Help a Photoshop novice with auto color correction!
March 19, 2010 12:21 PM   Subscribe

Is there an action / tool / simple, built-in feature in Photoshop CS4 that will auto-correct color levels based on what I choose as a neutral color (like Picnik does)? Image>Auto-Color isn't cutting it.

Picnik will do a really nice re-color of a photo based on what you select as a 'neutral' color. You select a portion of the photo that should be white or grey and the software adjusts the levels to make it so, therefore correcting the whole photo. I would like to do this in Photoshop.

The only functions I've found in Photoshop are:

Image>Auto Color
Doesn't prompt for a neutral color picker and is therefore not working for me)

Image>Adjustments>Color Balance
Works okay for me, but I'm not sure my vision is refined enough to tell when something has too much red vs too much yellow.

...or a multi-step, advanced technique that is probably above my abilities (for example)

Is there an Action / Add-on / etc that would achieve this with only a few clicks?
posted by jeffrygardner to Technology (10 answers total) 4 users marked this as a favorite
Image > Adjustments > Levels ?
posted by amethysts at 12:27 PM on March 19, 2010 [1 favorite]

Best answer: You can set the white, black, and gray point in Levels.
posted by zsazsa at 12:38 PM on March 19, 2010 [1 favorite]

Best answer: Yes, what you want is the Levels tool. Once you've got it open (Image > Adjustements > Levels), select the gray eyedropper and click on a gray area of the photo to set a gray (neutral) color point. The white eyedropper sets the highlights, and the black eyedropper sets the shadows. To make things even more adjustable, I usually use Levels as an adjustment layer (Layers > New Adjustment Layer > Levels) so I can adjust the opacity of the changes as well.

Because the gray area / neutral color will be different in every photo, I don't know of a way to do this as an automatic action.
posted by geeky at 12:40 PM on March 19, 2010

I know that when I open my camera RAW files in Bridge / Photoshop it summons the intermediary Adobe Camera Raw application (mini-application? in-betweenlication?) and that does indeed have a white balance dropper tool. I'm assuming if you have CS4 then you have Adobe Camera Raw, but without knowing your OS and so forth I can't tell you what spells to use to summon it.
posted by komara at 12:44 PM on March 19, 2010 [1 favorite]

Response by poster: Thanks, folks! The tutorial from zsazsa was perfect and I like geeky's suggestion to create the adjustment layer first.

Thanks again!
posted by jeffrygardner at 12:45 PM on March 19, 2010

Which is not to say that what geeky laid out is not a better option overall. I'm just letting you know where in my process I usually interact with it.
posted by komara at 12:45 PM on March 19, 2010 [1 favorite]

Response by poster: And, on preview, thanks to komara, too.
posted by jeffrygardner at 12:46 PM on March 19, 2010

I use the same process, komara, but I wasn't sure if the OP was using RAW or not. Also, I vote for "in-betweenlication" :)
posted by geeky at 12:59 PM on March 19, 2010

I prefer to do this with Curves. It's a bunch of steps, but it only takes about 30 seconds to perform once you've done them a few times.

1) Make sure the Info panel (Window > Info) is onscreen.

2) add a Curves adjustment via Image > Adjustment > Curves (or, better yet, a Curves Adjustment Layer).


4) Switch to the Red channel by clicking Option+3.

5) Command+Click the pixel. (Hold down the Command Key and click the mouse, which is still hovering over the pixel). This will place a point (a dot) on the curve, capturing the Red-color-value of that pixel inside the Curves tool.

6) Switch to the Green channel by clicking Option+4. Command+Click.

7) Switch to the Blue channel by clicking Option+5. Command+Click.

NOTE: once you've done this a couple of times, steps 4-6 become really easy and fast: Option+3, Command+Click; Option+4, Command+Click; Option+5, Command+Click. Done!

I am using Photoshop CS4. In earlier versions, those Option shortcuts used 1,2 and 3 instead of 3, 4 and 5. So check your version. Also, if you're on a PC, of course you'll use different modifier keys -- I'm pretty sure you'll use ALT instead of Option and Control instead of Command.

8) look at the RGB values in the info panel. If it's a neutral color (a gray), they should all be the same -- or really close. In an example photo I just used, they were 126r, 97g and 127b. The green is way off!

9) remember or write down the three numbers. YOU CAN NOW MOVE THE MOUSE.

10) calculate the average of those values. I am bad at math, so I use my computer's calculator: 125 + 97 + 127 = 350. Divided by 3 = 116. (Note: in case you're shaky on averages, the average is always all the numbers added up and then divided by however many number their are. Since there will always be three numbers (red, green and blue), you'll always be dividing their sum by three.)

11) In the Curves interface, switch to the Red Channel. You can do this using the keyboard shortcut (see above) or by using the dropdown menu at the top of the UI.

12) In the Output field, type in the average number you calculated. I typed in 116 (see step 10).

13) Switch to the green channel and type in the same number in its Output field.

14) Do the same thing for the blue channel.

15) Click OK in the Curves UI.

You have now changed that pixel from, say, 126r, 97g, 127b to 116r, 116g, 116b, which is a neutral color, found by averaging out the three original colors. Curves does the rest of the work. Because it's "curves," it brings the rest of the pixels in the image along for the ride, which is exactly what you want.

Note: you will get odd results if the pixel you chose wasn't really neutral in the original location -- e.g. if you think it's a gray wall but it's actually yellow. You may be "correcting" a yellow cast that's actually not a problem. Still, you will get the effect that you (supposedly) want. That color will be neutralized and the other pixels will be shifted accordingly.

Sorry this is so many steps. But please note that I belabored it to make it as clear as possible. It really, really does just take half-a-minute or so once you get the hang of it.
posted by grumblebee at 1:03 PM on March 19, 2010

If it's a JPEG or camera raw file, you can also do File > Open, select the file, and then change the "Format:" popup at the bottom to "Camera Raw".

In the raw dialog, you can either set White Balance to "Auto", or select the third icon (starting at the left), or press "I" (it's the "White Balance Tool") above the image, and then use the eyedropper to select a neutral tone within the image.

When you click "Open Image" at the bottom of the dialog, the document will open in Photoshop.
posted by DaveP at 5:30 PM on March 19, 2010

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