Color Correction Advice

The original sRGB has never used a gamma curve. It uses a TRC; they are not the same. A TRC may follow the gamma formula or may not. A gamma curve always does.

http://digitaldog.net/files/LinearityandGamma.pdf

Only AdobeRGB uses a true 2.2 gamma curve, but I suspect sRGB was what the authors of that old article had in mind with their table of gamma 2.2 values

Also, Adobe RGB (1998) among other Working Spaces use a true 2.2 Gamma Curve. It isn't unique in that respect. So only? No sir.

Oh, when discussing sRGB, it sometimes helps to define which sRGB:

sRGB profile comparison

See Table A2.

Rodeo Joe and others are right in questioning whether you need the kind of precision you seem to be asking for, for your purposes.

 

His Q&D tonal adjustment can get you close enough for a starting point, and then you can play with adding 'filters' in a reasonably complex image manipulation program to get something that "looks' right to that mark 1 eyeball

They calibration target is in every image so I thought I would try to use it. If there were all photographed at the same time / conditions, I can apply the correction for one target to all. so it is not that difficult. This would eliminate the ambient effects so I can focus on color matching to high quality text books Images.

Also what is "Q&D"

If I want to mathematically match the colors/exposure of a target image (image to be corrected) to a reference image, could I do this by calculating the difference or ratio of the two images in PS, and scale the target image to match the reference image. I would have to make sure they are physically scaled to the same size /alignment. Would it be better to do each color channel independently in RGB of CMYK?

Method 1 - Differential Error

Layer 1 - Reference Image

Layer 2 - Target Image

Layer 3 = (Target - Reference) / Reference

Layer 4 = Target / (layer 3 +1)

Method 2 - Ratio

Layer 1 - Reference Image

Layer 2 - Target Image

Layer 3 = Target / Reference

Layer 4 = Layer 2 / Layer 3

If this method works, then I could do this in Matlab, and have all the 100 images processed in a minute or so. But I suspect it is not that easy.

BTW, I just realized what Q&D means

If I want to mathematically match the colors/exposure of a target image (image to be corrected) to a reference image, could I do this by calculating the difference or ratio of the two images in PS, and scale the target image to match the reference image. I would have to make sure they are physically scaled to the same size /alignment. Would it be better to do each color channel independently in RGB of CMYK?

 

Method 1 - Differential Error

Layer 1 - Reference Image

Layer 2 - Target Image

Layer 3 = (Target - Reference) / Reference

Layer 4 = Target / (layer 3 +1)

 

Method 2 - Ratio

Layer 1 - Reference Image

Layer 2 - Target Image

Layer 3 = Target / Reference

Layer 4 = Layer 2 / Layer 3

 

If this method works, then I could do this in Matlab, and have all the 100 images processed in a minute or so. But I suspect it is not that easy.

BTW, I just realized what Q&D means

Don't take this the wrong way but...

“There seems to be some perverse human characteristic that likes to make easy things difficult.” -Warren Buffett

You could however, fix one image visually, doing this all on an Adjustment layer, then drag and drop it on all the others.

Or create a preset of the fix visually and copy/paste them to all others in say Lightroom/ACR.

Don't take this the wrong way but...

“There seems to be some perverse human characteristic that likes to make easy things difficult.” -Warren Buffett

You could however, fix one image visually, doing this all on an Adjustment layer, then drag and drop it on all the others.

Or create a preset of the fix visually and copy/paste them to all others in say Lightroom/ACR.

Sorry, I have not explained my goals in enough deals. I started off posting a color correction question based on a target.

There are two levels of adjustment I need to do

1. Color correction for ambient conditions (this is not that difficult)

2. Color/Exposure restoration of the target print to match a published museum quality version

Each of the 100 target images have been collected from different sources, storage conditions, different print dates etc. over the past 150 years. The target Images need to be individually corrected to match the higher quality version.

Sure, I can do this by eye for the 100 prints. 25-50hrs of work. Just curious of there are some computational solutions that are less subjective.

"Q&D" - Qick 'n' Dirty. Which I admit my quick restoration of the paper base to near-white was.

Unless you have access to 16 bit, or at least 12 bit images, then doing the adjustments in two stages isn't a good idea. And what good does it do you to get the base paper to its currently 'correct' shade of yellow or dirty brown? When you'll only have to reduce the red/green channels, or boost the blue, or both, to get close to the unfaded and un-aged look the artist created.

If you want automation: Try cropping the images to exclude everything except the drawings and simply hit 'Autocolor' in Photoshop.