Attention: Fotogenic & Custom Curve Users

[Bill Janes]

I had originally entered into these discussions with the belief that my D70 consistently underexposed images, but after reading the postings by Fotogenic and others, I have come to the realization that the D70's exposure is accurate, but that one must choose the proper tone curve that one applies either in the camera in the jpeg mode or in the NEF converter with raw files to get properly exposed highlights. The purpose of this post is to compare Fotogenic's PS4 curve to the results of 0.5 stop positive exposure compensation with Nikons Normal tone compensation (which he advised me to do in earlier posting for a proper comparison) and to describe an easy and quantitative method of doing so. I don't expect many responses to this post, but it may interest a few.

Fotogenics analysis this matter is the best that I have seen on the subject, and you should read it if you have not already done so:

http://fotogenetic.dearingfilm.com/custom_tone_curves.html

As he describes, you can photograph a gray card at various exposures, bracketing around the exposure indcated by the light meter for a particular ISO, and plot the pixel value in the resulting picture to obtain the characteristic curve for those conditions. This is the method used by Ansel Adams in his book The Negative. The exposure that reproduces the pixel level of the gray card is the proper one.

Actually, when using a gray card determine exosure, one should increase the indicated exposure by 1/2 f/stop (0.5 EV). See Thom Hogan's essay:

http://www.bythom.com/graycards.htm

What is the pixel level that one should get from taking a picture of the gray card. At first you might think 127 (half way between 0 and 255), but for sRGB, but I think it is 118 as given by the equation (1.055*x^(1/2.4)-0.055) * 255, where x is the normalized exposure, !8% or 0.18 for the gray card. See Norman Koren's web site for a good explanation of gamma, exposure, and monitor calibration. The equation in the box on Norman's site is the inverse gamma function for sRGB, going from pixel level in the file to the monitor. In the current case we must go from the reading of the sensor to the pixel level of the file.

http://www.normankoren.com/makingfineprints1A.html#Gammabox

Rather than taking numerous pictures of a gray card, you can get this information and more by photographing a Macbeth color checker chart and analyzing it with Imitest, an excellent and inexpensive program by Norman Koren.

http://www.imatest.com/

I did a series of analyses with Imitest on the color checker for the D70. To get proper exposure I took a reading from a gray card and increased the exposure by 0.5 f/stops. Then I took shots of the color checker at various exposures (based on the grey card reading + 1/2 stop) and processed them in Nikon Capture with a normal tone compensation and with Fotogenic's PS4 tone curve, which boosts the highlights the same as giving 0.5 stops more exposure.

The resulting photos and analyses are posted. The original files were in TIFF, but these are too large to post, so I saved them with jpeg.

http://bjanes.smugmug.com/gallery/377720

The gray card shot at the exposure indicated by the 18% gray card gave a pixel value of 100 with the normal tone curve, and the shot with 1/2 stop over the gray card reading gave 119, just where it should be. I then exposed the chart normally (grey card reading + 1/2 stop) and applied the PS4 tone curve in NC and compared the result to that of a normal tone compensation with a 1/2 stop positive exposure compensation (grey card reading +1 stop) as Fotogenic advised in a previous post.

The Imitest results are posted. For help in interpreting them see the Imitest web site. At first, they seem imposing, but the documentation makes it easy to interpret them. For example, look at the analysis of the gray squares on the target with normal exposure (1/2 stop over the grey card reading). The top left graph shows the pixel level for each black and white square on the target. The top right curve shows the characteristic curve.

http://bjanes.smugmug.com/gallery/377720/1/15066952/Large

Compare this to the half stop positive exposure compensation (MacbethPlusOne). The characteristic curve is very similar to the PS4 curve with normal exposure as Fotogenic says it should be. The white square (optical density of 0.05 on the target) is at pixel level 255 and any highlights over that would be blown with the positive compensation.

http://bjanes.smugmug.com/gallery/377720/2/15066956/Large

Peruse the other results on your own; this post is long enough already! I trial version of Imitest is available for free download at the web site and you can test it on the posted images (be sure to download them at their original sizes). Since the original anayses were on TIFFs, the results might not agree exactly. Here we are using only the Macbeth analysis portion of the program but it has other functions not mentioned here.

I have no financial interest in Imitest, but do recommend it highly.

--
Bill Janes

 

[Man-Fai Wong]

... turn us all into measurebators? ;-)

BTW, thanks for the efforts.

