variation over skin tones (or any color region) in your raw conversion, capture one is the converter you need to be using. because it offers the ability to edit hue, saturation, and luminance uniformity for any hue-saturation-luminance region you select. and it's not a major edit. it's easy, it's fast. you drop your mouse on the skin tone you want, you push the hue variation slider to lessen that hue region's degree of "drift" toward red or green over any breadth of saturation and luminance you'd like.

take a look.

Hello!

Thanks for your feedback.

I certainly do not pretend to have any particular skill with Capture One Pro, but I used to use it and I'm quite familiar with their colors tool. I can only agree: it's excellent!

I gave a try to version 20 of Capture One Pro recently and was hesitating to buy it for the very reasons you mentionned.

capture one pro has offered color uniformity control since version 7? or 6? it's not new to version 20.

to be clear, the uniformity tool is distinct from the advanced color editing tool. you don't use it to select a hue-sat-lum range and then shift it (although you can if you want); rather, you use the uniformity tool to select a hue-sat-lum range and alter the degree of hue-sat-lum variation within that range. which is the exact thing you are complaining about and wish to correct in your images--the degree of hue variation in your skin tones.

but if you were "quite familiar" with it . . . well. huh. worth a try.

good luck!

 

[lélé777004]

. . . was made for you.

as jim and others have pointed out, raw conversion methodology and practice matters, here--possibly more than any other factor, including sensor cfa design.

if you are so serious--and particular--about your color that you are measuring and designing your own sensor profiles, that you are measuring white balance for black-body-radiation "accuracy" rather than for personal preference, then clearly it's time to become at least that much involved, conversant, skilled in your raw conversion methodology.

if you're concerned about hue variation over skin tones (or any color region) in your raw conversion, capture one is the converter you need to be using. because it offers the ability to edit hue, saturation, and luminance uniformity for any hue-saturation-luminance region you select. and it's not a major edit. it's easy, it's fast. you drop your mouse on the skin tone you want, you push the hue variation slider to lessen that hue region's degree of "drift" toward red or green over any breadth of saturation and luminance you'd like.

take a look.

Hello!

Thanks for your feedback.

I certainly do not pretend to have any particular skill with Capture One Pro, but I used to use it and I'm quite familiar with their colors tool. I can only agree: it's excellent!

I gave a try to version 20 of Capture One Pro recently and was hesitating to buy it for the very reasons you mentionned.

capture one pro has offered color uniformity control since version 7? or 6? it's not new to version 20.

Did I say that?!

I said I gave a try to version 20.
Purpose was to assess if I could see myself using it as my main RAW converter, instead of DxO Photo Lab. Answer is: no.
And one of the main reasons why I went into the hassle of trying again a software I let several years ago was their color tools...

to be clear, the uniformity tool is distinct from the advanced color editing tool. you don't use it to select a hue-sat-lum range and then shift it (although you can if you want); rather, you use the uniformity tool to select a hue-sat-lum range and alter the degree of hue-sat-lum variation within that range. which is the exact thing you are complaining about and wish to correct in your images--the degree of hue variation in your skin tones.

but if you were "quite familiar" with it . . . well. huh. worth a try.

I am.

But that's not really what I'm looking for...or maybe I'm not using it right?
Because not only it reduces the skin variations that I find unpleasant/unatural, but also other that are necessary to keep things natural.
Picking the colors that have the unpleasant 'shift' an applying a slight hue and saturation adjustment looks better to me.

That's for simple cases, for mixed light and that kind of stuf, that's a bit more complicated and I did not found any 'generic' workaround...

good luck!

 

[lélé777004]

Of course, the chart may no reflect actual skins reflective spectra. There might be some errors in some patches (I don't have a spectrophotometer to check). There might be some operator error (it's a difficult target to shoot due to glare and I struggled at the beginning). But what Lumariver tells from the target shot is in line with what I noticed before I started making profiles...

Does this help you understand what skin spectra look like?



Three skin readings, face, palm of hand, back of hand, for two people, and two different CC24 cards.

Jim

Hello Jim!

Thanks for sharing. Always interesting to lear from you.

To the layman I'm, the CC24 seems pretty close to the real thing. I'm pleasantly surprised.

In the real world, skin looks like a much more complex thing than 'just a matte surface'. With multiple layers, ligth penetrating inside... So I guess the reflected and scattered spectrum migth vary depending on the light position and the obersver position, isn't it?

 

[Erik Kaffehr]

Of course, the chart may no reflect actual skins reflective spectra. There might be some errors in some patches (I don't have a spectrophotometer to check). There might be some operator error (it's a difficult target to shoot due to glare and I struggled at the beginning). But what Lumariver tells from the target shot is in line with what I noticed before I started making profiles...

Does this help you understand what skin spectra look like?



Three skin readings, face, palm of hand, back of hand, for two people, and two different CC24 cards.

Jim

Hello Jim!

Thanks for sharing. Always interesting to lear from you.

To the layman I'm, the CC24 seems pretty close to the real thing. I'm pleasantly surprised.

In the real world, skin looks like a much more complex thing than 'just a matte surface'. With multiple layers, ligth penetrating inside... So I guess the reflected and scattered spectrum migth vary depending on the light position and the obersver position, isn't it?

Hi,

Skin is probably a lot about texture. It is sometimes worth separating color from luminance.

Best regards

Erik

--
Erik Kaffehr
Website: http://echophoto.dnsalias.net
Magic uses to disappear in controlled experiments…
Gallery: http://echophoto.smugmug.com
Articles: http://echophoto.dnsalias.net/ekr/index.php/photoarticles

 

[Erik Kaffehr]

I had a look at the portrait posted.

