Color Replacement in Photoshop

This lesson continues the cycle dedicated to the basics of working in the Lab color space. I give here only the main points of the work, not dwelling on the intricacies and particulars. Those who want to learn more about working at the Lab can purchase Dan Margulis’s book “Photoshop Lab Color. The Canyon Mystery and Other Adventures in the Most Powerful Color Space”

Many were faced with the desire or the need to change the color of an object in a photo, and I would like to do it as realistically and quickly as possible. It would seem that the tasks are contradictory, especially if you have already tried to do something like this, spending a lot of time creating and fine-tuning masks, “dancing with a tambourine” above the keyboard and monitor and experimenting with various fills, gradients, channels and corrective layers.

Lab offers another solution: quite simple, fast and elegant. If after completing all the steps you need to work with a mask, then it will be rather finishing strokes, but not a tiresome drawing. The technique in brief is as follows:

Step 1. We translate the image into Lab mode. If you read previous lessons on this topic, for example, “Correction in the Lab”, then you know how to do it.

Step 2. We determine the color and how it can be obtained. Suppose that a client asked him to repaint his car in the photo in a strictly specific color, for example, Pantone Black 6C. Adobe Photoshop has the so-called Pantone color libraries (this is an international standard for color). Access to them is available through the palette. Colour (Color), either through the toolbar, by double clicking on the primary color icon,

then press the button Flower library

Then we find the color we need (they are numbered in ascending order from top to bottom) and remember the channel values ​​for Lab. In this case, it is L = 9, a = -3, b = -7.

Step 3. We find on the image of the car the area that best describes its color. It should not be reflections, glare, it should not be in deep shade or in bright light. In this case, it will be a point slightly below the right headlamp. Put in this place a reference point.

Step 4. Create an adjustment layer Curves (Curves). This, too, should not cause you difficulties. If it does, see the lessons, where it is shown how this is done.
Now, by changing the curves, we select the channel values ​​for our point, referring to the Info palette (Info).
Attention! It is very important that the channel curves a and b passed through the center point! When you change the shape of the channel curve Brightness (Lighness) it is important to take into account its slope, since its change will lead to a change in the brightness contrast of the object. Sometimes it is needed, sometimes not.

Here is what we got at this stage.

Now we need to return the color to the rest of the objects.

Step 5 Double-click, to the right of the layer name, call the dialog box Layer style Overlay options. Now, using the engines of each channel, we will separate the car from the rest of the objects. Learn how to work with the Blending options feature.

Step 6. After a little conjuring with regulators, we get the desired result.

I do not explain exactly how to use the controls, each image will have its own individual settings. Experience is gained through practice.
I spent about 5 minutes on changing the color of the car in this way. Try a different way and compare the effectiveness.

I want to immediately warn for some images this method will not work. In particular, for those where you need to greatly change the numerical value of the curves of the channels a and b (for example, from 1 to 50). In such cases, replacing one channel with a copy of another is used, sometimes with a change in the blending mode (External Channel and Calculations commands).

I wish you all creative inspiration and success!
Author: Evgeny Kartashov

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