Man

I had originally entered into these discussions with the belief
that my D70 consistently underexposed images, but after reading the
postings by Fotogenic and others, I have come to the realization
that the D70's exposure is accurate, but that one must choose the
proper tone curve that one applies either in the camera in the jpeg
mode or in the NEF converter with raw files to get properly exposed
highlights. The purpose of this post is to compare Fotogenic's PS4
curve to the results of 0.5 stop positive exposure compensation
with Nikons Normal tone compensation (which he advised me to do in
earlier posting for a proper comparison) and to describe an easy
and quantitative method of doing so. I don't expect many responses
to this post, but it may interest a few.

Fotogenics analysis this matter is the best that I have seen on the
subject, and you should read it if you have not already done so:

http://fotogenetic.dearingfilm.com/custom_tone_curves.html

As he describes, you can photograph a gray card at various
exposures, bracketing around the exposure indcated by the light
meter for a particular ISO, and plot the pixel value in the
resulting picture to obtain the characteristic curve for those
conditions. This is the method used by Ansel Adams in his book The
Negative. The exposure that reproduces the pixel level of the gray
card is the proper one.

Actually, when using a gray card determine exosure, one should
increase the indicated exposure by 1/2 f/stop (0.5 EV). See Thom
Hogan's essay:

http://www.bythom.com/graycards.htm

What is the pixel level that one should get from taking a picture
of the gray card. At first you might think 127 (half way between 0
and 255), but for sRGB, but I think it is 118 as given by the
equation (1.055*x^(1/2.4)-0.055) * 255, where x is the normalized
exposure, !8% or 0.18 for the gray card. See Norman Koren's web
site for a good explanation of gamma, exposure, and monitor
calibration. The equation in the box on Norman's site is the
inverse gamma function for sRGB, going from pixel level in the file
to the monitor. In the current case we must go from the reading of
the sensor to the pixel level of the file.

http://www.normankoren.com/makingfineprints1A.html#Gammabox

Rather than taking numerous pictures of a gray card, you can get
this information and more by photographing a Macbeth color checker
chart and analyzing it with Imitest, an excellent and inexpensive
program by Norman Koren.

http://www.imatest.com/

I did a series of analyses with Imitest on the color checker for
the D70. To get proper exposure I took a reading from a gray card
and increased the exposure by 0.5 f/stops. Then I took shots of the
color checker at various exposures (based on the grey card reading
+ 1/2 stop) and processed them in Nikon Capture with a normal tone
compensation and with Fotogenic's PS4 tone curve, which boosts the
highlights the same as giving 0.5 stops more exposure.

The resulting photos and analyses are posted. The original files
were in TIFF, but these are too large to post, so I saved them with
jpeg.

http://bjanes.smugmug.com/gallery/377720

The gray card shot at the exposure indicated by the 18% gray card
gave a pixel value of 100 with the normal tone curve, and the shot
with 1/2 stop over the gray card reading gave 119, just where it
should be. I then exposed the chart normally (grey card reading +
1/2 stop) and applied the PS4 tone curve in NC and compared the
result to that of a normal tone compensation with a 1/2 stop
positive exposure compensation (grey card reading +1 stop) as
Fotogenic advised in a previous post.

The Imitest results are posted. For help in interpreting them see
the Imitest web site. At first, they seem imposing, but the
documentation makes it easy to interpret them. For example, look at
the analysis of the gray squares on the target with normal exposure
(1/2 stop over the grey card reading). The top left graph shows the
pixel level for each black and white square on the target. The top
right curve shows the characteristic curve.

http://bjanes.smugmug.com/gallery/377720/1/15066952/Large

Compare this to the half stop positive exposure compensation
(MacbethPlusOne). The characteristic curve is very similar to the
PS4 curve with normal exposure as Fotogenic says it should be. The
white square (optical density of 0.05 on the target) is at pixel
level 255 and any highlights over that would be blown with the
positive compensation.

http://bjanes.smugmug.com/gallery/377720/2/15066956/Large

Peruse the other results on your own; this post is long enough
already! I trial version of Imitest is available for free download
at the web site and you can test it on the posted images (be sure
to download them at their original sizes). Since the original
anayses were on TIFFs, the results might not agree exactly. Here we
are using only the Macbeth analysis portion of the program but it
has other functions not mentioned here.

I have no financial interest in Imitest, but do recommend it highly.

--
Bill Janes

--



Just another amateur learning to paint w/ 'the light of the world.' (John 8:12)
Motto for the season: 'Cameras are for making photos, not war...'
See my profile for more + some basic photog resources.
As usual, YMMV + caveat emptor.
Contact me at [email protected]
Indulge my fancies at http://www.pbase.com/mandnwong

 

[Bill Janes]

... turn us all into measurebators? ;-)

BTW, thanks for the efforts.