First i took two patches laid over each other with light and shadow Lab values, second I did the same but using the same L value. Here is a screen dump:







View attachment 588ec098bd0b40f7853cc0a4400152bc.jpg
Here is the JPEG. :-( Note how much the screen dump distorts the colors :-(

Looking at the Hsv coordinates the hue change would be on the red/yellow segment.

Just to say, it is a nice portrait and I like the colors.

Best regards
Erik

--
Erik Kaffehr
Website: http://echophoto.dnsalias.net
Magic uses to disappear in controlled experiments…
Gallery: http://echophoto.smugmug.com
Articles: http://echophoto.dnsalias.net/ekr/index.php/photoarticles

 

[lélé777004]

What I dislike the most in this illustration and looks like what I get in many, many, of my shots is the color variations in the area around her mouth. Especially the small area below her inferior lips.

Now I see it. I agree that it looks greenish, not necessarily because it is; probably because it is surrounded by pink and red - but it does look unnatural.

Yeah, might be the reason why it looks 'too green' to me!

If so, that's the simultaneous contrast issue that Iliah mentioned earlier.

Yes, got it.

By the way, there are imperfect standard observers for constant-color fields, but, AFAIK, there are no standard models for simultaneous contrast color effects, and it is certainly possible (and I think, likely) that the quantitative effects are different in different people. This would not be detected by any color normalcy testing that I know of.

Jim

I know that I'm very sensitive to color contrast. Let's say a car which was partially repainted, I might spot it. (Even if I have to admit that sometimes it is really, really, well done and invisible.)
But I always thought it was more a question of temperament, demanding nature and attention do details...

In the case of the 'hue shift' accross faces, this makes me feel uncomfortable. Like if I was looking at sick people. Really unpleasant (but highly subjective and maybe cultural).

It's quite amazing, because for example when I did my first CCSG shots, results were sh** due to glare. This gave me oversaturated skin tones...but after hours looking at the same images, I could not see it anymore.
On the other hand, a slight variation accross the face: I feel uncomfortable. I also try the other way around, using Capture One Pro Color Palet or DxO Photo Lab HSL tool to 'uniformize' hue a bit: it's even worse.

All that said another problem I have is how the color rendering of skin tones seems to variy with different lighting. I have an old stock of Canon 300D (mly first DSLR), Canon 350D and Canon EOS 40D photos of the same persons photographed with different lighting, including catastrophic mixed lighting (for example natural light + integrated flash for fill-in) and skin tones much more consistent from shot to shot. It's with Canon in-camera processing through or it's DxO Photo Lab/Lightroom/Capture One Pro sibbling. So it remain to be seen what it would look like withotu all these subjective adjustments Canon do...
I'll try to find or make a more 'neutral' profile and see...

I would recall that I have seen an article by TheSuede on the Fred Miranda forums about CFA designs.
What he sort of said that Canon has taken a route that works well for mixed light while some other sensors were optimized for like shooting in the studio.
I would recall that both TheSuede and Iliah Borg pretty much considered the CFA design on the Sony A900 to be a pretty decent compromise regarding color rendition and SNR.
I had some discussions regarding the color rendition of the Phase One P45+ back I have with Tim Parkin. Tim Parkin and his friend Joe Cornish had issues with yellow contamination of chlorophyll greens. I have seen that, too, but I hoped that DCP profiles would be able to handle that.
In the end, we have found out that Tim and I had different interpretations of color, although I must say that I would lean to Tim being right.
One of the things I considered was that the IR filter (or hot mirror) design may have played a role.
Interestingly, a couple of years ago, Phase One introduced a new back, called 'Thricomatic'. They produced some explanations that ignored pretty much all color science ever developed. But, reading between the lines it may be concluded that there were modifications to the 'hot filter'. What I have seen from real worlds samples, the new Thrichromatic back did not have that yellow contamination of vegetable greens I have seen on my P45+ back and on the IQ 3100 MP I have seen tested.

Lime green seems to have extreme characteristics in the near IR (infra red) region. That was one of the reasons I include lime green in my 'tricolore' tests. But I found that all the three sensorsi tried (Phase One P45+, Sony Alpha 900 and Sony A7rII) did a decent job on that lime.
In the end, I don't pretend to know...

Thanks for sharing.

I read a few posts from theSuede on Fred Miranda's forum, as well as a few articles on the web.

My 'layman takeaways' + some questions:

• Two different light spectra can appear as the same color to an observer (human, camera...) (I did know). In such a case, these two different spectra are called 'metamers' (I did not know) and the perceived matching 'metamerism' (I did know).
• If the perceived color matching of two patches falls apart under a different illuminant, it's called 'illuminant metameric failure' (I did know this can happen - and learnt it the hard way! - but I did not know how it was called).
• One observer may see the same color, but not another observer. It's called 'observer metameric failure'. (I did know that because of my father who is colorblind: sometimes he sees two different colors while I see the same, sometimes the opposite. But neither I thought about implications for cameras, nor I knew how ti was called.)
  Then I fall into the complete unknown...!
• theSuede talks about 'hue resolution' and 'metameric failure' (I guess he means: 'observer metameric failure').
  My layman understanding is that the two are closely linked to the sensor 'spectral response' (linked itself to CFA design, silicium and other stuff I don't know...). Correct?
  Also, that the 'hue resolution' and 'metameric failure' maybe somewhat related: sometimes the sensor may be unable to distinguish two different spectra because of an 'insufficient' hue resolution. Really not sure about this one, is it correct?
  And if it fails while a human observer would be able to pick the difference, that's a 'metameric failure' and may cause problem. Correct?
  What leads me to another question: what happens when the camera can pick a difference and not the human observer?.
• theSuede also says (if I understand correctly) speaking about the Canon 5D Mark II (with apparently new CFA design) that the 'hue resolution' in the orange-green would be low, what would lead to minimize color variations in skin tones. (He does not mention that, but I guess this is in addition to the subjective adjustment Canon makes in its color profiles). May this be correct?
  May it explain (in addition to the subjective adjustments made in their color profiles) why some Canon bodies give 'more consistent' skin tones?
  ('More consistent' in the sense there are less color variations depending on the lighting and people complexion.)

