Amanda I wanted to raise a point here
One that I'm sure some users will refute. Old habits die hard. Basically, do your own tests. We can't trust the histogram to tell us everything about an image - but it sure gives us an idea of the tonal integrity. amanda.darcy-at-btinternet.com (AMANDA D'ARCY)::1/12/04::7:15 am:: GMT-0000 >(I have used various techniques to reduce noise, including the options >in RAW, blurring a and b channels in LAB mode etc). An 8 bit RGB digital image is made up of 3 grayscale channels, so both colour and tone are defined together. In a full tonal range image (with a black and white point), each channel has a tonal range defined by 256 possible values. A look at the 3 channels in the histogram will often show colour/tonal detail throughout most of the range, so, generally, images use a fair amount of that possible 256 values to define tone. Take a normal RGB image (one with black shadow and white highlight in it). Check the histogram for all 3 channels. Convert it to Lab colour mode [in Lab, colour is defined separately to tone] 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. Best Regards Neil Barstow Consulting in Imaging & Colour Management http://www.colourmanagement.net/ http://www.apple.com/uk/creative/neilbarstow/ =============================================================== GO TO http://www.prodig.org for ~ GUIDELINES ~ un/SUBSCRIBING ~ ITEMS for SALE