Man

Man,

Thank you for taking the time to respond and thank me. No, I don't think many would make the measurements, but we have had some pretty inaccurate statments on underesposure, some by me in my earlier posts. Anecdotal reprots based on experience or false reasoning can be pretty far off base. If you have actual data, you can speak with more certainty.

Fotogenics measurements are what got me started with my one and I have gained a much better appreciation of the topic and hopefully others can gain experience secondhand without doing measurements themselves.

So far you are the only one replying to this post; I did not expect many. Normal Koren told me that response from individual photographers to Imitest has been less than he expected, but that many big businesses werre buying the program and he underpriced it for this market.

--
Bill Janes

 

[Chris Sweet]

Bill,

Very interesting. A couple of things that I wanted to clarify. When you say +.5 EV PS4 does that mean that you used the curve AND .5EV or just the curve with 0EV resulting in .5EV?

I have not had the time to learn how to read the Imatest charts but there does appear to be some enhanced blue channel noise with the .5EV that isn't there with the PS4 curve. Or am I reading this wrong?

Do you have any final thoughts to sum up after having done the tests and studied the results?

Thanks for taking the time to do this thankless task. Eventually people will come looking for this information.

Chris Sweet

I had originally entered into these discussions with the belief
that my D70 consistently underexposed images, but after reading the
postings by Fotogenic and others, I have come to the realization
that the D70's exposure is accurate, but that one must choose the
proper tone curve that one applies either in the camera in the jpeg
mode or in the NEF converter with raw files to get properly exposed
highlights. The purpose of this post is to compare Fotogenic's PS4
curve to the results of 0.5 stop positive exposure compensation
with Nikons Normal tone compensation (which he advised me to do in
earlier posting for a proper comparison) and to describe an easy
and quantitative method of doing so. I don't expect many responses
to this post, but it may interest a few.

Fotogenics analysis this matter is the best that I have seen on the
subject, and you should read it if you have not already done so:

http://fotogenetic.dearingfilm.com/custom_tone_curves.html

As he describes, you can photograph a gray card at various
exposures, bracketing around the exposure indcated by the light
meter for a particular ISO, and plot the pixel value in the
resulting picture to obtain the characteristic curve for those
conditions. This is the method used by Ansel Adams in his book The
Negative. The exposure that reproduces the pixel level of the gray
card is the proper one.

Actually, when using a gray card determine exosure, one should
increase the indicated exposure by 1/2 f/stop (0.5 EV). See Thom
Hogan's essay:

http://www.bythom.com/graycards.htm

What is the pixel level that one should get from taking a picture
of the gray card. At first you might think 127 (half way between 0
and 255), but for sRGB, but I think it is 118 as given by the
equation (1.055*x^(1/2.4)-0.055) * 255, where x is the normalized
exposure, !8% or 0.18 for the gray card. See Norman Koren's web
site for a good explanation of gamma, exposure, and monitor
calibration. The equation in the box on Norman's site is the
inverse gamma function for sRGB, going from pixel level in the file
to the monitor. In the current case we must go from the reading of
the sensor to the pixel level of the file.

http://www.normankoren.com/makingfineprints1A.html#Gammabox

Rather than taking numerous pictures of a gray card, you can get
this information and more by photographing a Macbeth color checker
chart and analyzing it with Imitest, an excellent and inexpensive
program by Norman Koren.

http://www.imatest.com/

I did a series of analyses with Imitest on the color checker for
the D70. To get proper exposure I took a reading from a gray card
and increased the exposure by 0.5 f/stops. Then I took shots of the
color checker at various exposures (based on the grey card reading
+ 1/2 stop) and processed them in Nikon Capture with a normal tone
compensation and with Fotogenic's PS4 tone curve, which boosts the
highlights the same as giving 0.5 stops more exposure.

The resulting photos and analyses are posted. The original files
were in TIFF, but these are too large to post, so I saved them with
jpeg.

http://bjanes.smugmug.com/gallery/377720

The gray card shot at the exposure indicated by the 18% gray card
gave a pixel value of 100 with the normal tone curve, and the shot
with 1/2 stop over the gray card reading gave 119, just where it
should be. I then exposed the chart normally (grey card reading +
1/2 stop) and applied the PS4 tone curve in NC and compared the
result to that of a normal tone compensation with a 1/2 stop
positive exposure compensation (grey card reading +1 stop) as
Fotogenic advised in a previous post.

