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Merun said: You mean the 16 bit mode in Photoshop? This would mean that each color channel would be coded on 16bit ( 48bit in total ), but LCD screen and scanner are mostly 8 bit per channel ( 24bit in total ), or even 6 bit + dithering for the quick response time display. I'm not sure it's worth it..
The point isn't to be able to display it. If you have 8-bit input data, and you do filters on it (like levels and brightness), those filters only get 8-bit data and they output 8-bit data, which results in quantization.
You can see this easily: load a good 8-bit image, hit ^L, press ^1 to only show the red channel. Note that the histogram is smooth. Now do auto-levels (or brightness or any of those filters), and hit ^L, ^1 again. Notice the holes in the graph. That means there are specific, isolated color components which never occur in the image. The filter never output them because none of the 8-bit input values mapped to that 8-bit output value. This is just the most obvious side-effect of quantization; in short, the effect is that it's outputting a 7-bit image.
If you scan and work with the image as 16-bit, the filters have a lot more data to work with. Do the above on a 16-bit image (a real one, scanned as 16-bit; you can't just convert an 8-bit image!), and there'll be no holes in the graph. (Well, there are, but they're on the order of 16-bit data.) Then, when you're all done working with it, convert the image to 8-bit before exporting to the final PNG or JPEG.
This is the same principle as recording audio in 24-bit/96khz for audio processing before resampling to 16-bit/44/48khz, which also reduces quantization error.
Of course, this depends on a scanner that can give you 16-bit data. Many scanners claim that they can do this; search NewEgg for 48-bit/96bit scanners. Of course, some crappier brands may be lying, eg. if they're referring to the bit depth of the "interpolated resolution" (look mom, 19200x19200 DPI!), which is clever marketing (read: lies). Use your judgement when evaluating hardware, as always.
petopeto
You can see this easily: load a good 8-bit image, hit ^L, press ^1 to only show the red channel. Note that the histogram is smooth. Now do auto-levels (or brightness or any of those filters), and hit ^L, ^1 again. Notice the holes in the graph. That means there are specific, isolated color components which never occur in the image. The filter never output them because none of the 8-bit input values mapped to that 8-bit output value. This is just the most obvious side-effect of quantization; in short, the effect is that it's outputting a 7-bit image.
If you scan and work with the image as 16-bit, the filters have a lot more data to work with. Do the above on a 16-bit image (a real one, scanned as 16-bit; you can't just convert an 8-bit image!), and there'll be no holes in the graph. (Well, there are, but they're on the order of 16-bit data.) Then, when you're all done working with it, convert the image to 8-bit before exporting to the final PNG or JPEG.
This is the same principle as recording audio in 24-bit/96khz for audio processing before resampling to 16-bit/44/48khz, which also reduces quantization error.
Of course, this depends on a scanner that can give you 16-bit data. Many scanners claim that they can do this; search NewEgg for 48-bit/96bit scanners. Of course, some crappier brands may be lying, eg. if they're referring to the bit depth of the "interpolated resolution" (look mom, 19200x19200 DPI!), which is clever marketing (read: lies). Use your judgement when evaluating hardware, as always.