Digital BW, The Print

Will any future digital camera ever shoot in 32 bit?
Mark

On Apr 10, 2007, at 11:21 AM, dealy663 wrote:

> A little bit of computer science here.
>
> An 8 bit BW file can have at most 256 levels of gray tones, a 16 bit
> file can have 65536 independent tones. Converting from 8 to 16 bit
> simply maps those original 256 tones into the 65536 space. If you had
> a linear gradient going from black to white at the start it would
> appear exactly the same after the conversion. You would still have 256
> independent tones. However you would also have room between each tone,
> 256 blank spots with no gray vales on either side. By this I mean that
> for the gray value that was originally 128 in the 8 bit file it would
> now be 32768. The difference being that in the 8 bit file there were
> picture elements represented by values 127 and 129. While in the 16
> bit file those values would be represented by 32512 and 330224, there
> would be no pixels in the image with values between 32768 and these
> other two numbers.
>
> Next lets say that you adjust the global contrast of your image. In a
> simplified algorithm, an increase in contrast makes the values below
> the midpoint (128 8-bit) darker and the values above the midpoint
> lighter. In an 8 bit file if we subtract 1 from each value less than
> 128 then we now have 126 tones where we had 127 tones before the
> subtraction. This is because the pixels that were formerly at value 1
> are now at zero along with all the pixels that were previously at
> zero. The same logic applies above the midpoint, so where we
> originally had 256 tones before the contrast adjustment we now have
> 254. In a 16 bit file applying the same type of correction still
> leaves you with the original 256 independent tones, because there was
> 256 bits of headroom between each original pixel value. You would have
> to adjust the contrast by more than 255 points before you started
> reducing the number of tones in your image.
>
> The scenario I've described above leads to the posterization that we
> see when making large adjustments in 8-bit files. It is not true that
> all image editing leads to the loss of data, but large movements
> certainly can. There are other issues with 8 vs 16 bit related to
> rounding errors also.
>
> With all that said, I rarely change my 8-bit files to 16-bit before
> editing. I would only do so if there was something really wrong with
> my exposure and I needed to make large adjustments to the file.
>
> Hope I didn't confuse the issue too much.
>
> Derek
>
>
>
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