The Imitest results are posted. For help in interpreting them see
the Imitest web site. At first, they seem imposing, but the
documentation makes it easy to interpret them. For example, look at
the analysis of the gray squares on the target with normal exposure
(1/2 stop over the grey card reading). The top left graph shows the
pixel level for each black and white square on the target. The top
right curve shows the characteristic curve.

http://bjanes.smugmug.com/gallery/377720/1/15066952/Large

Compare this to the half stop positive exposure compensation
(MacbethPlusOne). The characteristic curve is very similar to the
PS4 curve with normal exposure as Fotogenic says it should be. The
white square (optical density of 0.05 on the target) is at pixel
level 255 and any highlights over that would be blown with the
positive compensation.

http://bjanes.smugmug.com/gallery/377720/2/15066956/Large

Peruse the other results on your own; this post is long enough
already! I trial version of Imitest is available for free download
at the web site and you can test it on the posted images (be sure
to download them at their original sizes). Since the original
anayses were on TIFFs, the results might not agree exactly. Here we
are using only the Macbeth analysis portion of the program but it
has other functions not mentioned here.

I have no financial interest in Imitest, but do recommend it highly.

--
Bill Janes

 

[jnarciso]

(nt)

 

[Bill Janes]

Chris,

Bill,

Very interesting. A couple of things that I wanted to clarify. When
you say +.5 EV PS4 does that mean that you used the curve AND .5EV
or just the curve with 0EV resulting in .5EV?

Yes, +0.5 EV means 1/2 stop more than the gray card reading, which is the normal exposure. As I understand it, Fotogenic's PS4 curve applies another 0.5 EV to the highlights for a total boost of one stop. This is why Fotogenic said the curve should be compared to a normal exposure +0.5EV, which would be 1 stop over the gray card reading, or plus one in my scheme.

I have not had the time to learn how to read the Imatest charts but
there does appear to be some enhanced blue channel noise with the
.5EV that isn't there with the PS4 curve. Or am I reading this
wrong?

With regard to noise, I haven't been working with this much either, but it appears to me that the curve redistributes the noise. It is lower in zone 1 with the curve than with normal exposure, but higher in zone 5. The average noise levels are about the same.

Of course the noise is lower with 0.5EV over normal exposure (plus one over the gray card) but there is danger of blowing the highlights and you have to use a lower shuttter speed, which you do not want to do with available light shooting. See the posts by John Friend.

Do you have any final thoughts to sum up after having done the
tests and studied the results?

Not yet. Imitest has another mode to ananyze a Q15 gray scale, which gives a more detailed analysis. This one is from some MTF testing I was doing on my kit lens (I did not apply the PS4 curve, since I didn't even know about it then). I don't think Fotogenic designed the curve with noise in mind, but I don't think that it is a significant problem.

http://bjanes.smugmug.com/gallery/377720/2/15189401

Thanks for taking the time to do this thankless task. Eventually
people will come looking for this information.

Chris Sweet

Bill Janes

 

[desmobob]

Great info... thanks Bill.

Good shooting,
Bob Scott

 

[Chris Sweet]

Bill,

I have been following Photogenic's posts quite carefully and maybe I'm not understanding something. I was under the impression that the two main curves (EV3 & PS) were a SUBSITUTE for using either +.3 OR +.5EV. NOT to be used in conjunction with +EV compensation (which would result as you mentioned in +.6 or +1.0EV). Now I may be wrong, and we may get Photogenic to chime in here at some point, but the impression I was left with is that the curves give you the effect of the +EV without using the +EV. Resulting in opening up the mid tones and ameliorating the nasty appearence of blown highlights by squeezing them into the last 1/2 stop so they don't appear so harsh and can be recovered better in post if need be.

Again I may be wrong here and again I would like to thank you for providing the information from your tests to the rest of us looking for that "perfect" exposure.

Chris

Bill,

Very interesting. A couple of things that I wanted to clarify. When
you say +.5 EV PS4 does that mean that you used the curve AND .5EV
or just the curve with 0EV resulting in .5EV?

Yes, +0.5 EV means 1/2 stop more than the gray card reading, which
is the normal exposure. As I understand it, Fotogenic's PS4 curve
applies another 0.5 EV to the highlights for a total boost of one
stop. This is why Fotogenic said the curve should be compared to a
normal exposure +0.5EV, which would be 1 stop over the gray card
reading, or plus one in my scheme.

I have not had the time to learn how to read the Imatest charts but
there does appear to be some enhanced blue channel noise with the
.5EV that isn't there with the PS4 curve. Or am I reading this
wrong?

With regard to noise, I haven't been working with this much either,
but it appears to me that the curve redistributes the noise. It is
lower in zone 1 with the curve than with normal exposure, but
higher in zone 5. The average noise levels are about the same.