Thanks!

 

[lélé777004]

I had a look at the portrait posted.

First i took two patches laid over each other with light and shadow Lab values, second I did the same but using the same L value. Here is a screen dump:



View attachment 588ec098bd0b40f7853cc0a4400152bc.jpg
Here is the JPEG. :-( Note how much the screen dump distorts the colors :-(

Looking at the Hsv coordinates the hue change would be on the red/yellow segment.

Just to say, it is a nice portrait and I like the colors.

Best regards
Erik

Thanks for looking closely.

That's what Jim said (shift toward yellow).

That's what I see with the patches superimposed.
Thats' not what I see in the actual picture, at least in some areas (in paricular below the lips). It looks like the brown has 'a greenish cast'.
Some say it maybe a color contrast effects.

 

[Erik Kaffehr]

What I dislike the most in this illustration and looks like what I get in many, many, of my shots is the color variations in the area around her mouth. Especially the small area below her inferior lips.

Now I see it. I agree that it looks greenish, not necessarily because it is; probably because it is surrounded by pink and red - but it does look unnatural.

Yeah, might be the reason why it looks 'too green' to me!

If so, that's the simultaneous contrast issue that Iliah mentioned earlier.

Yes, got it.

By the way, there are imperfect standard observers for constant-color fields, but, AFAIK, there are no standard models for simultaneous contrast color effects, and it is certainly possible (and I think, likely) that the quantitative effects are different in different people. This would not be detected by any color normalcy testing that I know of.

Jim

I know that I'm very sensitive to color contrast. Let's say a car which was partially repainted, I might spot it. (Even if I have to admit that sometimes it is really, really, well done and invisible.)
But I always thought it was more a question of temperament, demanding nature and attention do details...

In the case of the 'hue shift' accross faces, this makes me feel uncomfortable. Like if I was looking at sick people. Really unpleasant (but highly subjective and maybe cultural).

It's quite amazing, because for example when I did my first CCSG shots, results were sh** due to glare. This gave me oversaturated skin tones...but after hours looking at the same images, I could not see it anymore.
On the other hand, a slight variation accross the face: I feel uncomfortable. I also try the other way around, using Capture One Pro Color Palet or DxO Photo Lab HSL tool to 'uniformize' hue a bit: it's even worse.

All that said another problem I have is how the color rendering of skin tones seems to variy with different lighting. I have an old stock of Canon 300D (mly first DSLR), Canon 350D and Canon EOS 40D photos of the same persons photographed with different lighting, including catastrophic mixed lighting (for example natural light + integrated flash for fill-in) and skin tones much more consistent from shot to shot. It's with Canon in-camera processing through or it's DxO Photo Lab/Lightroom/Capture One Pro sibbling. So it remain to be seen what it would look like withotu all these subjective adjustments Canon do...
I'll try to find or make a more 'neutral' profile and see...

I would recall that I have seen an article by TheSuede on the Fred Miranda forums about CFA designs.
What he sort of said that Canon has taken a route that works well for mixed light while some other sensors were optimized for like shooting in the studio.
I would recall that both TheSuede and Iliah Borg pretty much considered the CFA design on the Sony A900 to be a pretty decent compromise regarding color rendition and SNR.
I had some discussions regarding the color rendition of the Phase One P45+ back I have with Tim Parkin. Tim Parkin and his friend Joe Cornish had issues with yellow contamination of chlorophyll greens. I have seen that, too, but I hoped that DCP profiles would be able to handle that.
In the end, we have found out that Tim and I had different interpretations of color, although I must say that I would lean to Tim being right.
One of the things I considered was that the IR filter (or hot mirror) design may have played a role.
Interestingly, a couple of years ago, Phase One introduced a new back, called 'Thricomatic'. They produced some explanations that ignored pretty much all color science ever developed. But, reading between the lines it may be concluded that there were modifications to the 'hot filter'. What I have seen from real worlds samples, the new Thrichromatic back did not have that yellow contamination of vegetable greens I have seen on my P45+ back and on the IQ 3100 MP I have seen tested.

Lime green seems to have extreme characteristics in the near IR (infra red) region. That was one of the reasons I include lime green in my 'tricolore' tests. But I found that all the three sensorsi tried (Phase One P45+, Sony Alpha 900 and Sony A7rII) did a decent job on that lime.
In the end, I don't pretend to know...

Thanks for sharing.

I read a few posts from theSuede on Fred Miranda's forum, as well as a few articles on the web.

