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Critical color correction, can PS do this?

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Ranjan

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I ran into a critical color correction problem where I found that PS is not able to do a perfect job.

I shot a color target from profile prism & wanted to create a correction which can be applied to all the shots of carpets shot in the same light. The target has a row of netural patches in lower. PS cannot do all the patches netural by any methods, I tried levels, varitions, curves, selective color, additional plugins, finally I found that Edit lab can do it much better correction of all the patches.

I feel PS does not have perfect answer to this, I may be wrong but cannot find a method to to the following.

I shoot a series of grey patches from white to black with my studio flash, the grey patches show unequal RGB numbers, I want to neturalize all the patches with equal RGB values ie: 10.10.10/ 50.50.50. 80.80.80. & so on till 255.255.255.
I cannot find any such method via any tools to do so.
Edit lab did it 90% correctly but not 100%.
Can anyone tell me how to to this in PS7 CS

--
Ranjan
Professional photographer.
http://www.photosig.com/go/users/view?id=11993
 
Have you tried going to Levels and then choosing the middle eyedropper and clicking the gray patches in your photo. The middle eyedropper sets the gray to neutral the right is for white and the left is for setting the black. HTH

David
 
When you say you "shot" the target, what did you shoot it with? Film, digital?

If digital, is the camera profiled & custom white balanced to your light source? If film, is the film properly color balanced to your light source & checked?

I would say almost certainly that it is not a Photoshop issue. It's probably more a "Ranjan" issue.

BTW, when shooting your carpet samples, be aware that many color dyes used in carpet/fabric manufacturing, natural or synthetic, utilize UV birghtners, which will give you headaches trying to color match, if you have a UV (uncorrected strobe/flash for sure) issue going on.
Best of luck,
Kevin Logan
Ranjan said:
I ran into a critical color correction problem where I found that
PS is not able to do a perfect job.

I shot a color target from profile prism & wanted to create a
correction which can be applied to all the shots of carpets shot in
the same light. The target has a row of netural patches in lower.
PS cannot do all the patches netural by any methods, I tried
levels, varitions, curves, selective color, additional plugins,
finally I found that Edit lab can do it much better correction of
all the patches.

I feel PS does not have perfect answer to this, I may be wrong but
cannot find a method to to the following.
I shoot a series of grey patches from white to black with my studio
flash, the grey patches show unequal RGB numbers, I want to
neturalize all the patches with equal RGB values ie: 10.10.10/
50.50.50. 80.80.80. & so on till 255.255.255.
I cannot find any such method via any tools to do so.
Edit lab did it 90% correctly but not 100%.
Can anyone tell me how to to this in PS7 CS

--
Ranjan
Professional photographer.
http://www.photosig.com/go/users/view?id=11993
Click to expand...
--
Kevin Logan
http://kevinlogan.com
 
Hi Ranjan,

As long as your neutral patches are "in the ballpark" they can be corrected perfectly in Photoshop using curves. Here's an example of how to do it:

Let's say your darkest patch reads:

Red: 28
Green: 37
Blue: 16

And let's say you want to correct all three values to 32. Select the Red curve, click to place a point on the curve near the bottom. In the "Input" window type 28. In the output window type 32. While you're on the red curve, add additional points for each patch you want to correct, and type in the values. Then do the same for the green and blue curves. You'll have perfectly neutral patches.

However, this won't assure you of getting perfect color when shooting your carpets. It's a good start, but there are other variables, and you'll probably have to tweak.

Good luck,

-john
Ranjan said:
I ran into a critical color correction problem where I found that
PS is not able to do a perfect job.

I shot a color target from profile prism & wanted to create a
correction which can be applied to all the shots of carpets shot in
the same light. The target has a row of netural patches in lower.
PS cannot do all the patches netural by any methods, I tried
levels, varitions, curves, selective color, additional plugins,
finally I found that Edit lab can do it much better correction of
all the patches.

