Expert: LizaL - 5/28/2006

Question
Dear Lizel,
   this question may be somewhat long-winded but please bear with me.  Unfortunately I do not understand that concept of the color wheel.  Basically if I have a red cast in a photo I have scanned into Photoshop or a blue cast I believe the correct tool to use is the selective color tool.  However I do not understand the concept of how to use selective color tool.  I do understand it has something to do with understanding  the concept of the color wheel.  Let me try to make the next sentence more clear if I have a slight blue cast to a photo that I have scanned into Photoshop using the selective color tool what would be steps No. 1 3 and 4.  I would be most appreciative for your expert help in this matter.  Needless to say in the past your advice and technical expertise has been in excess of 100 percent.  Just to refresher memory, I am using a canon scanner at 4000 DPI a gateway computer Photoshop No. 7 and a Epson printer.

On a personal note I hope this holiday find you and your family in good health with many years of the same  I remain respectively yours Stewart Arno

Answer
Hi Stewart!

Sorry you're having some confusion, but it's still good to hear from you! Hope all is well.

Color casts on photos can be a pain, but they're usually pretty easy to fix. I've assembled some links for you that you might look at when you get a chance that discuss color theory. I'll post those links at the end of this message.

I never thought about the color wheel playing a part in using the Selective Color command, but I can understand what you're saying. Selective Color uses CMYK color (process color) to perform its corrections -- and CMYK is a color model used for printing. So I can see where you might associate the color wheel with the Selective Color command.

I can also see why you'd associate the color wheel with Selective Color when you think about colors being comprised of different components. For instance, you can have a shade of blue that is technically made up of not only blue, but red, and possibly green. In other words, colors aren't always *pure*.

Anyway, the good news is, even though you might be a bit hazy about the color wheel, it's not that necessary to be really familiar with its workings in order to use Selective Color. I'll explain:

1. As I mentioned, Selective Color operates using CMYK, but you can use it on RGB images. It's based on a table that shows the amount of each process ink (Cyan, Magenta, Yellow, and Black) used to create each primary color (Red, Green and Blue).

By increasing and decreasing the amount of a process ink in relation to the other process inks that make up the colors of a picture, you can modify the amount of a process color in a primary color. For example, you can use the Selective Color command to decrease the red in the magenta component of an image while leaving the red in the blue component unaltered.

Take a look at this example.

http://little-works.com/all_experts/greencast.mov

What you see here is an image with an obvious green cast. Using Selective Color, I chose the Greens color tab and decreased the Cyan component of the picture, pretty drastically. That made the yellow more prominent, so I decreased it, as well. And doing this also altered the magenta, which I tweaked some, too.

Doing all this still leaves the guy's face in a shadow, but that can be fixed too -- more on that in a second.


2. You can also use Levels to decrease casts in a photo. Using the same photo, I used Levels to tweak out the obvious green. Look at this:

http://little-works.com/all_experts/levels1.mov

What I did was select the left-most eyedropper tool, which measures shadows in a picture, and I clicked on the picture, in a place that looked like it might measure very dark. Then I clicked on the right-most eyedropper, the one used to measure highlights, and clicked on what I perceived as two very light areas of the photo. And almost instantaneously, the cast is removed.

However -- this is a REALLY down-and-dirty way of fixing a cast! It alters the histogram, as you can see, very quickly. And you have to be careful not to get blown-out areas, like I started to get when I clicked in the far left light part, in the window. But if you're careful, you can use this to quickly remove a cast.

Basically what happens when you do this is, by clicking on the darkest part of the photo, then the lightest, you're asking Photoshop to sort of gauge the middle ground, and set the photo to that middle point, which removes the cast.


3. To remove the shadow from the guy's face, as mentioned above, I'd use a very simple adjustment with Curves, like this:

http://little-works.com/all_experts/curves1.mov

Again, this is a pretty down-and-dirty way of using Curves, but it removes the shadow. I visually estimated where the shadowed area occurs in the photo (the guy's face), and placed a point along the Curves histogram at that point, and dragged slightly up and to the right, which increases highlight. It's almost like putting a spotlight on the guy's face.


4. The image I used came from Katrin Eismann's Web site. She's an expert on photo restoration and retouching, and I hold her expertise in high regard. Here's the link to that site, which contains some downloadable PDFs, practice images like the one I used, and good information on color correction:
http://www.digitalretouch.org/

Over on the left frame are the links for sample chapters and tutorials, etc.



5. This tutorial is for removing a cast with Thresholds, and also Curves. It basically expands on the down-and-dirty ways I mentioned above! It looks like a good tutorial, to me.

http://www.worth1000.com/tutorial.asp?sid=161031&page=1


6. About the color wheel... basically, it's a color model that groups colors together so that they have a chromatic relationship. There are a lot of color models, but the wheel is one of the most familiar. It was first discovered and researched by Sir Isaac Newton. In brief, it grows from the concept of primary colors, to their chromatic "relatives" on the wheel, which would be the secondary colors. Then the next tier would the tertiary colors, which expand chromatically from the secondary colors.

Some links to color theory sites:

-- This is a good introduction to the color wheel, itself, and it goes on to explain the tiers of the wheel as you move past the basic colors:
http://www.tigercolor.com/color-lab/color-theory/color-wheel.htm

-- This site's also not too bad for explaining basic color theory:
http://www.worqx.com/color/color_wheel.htm


Well, as always, I hope this helps! Thanks for the holiday wishes, and the same to you and your family!

Lisa


P.S. That wasn't a long-winded question at all, but I'm sorry for the long-winded answer!!