Of course the noise is lower with 0.5EV over normal exposure (plus
one over the gray card) but there is danger of blowing the
highlights and you have to use a lower shuttter speed, which you do
not want to do with available light shooting. See the posts by John
Friend.

Do you have any final thoughts to sum up after having done the
tests and studied the results?

Not yet. Imitest has another mode to ananyze a Q15 gray scale,
which gives a more detailed analysis. This one is from some MTF
testing I was doing on my kit lens (I did not apply the PS4 curve,
since I didn't even know about it then). I don't think Fotogenic
designed the curve with noise in mind, but I don't think that it is
a significant problem.

http://bjanes.smugmug.com/gallery/377720/2/15189401

Thanks for taking the time to do this thankless task. Eventually
people will come looking for this information.

Chris Sweet

Bill Janes

 

[Paul*H]

Dear Bill,

Fotogenetic's work on this subject is fantastic, and his knowledge of the D70/D100 camera and its characteristics astonishing. Equally amazing is your information, research, and putting theories to the test. Thanks for all the hard work you have done, to "validate" all information on this subject. I had also experienced the "underexposure phenomenon" and did much research and testing of my own, although not as scientifically as you have shown. I have gained a lot of knowledge from reading your posts and links, and also the information from Fotogenetics site. This information can be utilized for just about any camera, as it covers the fundamentals of exposure, and how to overcome certain issues.

Thanks again for your hard work and validation, and I am sure many people will benefit from your post.
Cheers,
Paul.

 

[scottinlex]

I have been using fotogenics curves in both my D100 and D70, and both of them still

REQUIRE a bump of between +.3 and +.7 exposure compensation. the last wedding I shot

with the D70, i used the latest curve, and all images had to be adjusted in NC4 by
nearly a stop to make them right. I may have to do some more experimenting, but
the results, at least to me, are better with both.

 

[photomarco]

Thanks Bill for this amazing work.
Bookmarked, to be understood later

Marco

I had originally entered into these discussions with the belief
that my D70 consistently underexposed images, but after reading the
postings by Fotogenic and others, I have come to the realization
that the D70's exposure is accurate, but that one must choose the
proper tone curve that one applies either in the camera in the jpeg
mode or in the NEF converter with raw files to get properly exposed
highlights. The purpose of this post is to compare Fotogenic's PS4
curve to the results of 0.5 stop positive exposure compensation
with Nikons Normal tone compensation (which he advised me to do in
earlier posting for a proper comparison) and to describe an easy
and quantitative method of doing so. I don't expect many responses
to this post, but it may interest a few.

Fotogenics analysis this matter is the best that I have seen on the
subject, and you should read it if you have not already done so:

http://fotogenetic.dearingfilm.com/custom_tone_curves.html

As he describes, you can photograph a gray card at various
exposures, bracketing around the exposure indcated by the light
meter for a particular ISO, and plot the pixel value in the
resulting picture to obtain the characteristic curve for those
conditions. This is the method used by Ansel Adams in his book The
Negative. The exposure that reproduces the pixel level of the gray
card is the proper one.

Actually, when using a gray card determine exosure, one should
increase the indicated exposure by 1/2 f/stop (0.5 EV). See Thom
Hogan's essay:

http://www.bythom.com/graycards.htm

What is the pixel level that one should get from taking a picture
of the gray card. At first you might think 127 (half way between 0
and 255), but for sRGB, but I think it is 118 as given by the
equation (1.055*x^(1/2.4)-0.055) * 255, where x is the normalized
exposure, !8% or 0.18 for the gray card. See Norman Koren's web
site for a good explanation of gamma, exposure, and monitor
calibration. The equation in the box on Norman's site is the
inverse gamma function for sRGB, going from pixel level in the file
to the monitor. In the current case we must go from the reading of
the sensor to the pixel level of the file.

http://www.normankoren.com/makingfineprints1A.html#Gammabox

Rather than taking numerous pictures of a gray card, you can get
this information and more by photographing a Macbeth color checker
chart and analyzing it with Imitest, an excellent and inexpensive
program by Norman Koren.

http://www.imatest.com/

I did a series of analyses with Imitest on the color checker for
the D70. To get proper exposure I took a reading from a gray card
and increased the exposure by 0.5 f/stops. Then I took shots of the
color checker at various exposures (based on the grey card reading
+ 1/2 stop) and processed them in Nikon Capture with a normal tone
compensation and with Fotogenic's PS4 tone curve, which boosts the
highlights the same as giving 0.5 stops more exposure.