My 'layman takeaways' + some questions:

• Two different light spectra can appear as the same color to an observer (human, camera...) (I did know). In such a case, these two different spectra are called 'metamers' (I did not know) and the perceived matching 'metamerism' (I did know).
• If the perceived color matching of two patches falls apart under a different illuminant, it's called 'illuminant metameric failure' (I did know this can happen - and learnt it the hard way! - but I did not know how it was called).
• One observer may see the same color, but not another observer. It's called 'observer metameric failure'. (I did know that because of my father who is colorblind: sometimes he sees two different colors while I see the same, sometimes the opposite. But I never thought about implication for cameras.)
  Then I fall into the complete unknown...
• theSuede talks about 'hue resolution' and 'metameric failure' (I guess he means: 'observer metameric failure').
  My layman understanding is that the two are closely linked to the sensor 'spectral response' (linked itself to CFA design, silicium and other stuff I don't know...). Correct?
  Also, that the 'hue resolution' and 'metameric failure' maybe somewhat related: sometimes the sensor may be unable to distinguish two different spectra because of an 'insufficient' hue resolution. Really not sure about this one, is it correct?
  And if it fails while a human observer would be able to pick the difference, that's a 'metameric failure' and may cause problem. Correct?
  What leads me to another question: what happens when the camera can pick a difference and not the human observer?.
• theSuede also says speaking about 5D Mark II (with apparently new CFA design) that the 'hue resolution' in the orange-green would be low, what would lead to minimize color differences in skin tones. (He does not mention that, but I guess this is in addition to the subjective adjustment Canon makes in its color profiles). May this be correct?
  May it explain (in addition to the subjective adjustments made in their color profiles) why some Canon bodies give 'more consistent' skin tones?
  ('More consistent' in the sense there are less color variations depending on the lighting and people complexion.)

Thanks!

Hi,

With regard to hue resolution, it may be conceivable that a sensor would be more or less sensitive to a change of wave length across the spectrum:

Source

In this case, the sensor would be pretty blind to differences in color between 640 and 750 microns, as it would only have one signal,

On the other hand, a change at 570 nm would have a huge effect.

If the camera detects a color difference invisible to a human observer, I would argue that would be an observer metameric failure, with the cameras as an observer.

A few years ago, Phase One introduced a new sensor with, what they stated, new CFA design. Their description was a bit questionable, which caused Jack Hogan and Jim Kasson to look into CFA and Luther-Ives.

Jack published a series of articles on the Thrichromatic: starting here .

The cooperation of Jack and Jim resulted in this nice article:

https://www.strollswithmydog.com/perfect-color-filter-array/



I think that Jack's article shows that good accuracy can achieved with a great variety of CFA designs.

In addition, the IR-filter characteristics also play a role.

Best regards

Erik

--
Erik Kaffehr
Website: http://echophoto.dnsalias.net
Magic uses to disappear in controlled experiments…
Gallery: http://echophoto.smugmug.com
Articles: http://echophoto.dnsalias.net/ekr/index.php/photoarticles

 

[lélé777004]

What I dislike the most in this illustration and looks like what I get in many, many, of my shots is the color variations in the area around her mouth. Especially the small area below her inferior lips.

Now I see it. I agree that it looks greenish, not necessarily because it is; probably because it is surrounded by pink and red - but it does look unnatural.

Yeah, might be the reason why it looks 'too green' to me!

If so, that's the simultaneous contrast issue that Iliah mentioned earlier.

Yes, got it.

By the way, there are imperfect standard observers for constant-color fields, but, AFAIK, there are no standard models for simultaneous contrast color effects, and it is certainly possible (and I think, likely) that the quantitative effects are different in different people. This would not be detected by any color normalcy testing that I know of.

Jim

I know that I'm very sensitive to color contrast. Let's say a car which was partially repainted, I might spot it. (Even if I have to admit that sometimes it is really, really, well done and invisible.)
But I always thought it was more a question of temperament, demanding nature and attention do details...

In the case of the 'hue shift' accross faces, this makes me feel uncomfortable. Like if I was looking at sick people. Really unpleasant (but highly subjective and maybe cultural).

It's quite amazing, because for example when I did my first CCSG shots, results were sh** due to glare. This gave me oversaturated skin tones...but after hours looking at the same images, I could not see it anymore.
On the other hand, a slight variation accross the face: I feel uncomfortable. I also try the other way around, using Capture One Pro Color Palet or DxO Photo Lab HSL tool to 'uniformize' hue a bit: it's even worse.

All that said another problem I have is how the color rendering of skin tones seems to variy with different lighting. I have an old stock of Canon 300D (mly first DSLR), Canon 350D and Canon EOS 40D photos of the same persons photographed with different lighting, including catastrophic mixed lighting (for example natural light + integrated flash for fill-in) and skin tones much more consistent from shot to shot. It's with Canon in-camera processing through or it's DxO Photo Lab/Lightroom/Capture One Pro sibbling. So it remain to be seen what it would look like withotu all these subjective adjustments Canon do...
I'll try to find or make a more 'neutral' profile and see...

I would recall that I have seen an article by TheSuede on the Fred Miranda forums about CFA designs.
What he sort of said that Canon has taken a route that works well for mixed light while some other sensors were optimized for like shooting in the studio.
I would recall that both TheSuede and Iliah Borg pretty much considered the CFA design on the Sony A900 to be a pretty decent compromise regarding color rendition and SNR.
I had some discussions regarding the color rendition of the Phase One P45+ back I have with Tim Parkin. Tim Parkin and his friend Joe Cornish had issues with yellow contamination of chlorophyll greens. I have seen that, too, but I hoped that DCP profiles would be able to handle that.
In the end, we have found out that Tim and I had different interpretations of color, although I must say that I would lean to Tim being right.
One of the things I considered was that the IR filter (or hot mirror) design may have played a role.
Interestingly, a couple of years ago, Phase One introduced a new back, called 'Thricomatic'. They produced some explanations that ignored pretty much all color science ever developed. But, reading between the lines it may be concluded that there were modifications to the 'hot filter'. What I have seen from real worlds samples, the new Thrichromatic back did not have that yellow contamination of vegetable greens I have seen on my P45+ back and on the IQ 3100 MP I have seen tested.