I feel PS does not have perfect answer to this, I may be wrong but
cannot find a method to to the following.
I shoot a series of grey patches from white to black with my studio
flash, the grey patches show unequal RGB numbers, I want to
neturalize all the patches with equal RGB values ie: 10.10.10/
50.50.50. 80.80.80. & so on till 255.255.255.
I cannot find any such method via any tools to do so.
Edit lab did it 90% correctly but not 100%.
Can anyone tell me how to to this in PS7 CS

--
Ranjan
Professional photographer.
http://www.photosig.com/go/users/view?id=11993
Click to expand...
 
SnapJack said:
The middle
eyedropper sets the gray to neutral the right is for white and the
left is for setting the black. HTH

David
Click to expand...
Yes my problem is that when I klik a patch & it gets converted to 128 128 128, the other patches dont follow the same route & there is no such facility in PS to address this.

How can I make a patch of which I know the value for sure is 50 50 50, but when photographed it shows the value 43 54 39, I know that its having a cast, & I have tried all the methods known to me for correcting but even I get close with one patch, my correction is not effecting the entire row in the same manner.
--
Ranjan
Professional photographer.
http://www.photosig.com/go/users/view?id=11993
 
kevin logan said:
When you say you "shot" the target, what did you shoot it with?
Film, digital?
If digital, is the camera profiled & custom white balanced to your
light source? If film, is the film properly color balanced to your
light source & checked?
Click to expand...
The shot is taken with D60 RAW converted & assigned a custom profile made with profile prism (hence the same target) white balanced using the grey card.
kevin logan said:
I would say almost certainly that it is not a Photoshop issue.
It's probably more a "Ranjan" issue.
Click to expand...
I will be glad to accept it as Ranjan's issue, thats why I am here that atleast I cannot find any solution to it in PS without a plugin. Edit lab does the required job 90% but wondering why not 100%.

May be I am going wrong somwhere, need help badly as I have spent over 15 hrs with 2 color specilist. We collectivelly have not been able to find a soloution.
kevin logan said:
BTW, when shooting your carpet samples, be aware that many color
dyes used in carpet/fabric manufacturing, natural or synthetic,
utilize UV birghtners, which will give you headaches trying to
color match, if you have a UV (uncorrected strobe/flash for sure)
issue going on.
Click to expand...
I was aware of this prior to shoot hence the custom profile & the target was shot, we are not going to do any correction for the carpet colors due to the very same reason as u have mentioned, but I cannot get my target shot nearly netural inspite a good WB was acheived.

Try to under stand my 128 128 128(grey) is perfectly 128 128 128, but I myself am surprised then why is the that my 50. 50. 50 & other patches are not perfect.
--
Ranjan
Professional photographer.
http://www.photosig.com/go/users/view?id=11993
 
Hi Ranjan,,

I would say it's probably your camera profile then. Profile Prism isn't bad, but far from great.

No matter what profiling software you use though, I doubt that you'll ever get a perfect profile, perfect enough so that a multi-step grey-scale will photograph perfectly neutral, i.e. yielding x,x,x equal values for RGB, across the whole scale from black to white.

Photoshop will, as you know, correct one patch perfectly, but then the others will be off, not because of Photoshop though, but because of what is going into photoshop, in terms of the file you're producing of the target with the camera.