The resulting photos and analyses are posted. The original files
were in TIFF, but these are too large to post, so I saved them with
jpeg.

http://bjanes.smugmug.com/gallery/377720

The gray card shot at the exposure indicated by the 18% gray card
gave a pixel value of 100 with the normal tone curve, and the shot
with 1/2 stop over the gray card reading gave 119, just where it
should be. I then exposed the chart normally (grey card reading +
1/2 stop) and applied the PS4 tone curve in NC and compared the
result to that of a normal tone compensation with a 1/2 stop
positive exposure compensation (grey card reading +1 stop) as
Fotogenic advised in a previous post.

The Imitest results are posted. For help in interpreting them see
the Imitest web site. At first, they seem imposing, but the
documentation makes it easy to interpret them. For example, look at
the analysis of the gray squares on the target with normal exposure
(1/2 stop over the grey card reading). The top left graph shows the
pixel level for each black and white square on the target. The top
right curve shows the characteristic curve.

http://bjanes.smugmug.com/gallery/377720/1/15066952/Large

Compare this to the half stop positive exposure compensation
(MacbethPlusOne). The characteristic curve is very similar to the
PS4 curve with normal exposure as Fotogenic says it should be. The
white square (optical density of 0.05 on the target) is at pixel
level 255 and any highlights over that would be blown with the
positive compensation.

http://bjanes.smugmug.com/gallery/377720/2/15066956/Large

Peruse the other results on your own; this post is long enough
already! I trial version of Imitest is available for free download
at the web site and you can test it on the posted images (be sure
to download them at their original sizes). Since the original
anayses were on TIFFs, the results might not agree exactly. Here we
are using only the Macbeth analysis portion of the program but it
has other functions not mentioned here.

I have no financial interest in Imitest, but do recommend it highly.

--
Bill Janes

 

[Bill Janes]

Chris,

As I understand it, you are correct. The gray card reading +0.5 EV is normal exposure because light meters are not really calibrated to the gray card reading as most of us have thought in the past. Fotogenics PS4 curve, I think, is not to be used with any exposure compensation. Fotogenic is a naval officer and is deployed at times and is unable to make posts. I would like to hear from him too.

The following is quoted from Thom Hogans website and may help explain the situation. I wish I had used different nomenclature in my post.

http://www.bythom.com/graycards.htm

"ANSI standards (which, unfortunately, are not publically published--you have to pay big bucks to have access to them), calibrate meters using luminance, not reflection. For an ANSI calibrated meter, the most commonly published information I've seen is that the luminance value used translates into a reflectance of 12%. I've also seen 12.5% and 13% (so where the heck does Sekonic's 14% come from?), but 12% seems to be correct--one half stop lighter than 18%, by the way. I haven't seen anyone claim that ANSI calibration translates into a reflectance of 18%.

So, there are two questions that need to be asked (and of engineers at Nikon that would know of what we speak, not the Nikon USA folk who read translated documentation and learned from the same Photography 101 books we did):

1. Does Nikon calibrate its meters to ANSI standards? (My previous conversations with Nikon engineers leads me to believe the answer is yes.)

2. Would you need a 12% gray card to get the correct exposure using an ANSI calibrated meter (i.e., is the luminance setting for ANSI really equivalent to 12% reflectance?)? (I believe the answer is again yes, but we can make do with 18% gray cards. Simply take a reading with the card angled between the lens axis and light source, then open up 1/2 stop.) "

Bill Janes

 

[Bill Janes]

Paul,

Thanks for the compliment, but I'm hardly in the same league as Fotogenic. I had to do these tests for myself to understand what he was doing.

Bill

Dear Bill,
Fotogenetic's work on this subject is fantastic, and his knowledge
of the D70/D100 camera and its characteristics astonishing. Equally
amazing is your information, research, and putting theories to the
test. Thanks for all the hard work you have done, to "validate" all
information on this subject. I had also experienced the
"underexposure phenomenon" and did much research and testing of my
own, although not as scientifically as you have shown. I have
gained a lot of knowledge from reading your posts and links, and
also the information from Fotogenetics site. This information can
be utilized for just about any camera, as it covers the
fundamentals of exposure, and how to overcome certain issues.
Thanks again for your hard work and validation, and I am sure many
people will benefit from your post.
Cheers,
Paul.

 

[eneiman]

I had originally entered into these discussions with the belief
that my D70 consistently underexposed images, but after reading the
postings by Fotogenic and others, I have come to the realization
that the D70's exposure is accurate, but that one must choose the
proper tone curve that one applies either in the camera in the jpeg
mode or in the NEF converter with raw files to get properly exposed
highlights. The purpose of this post is to compare Fotogenic's PS4
curve to the results of 0.5 stop positive exposure compensation
with Nikons Normal tone compensation (which he advised me to do in
earlier posting for a proper comparison) and to describe an easy
and quantitative method of doing so. I don't expect many responses
to this post, but it may interest a few.

