As a grey-beard engineer who has been designing computers and software since before the PCjr was a new idea, I have to say that this book is very impressive. It has been a treat to read something from a writer that is technically knowledgeable in addition to knowing his photography. So many books and teachers these days fall back on "because that's what I was taught" ...
This past weekend I took a class at the Panasonic Digital Photo Academy and the instructor told us to "never use Levels, as it will comb even a 16-bit image." I know that it's bad manners to argue with the teacher, but I tried to tell him it was just a cached image that wasn't getting redrawn in real time. This is because I had just read the section on pages 183-184 that describes exactly that. And he told me I was wrong.
Can you please provide some reference on this subject other than in the book? Thanks.
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CS3 Histogram Caching Question
Started by M. Harry Trask, Aug 28 2007 08:04 AM
1 reply to this topic
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Posted 28 August 2007 - 08:04 AM
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Posted 28 August 2007 - 09:39 AM
M. Harry Trask, on Aug 28 2007, 09:04 AM, said:
Can you please provide some reference on this subject other than in the book? Thanks.
Try this from the Photoshop CS3 Help document. Search for "histogram cache"
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Refresh the histogram display
When a histogram is read from a cache instead of the document’s current state, the Cached Data Warning icon appears in the Histogram palette. Histograms based on the image cache are displayed faster and are based on a representative sampling of pixels in the image. You can set the cache level (from 2 to 8) in the Performance preference.
To refresh the histogram so that it displays all of the pixels of the original image in its current state, do one of the following:
Double-click anywhere in the histogram.
Click the Cached Data Warning icon .
Click the Uncached Refresh button .
Choose Uncached Refresh from the Histogram palette menu.
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Not having been there, I'm reluctant to criticize, but if the instructor was really saying A: PS does not use caches for faster histogram display or B: the cached histogram view with the warning icon is an accurate indicator of data clipping or C: a Levels adjustment in 16 bit causes combing in the non-cached histogram, then you should get your money back from that class.
There are many reasons not to use Levels on 8 or 16 bit images, but this is not one of them.