Sounds like you almost want to create your own color space, something I guess is possible, but I wouldn't have a clue on that one. Sorry.
Hope you work it out though, to at least a reasonable degree for your needs.
All the best,
Kevin Logan
Ranjan said:
kevin logan said:
When you say you "shot" the target, what did you shoot it with?
Film, digital?
If digital, is the camera profiled & custom white balanced to your
light source? If film, is the film properly color balanced to your
light source & checked?
Click to expand...
The shot is taken with D60 RAW converted & assigned a custom
profile made with profile prism (hence the same target) white
balanced using the grey card.
Member said:
I would say almost certainly that it is not a Photoshop issue.
It's probably more a "Ranjan" issue.
Click to expand...
I will be glad to accept it as Ranjan's issue, thats why I am here
that atleast I cannot find any solution to it in PS without a
plugin. Edit lab does the required job 90% but wondering why not
100%.
May be I am going wrong somwhere, need help badly as I have spent
over 15 hrs with 2 color specilist. We collectivelly have not been
able to find a soloution.
Member said:
BTW, when shooting your carpet samples, be aware that many color
dyes used in carpet/fabric manufacturing, natural or synthetic,
utilize UV birghtners, which will give you headaches trying to
color match, if you have a UV (uncorrected strobe/flash for sure)
issue going on.
Click to expand...
I was aware of this prior to shoot hence the custom profile & the
target was shot, we are not going to do any correction for the
carpet colors due to the very same reason as u have mentioned, but
I cannot get my target shot nearly netural inspite a good WB was
acheived.

Try to under stand my 128 128 128(grey) is perfectly 128 128 128,
but I myself am surprised then why is the that my 50. 50. 50 &
other patches are not perfect.
--
Ranjan
Professional photographer.
http://www.photosig.com/go/users/view?id=11993
Click to expand...
--
Kevin Logan
http://kevinlogan.com
 
kevin logan said:
Hi Ranjan,,

I would say it's probably your camera profile then. Profile Prism
isn't bad, but far from great.
Click to expand...
I do understand that & feel that my generated profile may not be good enough, but PPrism reported to be excelent WB & target accuracy.

Lets say I strip my profile & assign & work in aRGB, even then the problem remans same.
kevin logan said:
No matter what profiling software you use though, I doubt that
you'll ever get a perfect profile, perfect enough so that a
multi-step grey-scale will photograph perfectly neutral, i.e.
yielding x,x,x equal values for RGB, across the whole scale from
black to white.
Click to expand...
It seems that PS correction are not linear(if I understand the term correctly) but Editlab plugin work better to do the same job in PS, which means that is possible, but wonder how perfectly this can be done & by which method.

BTW I like the website you have, will see it later using faster connection.
--
Ranjan
Professional photographer.
http://www.photosig.com/go/users/view?id=11993
 
John Adler said:
Hi Ranjan,

As long as your neutral patches are "in the ballpark" they can be
corrected perfectly in Photoshop using curves. Here's an example of
how to do it:

Let's say your darkest patch reads:

Red: 28
Green: 37
Blue: 16

And let's say you want to correct all three values to 32. Select
the Red curve, click to place a point on the curve near the bottom.
In the "Input" window type 28. In the output window type 32. While
you're on the red curve, add additional points for each patch you
want to correct, and type in the values. Then do the same for the
green and blue curves. You'll have perfectly neutral patches.
Click to expand...
Thanks John for your method, we tried using a similar method, by placing points on different patches (ctrl+click) in the curve window but soon loose control over the correction.

I will try to post a sample image for making everyone understand the problem, hope you can try this at your end.
Regards
--
Ranjan
Professional photographer.
http://www.photosig.com/go/users/view?id=11993
 
--

My comment is the same as John's. With the additions of reminding you that in Photoshop you are mesuring with the Info palatte the color shifts of your capture. The difference of what a 25/25/25 dark target now mesures vs. what it should be.

This is what I would do, after opening the test file in the same color scpace as the raw coverter was set or assingned for the output color space in PS, enter into Curves through Adjustment Layer... with the Info Palette opened,....

starting with the darkest value, the cursor over this spot will mesure the RGB values and the Info Palette will display it. Without moving the cursor,

Control/Shift/Click will "mesure" the RGB (brightness values) as well as the individual R,G,B, values...with Control/Click the mesured values will be placed on the 4 individual chanels, as you navigate with the keybord,

~ for RGB, 1 for Red, 2 for Green and 3 for Yellow... each curve will have the mesured value active on the curve, so with the up or down arrow you can add or remove values as needed.

Up to this point no brain work has been involved or typing numbers... Ps was just doing what it was designed to do... map original brightness values along with individual R,G,B, values.

