What is the algorithm in Image->adjustments->Level in Photoshop 7.0

Hello,

I used Image->Adjustments->Level to adjust the image histogram. As far as I know, the algorithm for the adjustment of both end side is related to 'linear stretching of histogram'. My question is what is the algorithm for the adjustment of midtone (the central triangle)? Is it logarithm transformation? Thanks for your help.

Jason

Jason,

The centre slider is for Gamma. It is the same as a single control point in the middle of a Curves adjustment.

Sliding it left or right is like moving the Curves centre control point up or down.

Unlike the (linear indeed) end sliders, this slider can't push pixels beyond both ends, because the impact of moving the centre slider becomes zero at both ends of the histogram.

Rob

Thank you Rob, is this Gamma same as the one in the 'imadjust' funcation in Matlab?

Jason

I don't know.

You can find out if there's any difference by "bending" a grey wedge (bars) about.

Anyway, it's adjusting mid-tones the most, and shadow and highlights the least.

Rob