Lime green seems to have extreme characteristics in the near IR (infra red) region. That was one of the reasons I include lime green in my 'tricolore' tests. But I found that all the three sensorsi tried (Phase One P45+, Sony Alpha 900 and Sony A7rII) did a decent job on that lime.
In the end, I don't pretend to know...

Thanks for sharing.

I read a few posts from theSuede on Fred Miranda's forum, as well as a few articles on the web.

My 'layman takeaways' + some questions:

• Two different light spectra can appear as the same color to an observer (human, camera...) (I did know). In such a case, these two different spectra are called 'metamers' (I did not know) and the perceived matching 'metamerism' (I did know).
• If the perceived color matching of two patches falls apart under a different illuminant, it's called 'illuminant metameric failure' (I did know this can happen - and learnt it the hard way! - but I did not know how it was called).
• One observer may see the same color, but not another observer. It's called 'observer metameric failure'. (I did know that because of my father who is colorblind: sometimes he sees two different colors while I see the same, sometimes the opposite. But I never thought about implication for cameras.)
  Then I fall into the complete unknown...
• theSuede talks about 'hue resolution' and 'metameric failure' (I guess he means: 'observer metameric failure').
  My layman understanding is that the two are closely linked to the sensor 'spectral response' (linked itself to CFA design, silicium and other stuff I don't know...). Correct?
  Also, that the 'hue resolution' and 'metameric failure' maybe somewhat related: sometimes the sensor may be unable to distinguish two different spectra because of an 'insufficient' hue resolution. Really not sure about this one, is it correct?
  And if it fails while a human observer would be able to pick the difference, that's a 'metameric failure' and may cause problem. Correct?
  What leads me to another question: what happens when the camera can pick a difference and not the human observer?.
• theSuede also says speaking about 5D Mark II (with apparently new CFA design) that the 'hue resolution' in the orange-green would be low, what would lead to minimize color differences in skin tones. (He does not mention that, but I guess this is in addition to the subjective adjustment Canon makes in its color profiles). May this be correct?
  May it explain (in addition to the subjective adjustments made in their color profiles) why some Canon bodies give 'more consistent' skin tones?
  ('More consistent' in the sense there are less color variations depending on the lighting and people complexion.)

Thanks!

Hi,

With regard to hue resolution, it may be conceivable that a sensor would be more or less sensitive to a change of wave length across the spectrum:

Source

In this case, the sensor would be pretty blind to differences in color between 640 and 750 microns, as it would only have one signal,

On the other hand, a change at 570 nm would have a huge effect.

If the camera detects a color difference invisible to a human observer, I would argue that would be an observer metameric failure, with the cameras as an observer.

A few years ago, Phase One introduced a new sensor with, what they stated, new CFA design. Their description was a bit questionable, which caused Jack Hogan and Jim Kasson to look into CFA and Luther-Ives.

Jack published a series of articles on the Thrichromatic: starting here .

The cooperation of Jack and Jim resulted in this nice article:

https://www.strollswithmydog.com/perfect-color-filter-array/

I think that Jack's article shows that good accuracy can achieved with a great variety of CFA designs.

In addition, the IR-filter characteristics also play a role.

Best regards

Erik

Many thanks for your insight and the links.

I found that about the Canon EOS 5D Mark II:

source: http://www.astrosurf.com/buil/50d/test.htm

If I get it correctly, hue resolution would be quite 'low' between ~530 and 550nm, right ?

 

[D Cox]

What I dislike the most in this illustration and looks like what I get in many, many, of my shots is the color variations in the area around her mouth. Especially the small area below her inferior lips.

Now I see it. I agree that it looks greenish, not necessarily because it is; probably because it is surrounded by pink and red - but it does look unnatural.

Variation of makeup in different parts of the face ?

I don't find any colour photos of people to have convincing skin colours. For good skin colours, use oil or acrylic paint, built up in layers, with white and iron oxide pigments. See originals (not printed reproductions) by Rembrandt, Velasquez, Goya or many lesser artists of the same period.

Photographs of people are better in monochrome.

In the case of fashion shots, what is wanted is good makeup colours, rather than skin colours.

 

[D Cox]

What I dislike the most in this illustration and looks like what I get in many, many, of my shots is the color variations in the area around her mouth. Especially the small area below her inferior lips.

Now I see it. I agree that it looks greenish, not necessarily because it is; probably because it is surrounded by pink and red - but it does look unnatural.

Yeah, might be the reason why it looks 'too green' to me!

If so, that's the simultaneous contrast issue that Iliah mentioned earlier.

Simultaneous contrast could vary with monitor brightness, light adaptation, and individual variations in vision.

 

[D Cox]

What I dislike the most in this illustration and looks like what I get in many, many, of my shots is the color variations in the area around her mouth. Especially the small area below her inferior lips.

Now I see it. I agree that it looks greenish, not necessarily because it is; probably because it is surrounded by pink and red - but it does look unnatural.

Yeah, might be the reason why it looks 'too green' to me!

If so, that's the simultaneous contrast issue that Iliah mentioned earlier.

Yes, got it.

By the way, there are imperfect standard observers for constant-color fields, but, AFAIK, there are no standard models for simultaneous contrast color effects, and it is certainly possible (and I think, likely) that the quantitative effects are different in different people. This would not be detected by any color normalcy testing that I know of.