The slight brain work necessary for correction, engaged at this point only becouse you have to decide how to adjust the individual R,G,B, values placed on the individual curves. If only one value is out, well... if all values are different or two are out... you will need to back track and look and mesure a lighter value so you can judge better the color shifts.

By Control clicking on the value placed on the curve the anchor piont can be removed.

Once you neutralised the color shift the values placed in the composit RGB chanel will allow correction of the over all brightness of the image, or if you know the original brightness value of the test targets after color adjustments... navigating through the individual color channels, the keybord command~ will bring you back to the composit RGB channel, here a mapped brightness value can be raised or lowered to the known original value, 20 is the mesured and neutralised value, but the "original" value was 25, well with ~ you are back in the composite RGB, so with the up arrow move up the mapped 20 value to 25...

You will have to do these steps ... mesure, place values, correct in individual RGB channels, with the last step befoe moving to the next graypatch (~ in composit RGB) adjust the brightness value... Next...Save the curve adjustment.

Start a new Action set, start recording and open next image, apply saved curve correction, save and close. Apply this action to a folder of images needed correction.
Simple as borscht. Please send money!
Best

Tony K
 
Iusefilm said:
--
My comment is the same as John's. With the additions of reminding
you that in Photoshop you are mesuring with the Info palatte the
color shifts of your capture. The difference of what a 25/25/25
dark target now mesures vs. what it should be.
This is what I would do, after opening the test file in the same
color scpace as the raw coverter was set or assingned for the
output color space in PS, enter into Curves through Adjustment
Layer... with the Info Palette opened,....
starting with the darkest value, the cursor over this spot will
mesure the RGB values and the Info Palette will display it. Without
moving the cursor,
Control/Shift/Click will "mesure" the RGB (brightness values) as
well as the individual R,G,B, values...with Control/Click the
mesured values will be placed on the 4 individual chanels, as you
navigate with the keybord,

~ for RGB, 1 for Red, 2 for Green and 3 for Yellow... each curve will have the mesured value active on the curve, so with the up or down arrow you can add or remove values as needed.
Up to this point no brain work has been involved or typing
numbers... Ps was just doing what it was designed to do... map
original brightness values along with individual R,G,B, values.
The slight brain work necessary for correction, engaged at this
point only becouse you have to decide how to adjust the individual
R,G,B, values placed on the individual curves. If only one value is
out, well... if all values are different or two are out... you will
need to back track and look and mesure a lighter value so you can
judge better the color shifts.
By Control clicking on the value placed on the curve the anchor
piont can be removed.
Once you neutralised the color shift the values placed in the
composit RGB chanel will allow correction of the over all
brightness of the image, or if you know the original brightness
value of the test targets after color adjustments... navigating
through the individual color channels, the keybord command~ will
bring you back to the composit RGB channel, here a mapped
brightness value can be raised or lowered to the known original
value, 20 is the mesured and neutralised value, but the "original"
value was 25, well with ~ you are back in the composite RGB, so
with the up arrow move up the mapped 20 value to 25...
You will have to do these steps ... mesure, place values, correct
in individual RGB channels, with the last step befoe moving to the
next graypatch (~ in composit RGB) adjust the brightness value...
Next...Save the curve adjustment.
Start a new Action set, start recording and open next image, apply
saved curve correction, save and close. Apply this action to a
folder of images needed correction.
Simple as borscht. Please send money!
Best

Tony K
Click to expand...
--

One additional comment, if your capture is relativly accurate, so you do not have mixed lighting set up with tungsten and all kinds of fluorescent tubes here and there, your raw capture is not messed up ... the above mentioned Ps adjustment with curves will correct the color shifts not only with your greyscale values but also will remove the color shift contaminating your original colored objects. You just need to use PS as it was designed to function. and you will get 100% results.
Tony K
 
BW patches on a grayscale are rarely neutral to start with so expecting them to be uniform may not work.

If these images were shot under uniform lighting, a white/gray balance done on the middle patch should be closest but there are no guarantees here.

