Linear gradient and histogram

MR
Posted By
Mark_Rehmar
Feb 19, 2004
Views
290
Replies
4
Status
Closed
In trying to explain what a histogram was to a friend new to digital imaging, I opened a new document in PS CS and drew a black to white linear gradient from top to bottom, expecting to see a flat horizontal histogram.

However, the histogram is U shaped, implying that the PS linear gradient actually emphasizes the starting and ending colors.

Does anyone understand why photoshop does this to a linear gradient? Indeed, the gradient appears linear to me, so is this some compensation for the way we perceive such a variation. Very curious.

Note that I think this also would have some important implications for using linear gradients to tranparencies, or linear gradients in layer masks.

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JS
John_Slate
Feb 19, 2004
I have always believed, as you suggest, that the slightly more analog tone distribution at the ends is meant to produce a more natural look, perhaps to account for the more analog nature of human vision.

You CAN however make the gradient linear by setting smoothness to zero.
J
JasonSmith
Feb 19, 2004
Luminosity is not linear.
MR
Mark_Rehmar
Feb 19, 2004
John,

Never thought of smoothness – good idea. It’s interesting, as you note, that if you do set the smoothness to zero, while the histogram is now flat, the gradient looks pretty dull.

Jason,

As I understand, luminosity is logrithmic. Thus the reason to try to get exposures of images of limited luminosity near the right side of the histogram. If the histogram had been a logrithmic curve to the right I could have made sense of that. But the U shape seems indeed to be real, and a result of the smoothness setting.
JS
John_Slate
Feb 19, 2004
logarithmic… that’s what I meant to say, not analog.

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