Fotogenics analysis this matter is the best that I have seen on the
subject, and you should read it if you have not already done so:

http://fotogenetic.dearingfilm.com/custom_tone_curves.html

As he describes, you can photograph a gray card at various
exposures, bracketing around the exposure indcated by the light
meter for a particular ISO, and plot the pixel value in the
resulting picture to obtain the characteristic curve for those
conditions. This is the method used by Ansel Adams in his book The
Negative. The exposure that reproduces the pixel level of the gray
card is the proper one.

Actually, when using a gray card determine exosure, one should
increase the indicated exposure by 1/2 f/stop (0.5 EV). See Thom
Hogan's essay:

http://www.bythom.com/graycards.htm

What is the pixel level that one should get from taking a picture
of the gray card. At first you might think 127 (half way between 0
and 255), but for sRGB, but I think it is 118 as given by the
equation (1.055*x^(1/2.4)-0.055) * 255, where x is the normalized
exposure, !8% or 0.18 for the gray card. See Norman Koren's web
site for a good explanation of gamma, exposure, and monitor
calibration. The equation in the box on Norman's site is the
inverse gamma function for sRGB, going from pixel level in the file
to the monitor. In the current case we must go from the reading of
the sensor to the pixel level of the file.

http://www.normankoren.com/makingfineprints1A.html#Gammabox

Rather than taking numerous pictures of a gray card, you can get
this information and more by photographing a Macbeth color checker
chart and analyzing it with Imitest, an excellent and inexpensive
program by Norman Koren.

http://www.imatest.com/

I did a series of analyses with Imitest on the color checker for
the D70. To get proper exposure I took a reading from a gray card
and increased the exposure by 0.5 f/stops. Then I took shots of the
color checker at various exposures (based on the grey card reading
+ 1/2 stop) and processed them in Nikon Capture with a normal tone
compensation and with Fotogenic's PS4 tone curve, which boosts the
highlights the same as giving 0.5 stops more exposure.

The resulting photos and analyses are posted. The original files
were in TIFF, but these are too large to post, so I saved them with
jpeg.

http://bjanes.smugmug.com/gallery/377720

The gray card shot at the exposure indicated by the 18% gray card
gave a pixel value of 100 with the normal tone curve, and the shot
with 1/2 stop over the gray card reading gave 119, just where it
should be. I then exposed the chart normally (grey card reading +
1/2 stop) and applied the PS4 tone curve in NC and compared the
result to that of a normal tone compensation with a 1/2 stop
positive exposure compensation (grey card reading +1 stop) as
Fotogenic advised in a previous post.

The Imitest results are posted. For help in interpreting them see
the Imitest web site. At first, they seem imposing, but the
documentation makes it easy to interpret them. For example, look at
the analysis of the gray squares on the target with normal exposure
(1/2 stop over the grey card reading). The top left graph shows the
pixel level for each black and white square on the target. The top
right curve shows the characteristic curve.

http://bjanes.smugmug.com/gallery/377720/1/15066952/Large

Compare this to the half stop positive exposure compensation
(MacbethPlusOne). The characteristic curve is very similar to the
PS4 curve with normal exposure as Fotogenic says it should be. The
white square (optical density of 0.05 on the target) is at pixel
level 255 and any highlights over that would be blown with the
positive compensation.

http://bjanes.smugmug.com/gallery/377720/2/15066956/Large

Peruse the other results on your own; this post is long enough
already! I trial version of Imitest is available for free download
at the web site and you can test it on the posted images (be sure
to download them at their original sizes). Since the original
anayses were on TIFFs, the results might not agree exactly. Here we
are using only the Macbeth analysis portion of the program but it
has other functions not mentioned here.

I have no financial interest in Imitest, but do recommend it highly.

--
Bill Janes

--
Steven, from Canada

 

[Laslo Varadi]

I have the same experience. I have to use the +.3 or .7 EV and the Fotogenic P&S curve.

Laslo

I have been using fotogenics curves in both my D100 and D70, and
both of them still
REQUIRE a bump of between +.3 and +.7 exposure compensation. the
last wedding I shot
with the D70, i used the latest curve, and all images had to be
adjusted in NC4 by
nearly a stop to make them right. I may have to do some more
experimenting, but
the results, at least to me, are better with both.

--
lv1

 

[casey81696]

This is a sensible message

 

[geneinphx]

Bill,

Thanks for all the marvelous info you've provided!!!!!!!!!!!