With a digital camera, a correct white balance on a known neutral target like a Kodak 18% gray card would have been the best bet but there is no real test to check if the camera responds linearly to changes in lightlevels. The various gray steps from dark to light may not be neutral as you are now finding out.

Patches even when included may not even get the same light and a little specularity can change the neutrality.

Unless you use copy lighting in a darkened area with barndoors to prevent reflections off adjacent walls there is little hope that colors will ever be uniform. Even when copying onto special films and color patches and gray scales were included, the grayscale often showed tone differences.

When measuring in Photoshop, make sure the eyedropper is set to 5 pixel x 5 pixels so that image noise is not responsible for color differences.

Bottom line is that you may be too picky to expect perfection where it did not exist.

All being said and done, Photoshop can do what you want but it requires many layer masks with adjustments in curves to get all the patches uniform (or real close) enough. Those layered effects need to be applied to all the other images and that only works if the density of all images is also identical.

My comments here are only musings so that you may understand that there is a lot more to it than what meets the eye.
Rinus of Calgary
 
Ranjan said:
Here is the sample image in sRGB space, klik on link to download a
330 kb file
http://images.fotopic.net/?id=2712474&outx=600&noresize=1&nostamp=1

Thanks for the suggestions I will try the described methods & see
if something works.
--
Ranjan
Professional photographer.
http://www.photosig.com/go/users/view?id=11993
Click to expand...
--

Have looked the test file, your RGB values are out consistently in the Red and the Green channels for the assumed neutrality and brigthness values of the greyscale.
Correction with above technic described by me would take minutes.

The test file was too compressed to atempt, but the mesured caracteristics are uniform. If you have a solid patch ( color) that is a known RGB value in the target you would see the same shift in them as well.
Life is simple with these corrections.
Tony K
 
Member said:
Bottom line is that you may be too picky to expect perfection where
it did not exist.
Click to expand...
I agree, while photography is a science, i find science can get in the way of making great photographs...at least for me. When judging color shifts the best way is in a medium shadow cast on a white card. This should be around the middle gray value that PS works with. Don't go knocking yourself out over the little things when, as everyone has mentioned, there are a lot of variables. Especially the product you will be shooting. I have extensive experience shooting and fabric dyes are notorious for doing strange things to film and now digital. I use to keep different film stocks on hand because Provia or Ektachrome might not be able to accurately render a dye but the other would.
However you might want to check this out :
Member said:
http://www.picto.com/
Click to expand...
they make some plugins that measure charts.
 
Ranjan,

The sample you posted had a lot of JPEG artifacting and it isn't easy to point sample an image like this. However, this is neutrally balanced as near as I could get it with absolute black and pure white on either end of the scale. It was done using a method along the lines of another poster with eyedropper sampling to set reference points for white, black and gray, then using curves on each channel to even out the casts. You really shouldn't have any problem with an image like this unless the original is JPEG'd as bad as this one.
Corrected sample: http://www.vizualgroove.com/digitalimaging/carpet1.htm
Regards,
VG
Ranjan said:
I ran into a critical color correction problem where I found that
PS is not able to do a perfect job.

I shot a color target from profile prism & wanted to create a
correction which can be applied to all the shots of carpets shot in
the same light. The target has a row of netural patches in lower.
PS cannot do all the patches netural by any methods, I tried
levels, varitions, curves, selective color, additional plugins,
finally I found that Edit lab can do it much better correction of
all the patches.

I feel PS does not have perfect answer to this, I may be wrong but
cannot find a method to to the following.
I shoot a series of grey patches from white to black with my studio
flash, the grey patches show unequal RGB numbers, I want to
neturalize all the patches with equal RGB values ie: 10.10.10/
50.50.50. 80.80.80. & so on till 255.255.255.
I cannot find any such method via any tools to do so.
Edit lab did it 90% correctly but not 100%.
Can anyone tell me how to to this in PS7 CS

--
Ranjan
Professional photographer.
http://www.photosig.com/go/users/view?id=11993
Click to expand...
 
