I meant to mention that the round-off and loss of some brightness values
when editing a JPEG may or may not be a bad thing since modest losses
will not be visible in a print. Although the dynamic range of a JPEG is
very limited in comparison to what the camera can record, the dynamic
range of a print is much less than a JPEG.
When you look at the histogram of the image after doing significant
brightness/color adjustments you may see that it looks pretty "spikey".
Instead of a smooth distribution you'll see "holes" where certain
values no longer appear and spikes where round-off errors have caused
values to accumulate at that spot. If these adjustments are severe
enough it will show on the image as "posterization". It looks like a
poster painted with too few colors. But what shows up on the histogram
and the screen may not show on the print. The print doesn't have the
ability to show all the color and brightness detail in a JPEG and what's
missing might not have been visible on a print even if it was perfect.
Chuck Norcutt
Moose wrote:
> Chris Barker wrote:
>
>>I should have mentioned that, Moose -- converting to 16 bit before
>>processing a JPEG file. But I reckoned that Tim wasn't using
>>Photoshop as he did not seem to have Camera RAW (or he might not have
>>asked the question about processing RAW files).
>>
>>I understand your mention of "oddness", of the steady depletion of
>>each light value with incremental adjustment. If you use the
>>automatic buttons in Photoshop you can see the depletion in the
>>histogram.
>>
>
> Both your explanation and Chuck's are more technically explanatory than
> mine, and in that sense better, but I think mine catches the sense of
> the result. :-)
>
> Maybe the Japanese will come up with a word for it. How about one that
> means depletion of light differences, or some such?
>
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