Contrast is Relative
I used to think that for a image to have strong contrast, the histogram needs to looks like this: That is, good portions of pixels must inhabit both the black and the white zones. But images like this have changed my mind: Here the blacks are dark (solid black, in fact) but the brightest portions of this image – the white of his eye – is only at about 70% brightness. In short, I’ve started thinking about contrast in much more