SnapJack said:
SnapJack said:
http://www.picto.com/
Click to expand...
they make some plugins that measure charts.
Click to expand...
I indeed checked that out & used icorrect editlab to correct neturals which does the job in seconds much better way than PS, thats why I am left wondering cant we do the same in PS.

My answer is no(since I have failed)bcoz in PS levels there are only three sliders shadows mid tones & highlights. For the sake of comparision lets say that the shot does not contain shadows 0 0 0, or midtone 128 128 128, & no highlight 255 255 255. But the same shot contains many neturals PS will force you to change your black point, mid point etc, where as Edit lab will do the same job without changing it.

I dont want to change my black point(which PS does)I just want to correct my neturals only.

Here is a better explanation, PS has 3 zones for correction where as Editlab shows 5 of them but uses (in real) 10 zones to correct the neturals.

http://www.picto.com/UserGuides/iCorrectEditLab40/ColorBalToolA.html
--
Ranjan
Professional photographer.
http://www.photosig.com/go/users/view?id=11993
 
VG said:
Ranjan,
The sample you posted had a lot of JPEG artifacting and it isn't
easy to point sample an image like this. However, this is neutrally
balanced as near as I could get it with absolute black and pure
white on either end of the scale.
Click to expand...
Sure PS did a great job but it changed the density of the neturals, I only want to balance RGB values not change the density, since that will be done later at CMYK stage keeping account for the dot gain.
VG said:
It was done using a method along
the lines of another poster with eyedropper sampling to set
reference points for white, black and gray, then using curves on
each channel to even out the casts.
Click to expand...
if the image does have neturals, but no real white point, mid point & black, then what is the way out to neturalize the RGB values. Your results is far to contrasty since PS forced you to make the black as 0 0 0 where as, it should remain as it is since the exposure & WB were taken care seprately & are spot on. My grey card shot reads value 128 128 128.taken in the same conditions.
--
Ranjan
Professional photographer.
http://www.photosig.com/go/users/view?id=11993
 
Ranjan

PS didn't force me to do anything. I believe you are missing the whole point of white balancing. I set the black patch to full black and the white to full white for a comparison.

Camera WB is not based on a middle gray value. Also, different cameras will mix the RGB values a little differently to achieve the same colors. If you are trying to match exact RGB values to CMYK values, you still have to establish a white point.

You didn't mention whether you are shooting RAW or JPEG. JPEG can have different camera settings that will affect the color composition of the image. RAW is much easier to WB with.

You said my sample was much too contrasty and I agree. You can simply raise your black point using the method I used. The sample you posted is very washed out and this makes me think your monitor calibration, especially the gamma point, may be off. I use a Lacie Electron IV Blue hardware calibrated monitor and my sample was a bit dark and contrasty. However, not knowing how you exposed for this image, it looks like center weighted as the card has a lot of reflective white, and this can throw off the contrast and WB as well.
Regards,
VG
Ranjan said:
VG said:
Ranjan,
The sample you posted had a lot of JPEG artifacting and it isn't
easy to point sample an image like this. However, this is neutrally
balanced as near as I could get it with absolute black and pure
white on either end of the scale.
Click to expand...
Sure PS did a great job but it changed the density of the neturals,
I only want to balance RGB values not change the density, since
that will be done later at CMYK stage keeping account for the dot
gain.
Member said:
It was done using a method along
the lines of another poster with eyedropper sampling to set
reference points for white, black and gray, then using curves on
each channel to even out the casts.
Click to expand...
if the image does have neturals, but no real white point, mid point
& black, then what is the way out to neturalize the RGB values.
Your results is far to contrasty since PS forced you to make the
black as 0 0 0 where as, it should remain as it is since the
exposure & WB were taken care seprately & are spot on. My grey card
shot reads value 128 128 128.taken in the same conditions.
--
Ranjan
Professional photographer.
http://www.photosig.com/go/users/view?id=11993
Click to expand...
 
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