Image Help - - color corection by the numbers

dawghair · #1 07-17-2005, 09:18 PM

999999999999999

Duv · #2 07-17-2005, 09:51 PM

Welcome aboard!! I would recommend as a starting point getting some good books on the subject. Two books I would suggest is Katrin Eismann's Photoshop Restoration & Retouching and Michael Kieran's Photoshop Color Correction. They're the real pros at explaining color correction which can be very simple or extremely difficult. Both books come with a CD of images that you'll find very helpful in working thru the color correction problems.

Cheers
Dave

GaryRP · #3 07-17-2005, 10:04 PM

Agree with Dave ..

Katrin's book is almost a "mandatory" buy for anyone doing photo restoration.

v.bampton · #4 07-18-2005, 03:04 AM

In the meantime, a couple of articles to get you going...

http://www.adobeevangelists.com/pdfs...tByNumbers.pdf

http://www.ledet.com/margulis/PP7_Ch02_ByTheNumbers.pdf

If you're working in CMYK, Dan Margulis has written a great book specifically on color corrention, although he does go into an amazing amount of detail, so prepare to have your mind blown away! The 2nd link is a copy of one of the chapters out of his book.

Hope you get on ok.

Victoria

PatrickB · #5 07-18-2005, 01:50 PM

Hello and welcome to RP!

The easiest way to color correct an image is by using the curves neutral picker: Go to image/adjustment/curves. Click the neutral color picker between black and white color picker in the lower right of the window. Locate a real neutral spot in the image, gray, dark white or something and click. This automatically adjusts the colors.

Another way is to use color balance or the curves tool with the three channels, but that's a little too pro I guess?

http://www.adobeevangelists.com/pdfs...tByNumbers.pdf

Might help as well!

Patrick

Cameraken · #6 07-18-2005, 07:50 PM

Dawghair
Welcome to RetouchPro

What program are you using?
Are you working in RGB or CMYK?
If all your pictures are similar then post one here and someone will help.

The second link that V.bampton posted (above) is probably the best tutorial on the WWW.

I have a couple of related questions.

Is there anything that you can’t do using curves in RGB alone?
Is there any advantage to converting to LAB etc?

I understand I can adjust brightness/contrast/colour etc.
But What about something like copying the red channel to the blue channel?
Is that possible using only curves? Or am I doing that already in a different way?

Ken

Flora · #7 07-19-2005, 01:17 AM

Hi dawghair,

Welcome to RP!

This is something I really can't help you with ....

.... but I know you'll get a lot of help by Members who are really very good at it ...

I'm merging your two Threads since they are about the same topic ...

v.bampton · #8 07-19-2005, 02:41 AM

Quote:

Originally Posted by Cameraken

Dawghair
I have a couple of related questions.

Is there anything that you can’t do using curves in RGB alone?
Is there any advantage to converting to LAB etc?

I understand I can adjust brightness/contrast/colour etc.
But What about something like copying the red channel to the blue channel?
Is that possible using only curves? Or am I doing that already in a different way?

Ken

Hi Ken

There are LOADS of things you can't do in RGB curves alone. In a real world situation though, processing loads of pictures, sticking with RGB will do you nicely. LAB is great in that you can affect the luminosity values without affecting the colour at at all, but unless you're working on a nightmare picture, it's rarely needed.

Copying the red channel to the blue channel... you mean literally replace the blue channel with red? I can't think of a way of doing that with curves. A direct replacement - how about you turn off the other channels, so you can only see red - ctrl+A to select all, ctrl+C to copy, turn the red channel off, and the blue channel back on, and ctrl+V to paste - and bingo, you now have a replaced channel. That changes the colours though, obviously - is that what you had in mind? What are you planning on accomplishing?

If you can post a couple of examples Ken, we might be a bit more help!

