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In today's quick tip, new Cgtuts+ author Dimitar Katerov shows us how to alter lighting information by Black & White Adjustment in Photoshop. This allows you to change the appearance of a texture or a 3D render by easily tweaking the light to a particular color range in your image. This is an extremely useful technique when working with bump and specular maps. Let's take a look!
Black & White Adjustment can be used directly for making Bump, Specular or Displacement maps. It is very easy to use and most of the time you don't need any complex masking for achieving nice results. If you just make a desaturated copy of your image for Displacement or Bump textures for example, you could get the wrong height information because some of the creases in the actual subject may be painted in a brighter color, and as a result may be generated higher on your 3D model. If you only Invert such an image, there may be incorrect data in other areas as well, so the best way to do this is to use Image>Adjustments>Black & White (Alt+Shift+Ctrl+B) where you have independent control over six major color groups and you can easily tweak the final look of your map. In this tutorial I will show you how to use the Black & Light Adjustment Layer to change the appearance of an image and applying it to textures.
Open the image that you want to manipulate. Duplicate the Background layer by dragging it to the New Layer icon on the bottom of the Layers panel or by going to Layers>New>Layer via Copy (Ctrl+J).
Now that we have two layers, we will use the top one to transfer lighting information to the Background layer. To achieve this, change the blending mode of our layer copy to Luminosity. This way it only transfers the light value information to the Background layer.
Instead of directly applying Image>Adjustments>Black & White, it's better to use an Adjustment Layer so you can change the look again and again if you want to.
Click the adjustment icon in the Layers panel and choose Black & White.
Hold the "Alt" button and when you hover over the line between the Black & White and the "background copy" layer, the cursor changes to indicate you will create a clipping mask. Click once, now the Adjustment Layer is only affecting the "background copy".
Now change the values in the Adjustments Panel as you like. You can see the final result as you move the sliders. To see only the Adjustment applied to the copy, you can hide the Background Layer.
You can apply this method to any image. If you want to use it for making Bump, Displacement, Specular and other grayscale textures, you must directly apply the Adjustment to Background layer, because you don't need the color data that the above method saves.