Jim

I know that I'm very sensitive to color contrast. Let's say a car which was partially repainted, I might spot it. (Even if I have to admit that sometimes it is really, really, well done and invisible.)
But I always thought it was more a question of temperament, demanding nature and attention do details...

In the case of the 'hue shift' accross faces, this makes me feel uncomfortable. Like if I was looking at sick people. Really unpleasant (but highly subjective and maybe cultural).

It's quite amazing, because for example when I did my first CCSG shots, results were sh** due to glare. This gave me oversaturated skin tones...but after hours looking at the same images, I could not see it anymore.
On the other hand, a slight variation accross the face: I feel uncomfortable. I also try the other way around, using Capture One Pro Color Palet or DxO Photo Lab HSL tool to 'uniformize' hue a bit: it's even worse.

All that said another problem I have is how the color rendering of skin tones seems to variy with different lighting. I have an old stock of Canon 300D (mly first DSLR), Canon 350D and Canon EOS 40D photos of the same persons photographed with different lighting, including catastrophic mixed lighting (for example natural light + integrated flash for fill-in) and skin tones much more consistent from shot to shot. It's with Canon in-camera processing through or it's DxO Photo Lab/Lightroom/Capture One Pro sibbling. So it remain to be seen what it would look like withotu all these subjective adjustments Canon do...
I'll try to find or make a more 'neutral' profile and see...

I would recall that I have seen an article by TheSuede on the Fred Miranda forums about CFA designs.
What he sort of said that Canon has taken a route that works well for mixed light while some other sensors were optimized for like shooting in the studio.
I would recall that both TheSuede and Iliah Borg pretty much considered the CFA design on the Sony A900 to be a pretty decent compromise regarding color rendition and SNR.
I had some discussions regarding the color rendition of the Phase One P45+ back I have with Tim Parkin. Tim Parkin and his friend Joe Cornish had issues with yellow contamination of chlorophyll greens. I have seen that, too, but I hoped that DCP profiles would be able to handle that.
In the end, we have found out that Tim and I had different interpretations of color, although I must say that I would lean to Tim being right.
One of the things I considered was that the IR filter (or hot mirror) design may have played a role.
Interestingly, a couple of years ago, Phase One introduced a new back, called 'Thricomatic'. They produced some explanations that ignored pretty much all color science ever developed. But, reading between the lines it may be concluded that there were modifications to the 'hot filter'. What I have seen from real worlds samples, the new Thrichromatic back did not have that yellow contamination of vegetable greens I have seen on my P45+ back and on the IQ 3100 MP I have seen tested.

Lime green seems to have extreme characteristics in the near IR (infra red) region. That was one of the reasons I include lime green in my 'tricolore' tests. But I found that all the three sensorsi tried (Phase One P45+, Sony Alpha 900 and Sony A7rII) did a decent job on that lime.
In the end, I don't pretend to know...

Are you talking about greens on real leaves, or greens on paint samples or test cards ? The latter are not likely to reflect as much IR as leaves and flowers do.

 

[J A C S]

Of course, the chart may no reflect actual skins reflective spectra. There might be some errors in some patches (I don't have a spectrophotometer to check). There might be some operator error (it's a difficult target to shoot due to glare and I struggled at the beginning). But what Lumariver tells from the target shot is in line with what I noticed before I started making profiles...

Does this help you understand what skin spectra look like?



Three skin readings, face, palm of hand, back of hand, for two people, and two different CC24 cards.

Jim

Hello Jim!

Thanks for sharing. Always interesting to lear from you.

To the layman I'm, the CC24 seems pretty close to the real thing. I'm pleasantly surprised.

I would not be so quick to declare that. First, there is a noticeable dip in the green area, where our eyes have the highest sensitivity. Second, we are looking at curves and trying to extrapolate from here how close those reflectivities would look to us under various lighting conditions; and those are different things.

 

[J A C S]

What I dislike the most in this illustration and looks like what I get in many, many, of my shots is the color variations in the area around her mouth. Especially the small area below her inferior lips.

Now I see it. I agree that it looks greenish, not necessarily because it is; probably because it is surrounded by pink and red - but it does look unnatural.

Variation of makeup in different parts of the face ?

Definitely not.

 

[lélé777004]

What I dislike the most in this illustration and looks like what I get in many, many, of my shots is the color variations in the area around her mouth. Especially the small area below her inferior lips.

Now I see it. I agree that it looks greenish, not necessarily because it is; probably because it is surrounded by pink and red - but it does look unnatural.

Variation of makeup in different parts of the face ?

Definitely not.

In any case: I used this DPRview sample as an illustration.

But I have the same with my 6 and 7-year children.
They don't wear makeup!

 

[JimKasson]

What leads me to another question: what happens when the camera can pick a difference and not the human observer?.

That case is covered here:

https://blog.kasson.com/the-last-word/metameric-failure/

Jim

--
https://blog.kasson.com

 

[J A C S]

What I dislike the most in this illustration and looks like what I get in many, many, of my shots is the color variations in the area around her mouth. Especially the small area below her inferior lips.

Now I see it. I agree that it looks greenish, not necessarily because it is; probably because it is surrounded by pink and red - but it does look unnatural.

Yeah, might be the reason why it looks 'too green' to me!

If so, that's the simultaneous contrast issue that Iliah mentioned earlier.

Yes, got it.

By the way, there are imperfect standard observers for constant-color fields, but, AFAIK, there are no standard models for simultaneous contrast color effects, and it is certainly possible (and I think, likely) that the quantitative effects are different in different people. This would not be detected by any color normalcy testing that I know of.

