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Posted on 12/03/06 8:22:14 PM |
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Bob
Expert Expressionist Posts: 130 Reply  |
Match colors using Levels
This tutorial describes how to match colors using the Levels adjustment tool. This will be particularly useful for users of Photoshop Elements which does not provide a native Curves adjustment tool. Matching colors using Levels can produce results comparable to those obtained using the Curves adjustment tool with a standard “three point” (i.e. two endpoints and a midpoint) curve. We will be using the photo from “How to Cheat in Photoshop” that was used to illustrate how to match colors using the Curves adjustment tool. If you have the book, you can compare the two techniques and practice using the same photo. Here is the original photo. 
Begin by select the layer containing the hand and bring up the levels dialog. You can directly work on the layer by typing command+L (Mac) or ctrl+L (PC). Alternately, you can use a levels adjustment layer. From the menu, select Layer>New Adjustment Layer>Levels... – be sure to check the box that says “Group with Previous Layer” to ensure that only the layer containing the hand will be affected. Pressing option (Mac) or alt (PC) while selecting the Levels adjustment layer from the Layers Palette will also bring up this dialog box. Using an adjustment layer will allow you to make a non-destructive correction which you can come back to later and modify should you decide it needs to be tweaked. We can now match the colors by following these steps. Step 1: Determine which color should be corrected first by choosing the color that needs the greatest change. Remember that you can only change the levels of the three primary colors, Red, Green, and Blue. Reducing a primary color will be similar to adding the complementary color (Cyan, Magenta, and Yellow). If you were to actually add the complementary color instead of reducing the primary you would darken the image – you generally don't want to do this. In this photo, the hand appears to be much bluer than the face so select the Blue channel using the pop-up menu. Click on the gray triangle slider and drag it to the right to remove the blue cast from the mid-tones. This will make the hand appear yellower, which is what we want. Since the slider mainly affects mid-tones, there may be a residual cast in the highlights or shadows. We will take care of that in the next step. 
Step 2: The blue cast was removed from the mid-tones but there is still a noticeable trace of blue in the highlights. We can correct this by adjusting the output levels. Click on the white triangle in the Output Levels section at the bottom of the dialog and drag it to the left to limit the brightest part of the blue channel and remove the highlight cast. There is no blue cast in the shadows. Had there been one, we could have clipped the shadows by dragging the black input level slider to the right slightly. 
Step 3: We've finished with the Blue and the hand still does not match the face. It appears to have a slight greenish cast. Reducing Green will make the hand more Magenta. But, when we compare the hand to the face, we can see that it needs to be more Red not more Magenta. That means it's actually more of a Cyan cast and we need To increase the Red. Switch to the Red channel and drag the gray triangle slider to the left. 
Step 4: The color is now fine, we don't need to make any additional color adjustments. Now it's time to address the tonality. Examining the photo, we can see that the contrast of the hand is too high to match the face. In particular, the shadow on the hand is much too dark. To reduce the shadow on the hand, switch to the RGB channel (which affects overall contrast and brightness). Then, click on the black triangle in the Output Levels section at the bottom of the dialog and drag it to the right to limit the depth of the darkness and thus lighten the shadows. 
Step 5: Finally, reducing the shadows lowered the contrast of the hand somewhat. It looks flat compared to the face. We need to increase the contrast a bit. While still on the RGB channel, click on the white triangle in the Input Levels section (NOT the one in the Output Levels section) and drag it to the left. This reduces the tonal range and increases the contrast. 
We're done. Click ok to accept the Levels adjustment. How Levels corresponds to Curves The Levels adjustment and the Curves adjustment perform similar operations. In fact, you can consider the Levels adjustment to be an alternate interface to adjust a curve with three points – the two end points and a middle point. There is a direct correspondence between the sliders in the Levels adjustment and the points in the Curves adjustment. 
As shown above, the Levels adjustment has five sliders, two in the Output Levels area, and three in the Input Levels area directly below the histogram. Sliders A and B control the position of the lower left curve end point. Slider A moves the point horizontally while B moves it vertically. Similarly, sliders C and D control the position of the upper right end point. The gamma slider, control E, adjusts the vertical position of the middle curve point. Moving E left causes the point to move up while moving E to the right causes the point to move down. |
Posted on 13/03/06 3:18:14 PM |
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Steve Caplin
Administrator Posts: 7009 Reply  |
Re: Match colors using Levels
Excellent, Bob! That's really clear. Many thanks! |
Posted on 13/03/06 4:12:13 PM |
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Lexus
Persistent Pixellator Posts: 623 Reply  |
Re: Match colors using Levels
Yer, Great One Bob, Thanks. I'll Try It Out Later! Wow, I Hope This Tutorial Section Gets Full Up!! Need To Learn Some More Stuff! _________________ 3TV Visit http://www.3television.co.uk and watch. You will love it! |
Posted on 14/03/06 03:41:17 AM |
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Pierre
Constructional Confabulator Posts: 637 Reply  |
Re: Match colors using Levels
I've using levels for a little while now and somehow had a visual understanding of how they work (in my brain, don't ask me to explain). But I had a tough time getting a similar understandign of the Curves. Well now I don't need to try anymore! I tried the level adjustment and got it the first time around! Great tutorial! More, more! Pierre _________________ |
Posted on 14/03/06 10:11:45 AM |
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Bob
Expert Expressionist Posts: 130 Reply |
Re: Match colors using Levels
Thanks for the feedback, it's much appreciated. I was hoping it would be useful. 
I wrote this tutorial to test out the new tutorial section and "prime the pump", so to speak. I hope others will contribute also. I wouldn't mind working up more tutorials. If you would like to see something specific, please place a post in the tutorial requests section. |