Tuesday, August 7, 2012
You've seen this exercise before. Are the centre objects the same? Use your eyedropper and sample a pixel. What values for RGB do you find? Are they the same?
What's going on that tricks you into thinking that they are different? If they're the same RGB values, why do they look different?
The way our eyes and brains interact, the luminance of an object is independent of the luminances of the surrounding objects. But, the brightness of an object is the perceived luminance and depends on the luminances of the surrounding objects. Thus, two objects with different surroundings could have identical luminances but different brightnesses. The bottom grouping has a light background and makes the centre look darker than the centre of the top - brightness depends on the luminance of the surrounding object.
For more information on simultaneous contrast, click here.