On Fri, 2005-07-22 at 17:03, Rob Studdert wrote: > ... > whether 12 bits per colour channel would make make an appreciable visible > difference given the dynamics of current display technology is arguable > (given > the relatively low contrast ratios of even the best TFT displays). I'd be > happy > to read some practical reviews.
Just look at the dark areas of a DVD movie (The Matrix is a good choice), you'll clearly see that 256 levels are not enough. These 256 levels are not evenly distributed across the brightness range, after gamma correction there are very few levels in the dark range. 12 bits would be 4 times better and probably OK > Generally dither is only beneficial in print systems without the capability > to > modulate pixel density. Dither is pointless if it only serves to reduce the > print sharpness and acutance. RGB direct to photo paper print systems would > not > benefit from dither so they don't use it, ink jet print systems can benefit > and > their drivers generally employ dither of some form. Surprise. Dithering generates extra perceived levels at the expense of added (temporal or spacial) noise. RGB to photo paper systems do temporal dithering (that obviously is not visible on paper), this could be done to 10 or 12 bits values at no expense. Printer drivers do a lot of dithering and could do it a bit more to achieve more than 256 levels. Rough dithering, like for getting 256 levels out of 2, is very visible; more subtle dithering like for getting 4096 levels out of 256 is hardly visible as you're mixing colors that are already quite similar. > Any photographer who currently wishes to ensure that their archived digital > images are able to take full advantage of future printing technologies need > only save them in an image format which can support 16 bit per colour channel > wide gamut colour space. Yes. The problem is that the (time, complexity and money) expense from using RAW is not acceptable for many people. There should be a compressed 16 bits image format both in our cameras and in every piece of software, something as universal and easy to use as jpg. A floating point format like the one used in Film Gimp (now called CinePaint http://cinepaint.sourceforge.net/) would be even better. Play a bit with it, you'll be amazed: open one of your photographs; convert it to floating point; reduce contrast to almost 0 until everything looks like a single shade of gray; save it to disk and close it; open it again; increase contrast; you get your old image back without any visible loss. Joaquim