Jim

I know that I'm very sensitive to color contrast. Let's say a car which was partially repainted, I might spot it. (Even if I have to admit that sometimes it is really, really, well done and invisible.)
But I always thought it was more a question of temperament, demanding nature and attention do details...

In the case of the 'hue shift' accross faces, this makes me feel uncomfortable. Like if I was looking at sick people. Really unpleasant (but highly subjective and maybe cultural).

It's quite amazing, because for example when I did my first CCSG shots, results were sh** due to glare. This gave me oversaturated skin tones...but after hours looking at the same images, I could not see it anymore.
On the other hand, a slight variation accross the face: I feel uncomfortable. I also try the other way around, using Capture One Pro Color Palet or DxO Photo Lab HSL tool to 'uniformize' hue a bit: it's even worse.

All that said another problem I have is how the color rendering of skin tones seems to variy with different lighting. I have an old stock of Canon 300D (mly first DSLR), Canon 350D and Canon EOS 40D photos of the same persons photographed with different lighting, including catastrophic mixed lighting (for example natural light + integrated flash for fill-in) and skin tones much more consistent from shot to shot. It's with Canon in-camera processing through or it's DxO Photo Lab/Lightroom/Capture One Pro sibbling. So it remain to be seen what it would look like withotu all these subjective adjustments Canon do...
I'll try to find or make a more 'neutral' profile and see...

I would recall that I have seen an article by TheSuede on the Fred Miranda forums about CFA designs.
What he sort of said that Canon has taken a route that works well for mixed light while some other sensors were optimized for like shooting in the studio.
I would recall that both TheSuede and Iliah Borg pretty much considered the CFA design on the Sony A900 to be a pretty decent compromise regarding color rendition and SNR.
I had some discussions regarding the color rendition of the Phase One P45+ back I have with Tim Parkin. Tim Parkin and his friend Joe Cornish had issues with yellow contamination of chlorophyll greens. I have seen that, too, but I hoped that DCP profiles would be able to handle that.
In the end, we have found out that Tim and I had different interpretations of color, although I must say that I would lean to Tim being right.
One of the things I considered was that the IR filter (or hot mirror) design may have played a role.
Interestingly, a couple of years ago, Phase One introduced a new back, called 'Thricomatic'. They produced some explanations that ignored pretty much all color science ever developed. But, reading between the lines it may be concluded that there were modifications to the 'hot filter'. What I have seen from real worlds samples, the new Thrichromatic back did not have that yellow contamination of vegetable greens I have seen on my P45+ back and on the IQ 3100 MP I have seen tested.

Lime green seems to have extreme characteristics in the near IR (infra red) region. That was one of the reasons I include lime green in my 'tricolore' tests. But I found that all the three sensorsi tried (Phase One P45+, Sony Alpha 900 and Sony A7rII) did a decent job on that lime.
In the end, I don't pretend to know...

Thanks for sharing.

I read a few posts from theSuede on Fred Miranda's forum, as well as a few articles on the web.

My 'layman takeaways' + some questions:

• Two different light spectra can appear as the same color to an observer (human, camera...) (I did know). In such a case, these two different spectra are called 'metamers' (I did not know) and the perceived matching 'metamerism' (I did know).
• If the perceived color matching of two patches falls apart under a different illuminant, it's called 'illuminant metameric failure' (I did know this can happen - and learnt it the hard way! - but I did not know how it was called).
• One observer may see the same color, but not another observer. It's called 'observer metameric failure'. (I did know that because of my father who is colorblind: sometimes he sees two different colors while I see the same, sometimes the opposite. But I never thought about implication for cameras.)
  Then I fall into the complete unknown...
• theSuede talks about 'hue resolution' and 'metameric failure' (I guess he means: 'observer metameric failure').
  My layman understanding is that the two are closely linked to the sensor 'spectral response' (linked itself to CFA design, silicium and other stuff I don't know...). Correct?
  Also, that the 'hue resolution' and 'metameric failure' maybe somewhat related: sometimes the sensor may be unable to distinguish two different spectra because of an 'insufficient' hue resolution. Really not sure about this one, is it correct?
  And if it fails while a human observer would be able to pick the difference, that's a 'metameric failure' and may cause problem. Correct?
  What leads me to another question: what happens when the camera can pick a difference and not the human observer?.

Most of this is basic linear algebra. You have a linear operator (projection) which maps the real world to the captured colors (yes, I will all them colors) and your eyes do the same but with a somewhat different operator. Think of it as projections under different angles. Sometimes two different spectral densities would be projected (viewed) the same by the sensor but not by you. Those are colors you can distinguish but the sensor cannot. On the other hand, this means that there must be spectra which the sensor will distinguish but you cannot. What happens then depends on how the signal is processed - if by a color matrix only, this means the photo will show real color variations in some cases when you cannot see any.

A slightly more complicated version of that is to put a threshold/sensitivity of what differences you can see or the sensor can distinguish and then you can see, etc.

• theSuede also says speaking about 5D Mark II (with apparently new CFA design) that the 'hue resolution' in the orange-green would be low, what would lead to minimize color differences in skin tones. (He does not mention that, but I guess this is in addition to the subjective adjustment Canon makes in its color profiles). May this be correct?
  May it explain (in addition to the subjective adjustments made in their color profiles) why some Canon bodies give 'more consistent' skin tones?
  ('More consistent' in the sense there are less color variations depending on the lighting and people complexion.)

Thanks!

The post I have seen here is highly speculative and I would ignore it, see also below.

