This image is repeated here from the last example at bottom of next page. The sliders are discussed on the next page, but the Temperature slider had a large effect, the Tint slider much less here.
The "equal" aspect is root of the "balance" we seek. As the WB is adjusted up towards 5300, the red and green and blue components converge to equal, and white, and perfect white balance (perfect because the card is known to be right, and the equal RGB result is white). The large data spike toward the right end of this histogram is a white card in the photo photographed with flash (the 5300°K result).
White is a bright gray tone where neutral is defined as equal RGB components, no color cast (specifically, white is defined as bright and equal RGB components). Because we have the known white card in the photo, we can see that in the histogram. We can't see the photo here, but an image "too blue" is made less blue and more red, to become white. Red and blue channels are shifted oppositely, here to align (balance) the RGB component peaks of a white card (which we know should be white) to remove a blue color cast. This animated histogram at right shows the concept of what White Balance actually does (the image is from page bottom of page 2). It is a difficult problem, but we have ways to make it easy. White Balance is just a fact of life in Photography. :) But once we start learning, and start seeing good color, correct color will become extremely important to us. IMO, they have not realized yet that it's not. Some users think their camera always gets color right. It's not difficult, but it is something we must tend to. This article is about how you can fix it and salvage a perfect picture. So this subject of White Balance Correction is about when you set the camera right, and still get poor colors (color at least a little wrong is very common, it's not an exact system). Auto WB does try to fix this, halfway well, but it has no clue about the right color either (Auto WB is just making some guesses, which may not be correct). There's a big difference, which photographers have to deal with. But cameras have no brain, and they do see and capture the color of real life, which we then can see incandescent is orange, which becomes a problem in our photos. This (and more) is named the Land Effect, explained by Edwin H Land (of Polaroid fame). So when we come indoors, from out of cloudy 6000°K sunlight into incandescent 3000°K light, we don't realize that incandescent is orange. Humans recognize the color that subject things should be, and we often see what we expect to see. Or rather, our brain amazingly knows to adjust our own white balance, and it can ignore these differences (in common situations).
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