Lesson 7: Subtle color: color casts and overlays.

With photos you want to convey messages to people that perceive, judge and interpret and color is a consistent tool to express and refine your creativity. In general the term color cast suggests a predominant "color taste or tint" on a continous tone image. Sometimes undesirable, sometimes desirable, sometimes you want to manipulate it, sometimes you may want to create it.

Theoretically usual problems with color casts are better handled when shooting RAW. In this school we will not dive in the RAW ocean. A photographer will normally want to manipulate color casts and this concept takes its share in a typical photo editing workflow, regardless if you use RAW or not.

After the previous lesson, you should have a fair knowledge about how color is analyzed. Now we proceed to an approach to control color by manually affecting the white balance. Of course these tricks apply to color photography, and every color photograph may theoretically pass this way for a controlled color adjustment.

Getting rid of a color cast

There are cases when you simply want to get rid of a color cast. Your photo seems "redish" or "bluish" or "yellowish" or some other "-ish", something like looking through a color glass. You just want to correct that.

Doing the opposite: adding a color cast

Hey, i guess you have now an idea of how to do it, right? Just do the same thing, select a color etc., but only do not invert the color of the overlay layer!

Editing the color cast

Try this: You can check a color cast "on the fly" by calling the Hue-Saturation Tool on the adjustment layer and with the "Preview" option.

Copying a color cast

Consider the real world scenario. You have shot some photos in the same session with the same light conditions, and you want all of them to have the same white balance -or color tint. Your best bet typically should be to have a shot of a grey card, so that to pick the right adjustment color. If you do not have a grey card, you can make a shot of a surface that you know that it is white, let us say a white wall. But even if you do not have a grey card shot, or a white thing shot, let us say that at the image editing stage you decide the exact adjustment color. OK now are you going to tediously repeat for every image the same group of actions, creating a new layer, filling, changing the mode to "Overlay", setting the opacity slider to a certain number? No no, let us make it easier.

Overlays with black or white

Overlays do not necessarily have to do with color casts. An overlay with black or with white might help to tonally correct a problematic photo. Before watching the next video, please make sure you understand the basic concepts of histograms exposed in Lesson 4. In the video you will watch a trick how to handle two examples of problematic images in an interesting way.

Reusing adjustment settings

For any of the adjustment tools, GIMP offers the ability to reuse settings, so as to apply them to other images/layers/drawables.

To always have in mind: on a layer vs. on a selection -- again!

As with the adjustment tools we have seen so far, a color cast adjustment may be made not on a whole layer but on a selection. This is closely related with the concept of selection, which will be explained in the next Lesson.