Hi,

With regard to hue resolution, it may be conceivable that a sensor would be more or less sensitive to a change of wave length across the spectrum:

Source

In this case, the sensor would be pretty blind to differences in color between 640 and 750 microns, as it would only have one signal,

So does your eye. Such an analysis must be done in a comparison to the human vision. The problem I see above is that the red curve is too narrow and misses a lot of the 500-550 band or so; and this it does not seem to be possible to compensate for it by the color matrix.

On the other hand, a change at 570 nm would have a huge effect.

Your eyes react similarly.

Many thanks for your insight and the links.

I found that about the Canon EOS 5D Mark II:

source: http://www.astrosurf.com/buil/50d/test.htm

If I get it correctly, hue resolution would be quite 'low' between ~530 and 550nm, right ?

It is hard to answer questions like this before we compute a "good" color matrix. The small red bump would be compensated to some extent by the green one. We have to see what is left and then understand how sensitive to the error left we are, etc. Something like this was done in the threads mentioned above.

 

[Iliah Borg]

Source

In this case, the sensor would be pretty blind to differences in color between 640 and 750 microns

From my measurements of D700, spectral responses in blue and green channels are non-zero in that range, and it is typical for a sensor with an IR filter to have 700 nm at cut-off.
--

About LibRaw | LibRaw

www.libraw.org

 

[Erik Kaffehr]

What I dislike the most in this illustration and looks like what I get in many, many, of my shots is the color variations in the area around her mouth. Especially the small area below her inferior lips.

Now I see it. I agree that it looks greenish, not necessarily because it is; probably because it is surrounded by pink and red - but it does look unnatural.

Yeah, might be the reason why it looks 'too green' to me!

If so, that's the simultaneous contrast issue that Iliah mentioned earlier.

Yes, got it.

By the way, there are imperfect standard observers for constant-color fields, but, AFAIK, there are no standard models for simultaneous contrast color effects, and it is certainly possible (and I think, likely) that the quantitative effects are different in different people. This would not be detected by any color normalcy testing that I know of.

Jim

I know that I'm very sensitive to color contrast. Let's say a car which was partially repainted, I might spot it. (Even if I have to admit that sometimes it is really, really, well done and invisible.)
But I always thought it was more a question of temperament, demanding nature and attention do details...

In the case of the 'hue shift' accross faces, this makes me feel uncomfortable. Like if I was looking at sick people. Really unpleasant (but highly subjective and maybe cultural).

It's quite amazing, because for example when I did my first CCSG shots, results were sh** due to glare. This gave me oversaturated skin tones...but after hours looking at the same images, I could not see it anymore.
On the other hand, a slight variation accross the face: I feel uncomfortable. I also try the other way around, using Capture One Pro Color Palet or DxO Photo Lab HSL tool to 'uniformize' hue a bit: it's even worse.

All that said another problem I have is how the color rendering of skin tones seems to variy with different lighting. I have an old stock of Canon 300D (mly first DSLR), Canon 350D and Canon EOS 40D photos of the same persons photographed with different lighting, including catastrophic mixed lighting (for example natural light + integrated flash for fill-in) and skin tones much more consistent from shot to shot. It's with Canon in-camera processing through or it's DxO Photo Lab/Lightroom/Capture One Pro sibbling. So it remain to be seen what it would look like withotu all these subjective adjustments Canon do...
I'll try to find or make a more 'neutral' profile and see...

I would recall that I have seen an article by TheSuede on the Fred Miranda forums about CFA designs.
What he sort of said that Canon has taken a route that works well for mixed light while some other sensors were optimized for like shooting in the studio.
I would recall that both TheSuede and Iliah Borg pretty much considered the CFA design on the Sony A900 to be a pretty decent compromise regarding color rendition and SNR.
I had some discussions regarding the color rendition of the Phase One P45+ back I have with Tim Parkin. Tim Parkin and his friend Joe Cornish had issues with yellow contamination of chlorophyll greens. I have seen that, too, but I hoped that DCP profiles would be able to handle that.
In the end, we have found out that Tim and I had different interpretations of color, although I must say that I would lean to Tim being right.
One of the things I considered was that the IR filter (or hot mirror) design may have played a role.
Interestingly, a couple of years ago, Phase One introduced a new back, called 'Thricomatic'. They produced some explanations that ignored pretty much all color science ever developed. But, reading between the lines it may be concluded that there were modifications to the 'hot filter'. What I have seen from real worlds samples, the new Thrichromatic back did not have that yellow contamination of vegetable greens I have seen on my P45+ back and on the IQ 3100 MP I have seen tested.

Lime green seems to have extreme characteristics in the near IR (infra red) region. That was one of the reasons I include lime green in my 'tricolore' tests. But I found that all the three sensorsi tried (Phase One P45+, Sony Alpha 900 and Sony A7rII) did a decent job on that lime.
In the end, I don't pretend to know...

Are you talking about greens on real leaves, or greens on paint samples or test cards ? The latter are not likely to reflect as much IR as leaves and flowers do.

Hi,

Things like grass, leaves and lime fruits.

Lime fruits were suggested as a demonstration of the difference between Phase One's traditional IQ3100 MP back and their IQ 3100 MP Trichromatic.

The lime fruits I have tested with my P45+ were just fine in my test.

Best regards

Erik

 

[Erik Kaffehr]

Source

In this case, the sensor would be pretty blind to differences in color between 640 and 750 microns

From my measurements of D700, spectral responses in blue and green channels are non-zero in that range, and it is typical for a sensor with an IR filter to have 700 nm at cut-off.

Thanks for the comments! I didn't want to be negative about about the D700 just illustrate some details

--
Erik Kaffehr
Website: http://echophoto.dnsalias.net
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