Victoria

Cameraken · #9 07-19-2005, 06:54 AM

Patrick

“Locate a real neutral spot in the image”

You make it sound easy. I’m still learning and maybe this gets easy with practice. One way I have found to ‘Find’ a neutral is to set the foreground colour to mid grey then
Select > color range > sampled colors
By lowering the fuzziness the mid greys can be found. (if there is one)

Victoria.
Thank you for your response. I suppose my question should have been
Is there anything you can’t do with curves that is in the image > adjustments section

I was thinking of very damaged pictures. The way you mentioned of replacing a channel is the way I do it now (or use the channel mixer). I was thinking that because the channel mixer is in the image > adjustments section there must be a way to do this with curves.
I think I’m beginning to answer my own question. Replacing a channel is an attempt to improve the luminosity of that colour.

Ken

v.bampton · #10 07-19-2005, 10:53 AM

Quote:

Originally Posted by Cameraken

I suppose my question should have been
Is there anything you can’t do with curves that is in the image > adjustments section

Curves are powerful, but the other tools are there for a reason - they can't all do exactly the same job. There is some crossover between tools - there's more than one way to accomplish almost everything - but just using curves won't cover every scenario.

Off the top of my head, I can't think of a way of increasing the saturation a great deal just using RGB curves, whereas with Hue/Saturation that would be easy. Selective colour is another tool that is almost impossible to replicate using curves alone. Does that make sense?

Quote:

Originally Posted by Cameraken

I was thinking of very damaged pictures. The way you mentioned of replacing a channel is the way I do it now (or use the channel mixer). I was thinking that because the channel mixer is in the image > adjustments section there must be a way to do this with curves.
I think I’m beginning to answer my own question. Replacing a channel is an attempt to improve the luminosity of that colour.

Sounds like you've got the idea Ken. It is one of those situations that there are loads of different ways of working, and the way you choose will depend entirely on the specific picture.

Cameraken · #11 07-19-2005, 11:44 AM

Victoria.
Thank you for your reply.

One reason for my questions is that I downloaded Curvemeister demo from
http://www.curvemeister.com/
It watermarks the results but it is fully functional and I liked the idea of being able to pin skin tones, hair etc all in one tool.

But I suppose a tool like this would be more useful to a learner, and someone more advanced would not really need these extra curves features. Like you have just explained it still cannot do everything.

Ken

PatrickB · #12 07-19-2005, 02:38 PM

Hi Ken,

sorry for being so unprecise. What I meant by saying "find a neutral spot", I'd post an example:

Imagine you have a photo with a sever blue cast, anything on the picture is blue. Then just locate a spot on your picture that you know right from your mind that it's supposed to be gray, white or something in between, without any color. This is a neutral!

Does that lighten things up?

Cameraken · #13 07-20-2005, 04:11 PM

Patrick.
Thank you for your reply. I think I’m beginning to understand.

I am at the moment trying to work through this workflow
http://www.luminous-landscape.com/tu...orkflow1.shtml

It seems pretty good and I think Dawghair may be interested in reading it.

I just wondered what you all think of a workflow like this. Is there anything missing?

Sorry if this is off topic a bit

Ken

PatrickB · #14 07-20-2005, 04:37 PM

I had a quick view of this workflow, but I guess it's worth looking a little bit closer

Two things popped into my eye:

- The author says it's needed (somewhere in the middle) to convert to LAB. I see no use in converting an image and losing valuable information occuring when converting 8-bit RGB to LAB (oh my god what a sentence)

- I also discourage using the Levels to "stretch" a histogram. If an image really has no white or black spots anywhere, why should I create them and ruin the midtones?

*goingonreading*

v.bampton · #15 07-21-2005, 01:32 AM

Quote:

Originally Posted by PatrickB

- The author says it's needed (somewhere in the middle) to convert to LAB. I see no use in converting an image and losing valuable information occuring when converting 8-bit RGB to LAB (oh my god what a sentence)

I'd always understood, Patrick, that converting to and from LAB was lossless. Not quite sure where I read that, and I haven't got time to look right now as I'm meant to be getting ready for work! Any thoughts though?

Victoria