I’ve followed your postings recently on the underexposure tendency on the D70. As any D70 user generally finds out early is that this camera does indeed underexpose for the purpose of not blowing the highlights.

You’ve taken quite a journey it seems this past week so I’m no curious to find out if your opinion on this has changed. Not that I am certain, but it seemed like you were definitely of the opinion that this camera underexposed when you started. What is your opinion now?

FWIW, I’ve come to the strong opinion that out of the box it should by default expose more aggressively to the right. Let’s admit this camera in particular is Nikon’s absolute bottom of the line DSLR so a lot of newbies are going to have difficulty with no clue as to why their pictures are dim. I have found that blowing the highlights (as long as it’s not too bad) now and then isn’t such a big issue in many photos I take. An “expert” it would seem to me might know immediately that they might want to back off and change the defaults to expose more to the left.

Gene

 

[Man-Fai Wong]

Other than the mention of a wedding, there's no mention of what these shots are that require the + exp comp on top of the curve.

For wedding, if you're shooting the bride w/ her white gown covering a large part of the frame and normal kind of scene, you should expect to apply some + exp comp due to the white dress much like in your average snow scene -- this is assuming matrix metering. +.3 or +.7 sounds reasonable. If you're using flash, the flash metering might be an issue also.

An accurate (and precise) meter does not mean you never need to apply some exp comp. It just means that you can know what to expect. It's just a tool.

Man

Laslo

I have been using fotogenics curves in both my D100 and D70, and
both of them still
REQUIRE a bump of between +.3 and +.7 exposure compensation. the
last wedding I shot
with the D70, i used the latest curve, and all images had to be
adjusted in NC4 by
nearly a stop to make them right. I may have to do some more
experimenting, but
the results, at least to me, are better with both.

--
lv1

--



Just another amateur learning to paint w/ 'the light of the world.' (John 8:12)
Motto for the season: 'Cameras are for making photos, not war...'
See my profile for more + some basic photog resources.
As usual, YMMV + caveat emptor.
Contact me at [email protected]
Indulge my fancies at http://www.pbase.com/mandnwong

 

[Chris Sweet]

Bill,

Thanks for clearing this up. So in your tests when you say +1EV you are refering to the curve with +.5 EV added right?

I had read that stuff by Thom awhile ago when I started using full manual mode and spot metering almost exclusivly. I decided that no matter how good the Nikon Matrix meter is I really needed to learn how to do it myself . Forcing yourself to do it this way sometimes will give you an appreaciation for how good Matrix is and when it will most likely be wrong. For me the answer is RAW with EV3 and watch the histogram.

Chris

Chris,

As I understand it, you are correct. The gray card reading +0.5 EV
is normal exposure because light meters are not really calibrated
to the gray card reading as most of us have thought in the past.
Fotogenics PS4 curve, I think, is not to be used with any exposure
compensation. Fotogenic is a naval officer and is deployed at times
and is unable to make posts. I would like to hear from him too.

The following is quoted from Thom Hogans website and may help
explain the situation. I wish I had used different nomenclature in
my post.

http://www.bythom.com/graycards.htm

"ANSI standards (which, unfortunately, are not publically
published--you have to pay big bucks to have access to them),
calibrate meters using luminance, not reflection. For an ANSI
calibrated meter, the most commonly published information I've seen
is that the luminance value used translates into a reflectance of
12%. I've also seen 12.5% and 13% (so where the heck does Sekonic's
14% come from?), but 12% seems to be correct--one half stop lighter
than 18%, by the way. I haven't seen anyone claim that ANSI
calibration translates into a reflectance of 18%.

So, there are two questions that need to be asked (and of engineers
at Nikon that would know of what we speak, not the Nikon USA folk
who read translated documentation and learned from the same
Photography 101 books we did):

1. Does Nikon calibrate its meters to ANSI standards? (My previous
conversations with Nikon engineers leads me to believe the answer
is yes.)
2. Would you need a 12% gray card to get the correct exposure using
an ANSI calibrated meter (i.e., is the luminance setting for ANSI
really equivalent to 12% reflectance?)? (I believe the answer is
again yes, but we can make do with 18% gray cards. Simply take a
reading with the card angled between the lens axis and light
source, then open up 1/2 stop.) "

Bill Janes

 

[CWilt]

Just curious which color mode you used for these tests? It appears to me on the histogram that aRGB has about more room in the highlights and less in the shadows which also shifts the midtones. I have not tried to measure the differnce between aRGB and sRGB.

Try shooting an 18% card manually in mode I and mode II. Compare the histograms between the two. You should see that peak moves up or down depending on which color mode was used.
--
http://stakeman.smugmug.com