Levels histogram oddity in CS

SS
Posted By
Susan_S.
Jun 8, 2004
Views
273
Replies
6
Status
Closed
I’ve just noticed something rather odd. Am I going nuts, do I need to delete my preferences or is this universal?. Can anyone else replicate this? And if they can, is there any good reason for this difference in behaviour between 16 and 8 bit mode?

The behaviour:
1.On an 8 bit RGB image, load the RGB channel as a selection (option-command-shift-~ click on the image).
2. Image/adjustments/levels – the histogram shown in the levels dialogue will be just the histogram of the selected portion of the image.
3.Hit cancel and then add a levels adjustment layer, same selection. Again the levels histogram shows just the histogram for the selection.

4. Now repeat the exercise on a RGB 16 bit image. Same selection, use Image/adjustment/levels – the RGB histogram in the levels dialogue gives same result as with eight bit – histogram of the selected pixels only.
5. But with a levels adjustment layer in 16 bit mode the levels dialogue shows the histogram of the whole image…NOT just the selected pixels…

(and yes this is of vaguely practical importance to me!)

I’m using CS on a 600Mhz G3 imac, 756Mb RAM running 10.3.4. In case that makes a difference.

Susan S.

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BF
Bruce_Fraser
Jun 8, 2004
I can reproduce this. It looks like the 16-bit version ignores the layer mask when it builds the histogram.
SS
Susan_S.
Jun 8, 2004
Thanks Bruce – is this a feature or a bug? And is there any way around it?

Susan S.
BF
Bruce_Fraser
Jun 8, 2004
If it’s a feature, it certainly needs explaining!

Loading the layer mask as a selection doesn’t work on the Levels histogram, but it does at least make the Histogram palette show the correct histogram. That’s as close to a workaround as I’ve been able to get.
SS
Susan_S.
Jun 8, 2004
Hmmm. I guess I’ll just have to live with it for now – I have an action which sets up a series of levels adjustment layers targeting highlights, shadows and midtones (roughly) and without being able to see the histograms accurately, it makes them a bit hard to tweak. I can still use it in 8 bit, and to be honest shadows /highlights can do just about everything I was doing with the levels layers anyway – only I find it harder to control as I’m not used to it yet.

Susan S.
CC
Chris_Cox
Jun 10, 2004
Yeah, that sounds like a bug.
SS
Susan_S.
Jun 10, 2004
Thanks for confirming that Chris. As a relatively new user of photoshop (I’ve just switched from Elements), it was a bit disconcerting – I wasn’t sure whether I was being an idiot or there was a problem with the install. It’s comforting to know that neither applies. (Is there a reward for finding a Real Bug?!!).

Susan S

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