8 bit vs. 16 bit files for LF scans?

[Paul Schilliger]

Bill, I think this has to do with color conversion algorythms. Normally to achie ve the best possible quality, you would scan an image in RGB for inkjet or Lightjet prints or for the web, and in CMYK for pre-press. Now, if you don't know what you are scanning for yet, or are scanning for multiple purposes, the 16 bits HDR data gives you the total information available in both color environments. So converting an RGB image in CMYK from the 16 bits files should be just as good as scanning directly in CMYK. The drawback is that on some scanners, the 16 bit file is produced without the possibility of intervening on the process. If t he original is too dark, for example, it will be scanned too dark, even if the scanner had the possibility to correct the curve in 8 bits mode. So, not yet perfect.

[Paul Schilliger]

More info on this process from Scitex website at: (SOOM, Scan Once, Output Many concept)

http://www.creoscitex.com/products/input/eversmart/oXYgen.asp

[Pete Andrews]

Hi Bill. Everything I've read tells me that there is no printer or output device that can make use of 48 bit files, in fact there are only 3 file formats I know of that can store the 48 bit image format.However, as previously mentioned, it's easy to see the difference in quality that you get from doing all your manipulation and correction on a 12 or 16 bit depth image, then converting to 8 bits. For instance, if you start with a RAW scanned file from a colour negative, you can easily do the inversion and RGB channel alignment to get a perfect positive from a 12 bit/channel file. The same thing's impossible if you start with only 8 bits/channel.

I suppose the question that you need to ask and answer for yourself is: "Is this image the best I can ever get it, and will I never need, or want, to make changes to it in the future?"If you can answer "yes" to that, with 100% certainty, then you can change the mode down to 8 bits per channel and store 24 bit files with a clear conscience.OTOH, if there's any doubt, then 48 bit files would be the safer bet.West Coast Imaging have a little monogram on the philosophy of 'Sc an once, purpose many' that's relevant to this.

[Malcolm Matusky]

I always scan at 16bit (Linocolor scanner) and then open the document in photoshot, color correct in 16 bit, then convert to 8bit to do any manuiplation of the image. If you look at the histogram you have more "color data" to adjust when in 16 bit than 8.