Neil Barstow wrote
Now look at the histogram for colour (in Lab that's the a and b channels) it's probably under 50 percent populated. This means that what was 256 possible levels per channel is now more like 128, you just discarded 50+ percent of the possible colour/tonal steps in your image.
[note* this happens because Lab is a massive colour space]
When you convert back to RGB the colour/tonal range per channel goes back to 256 per, but it has to be interpolated up from whatever was left in Lab.
It's terrible thing to do, and is probably adding to the feeling of noise, as you now likely have posterisation to deal with.
At A3 the prints definitely look very grainy - is this normal at 400 ISO?
yes, but a trip to Lab and back would likely make it worse. aswell as causing other problems.
Neil
thanks for the info above. The reason I tried the blurring channels in LAB was because I read about it in a book where the author says that "switching to LAB is a non-destructive mode change and won't damage your photo in any way" and then goes on to describe the blurring of the a and b channels and reconversion to RGB with no mention of loss of info. I guess I won't be using this method any more.
Regards
Amanda
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