Re: [CinePaint] Really basic script for batch converting.

On Mon, 23 Nov 2009, [email protected] wrote:
>
> As soon as any contrast/brightness/levels is done in 8bit more data get
> thrown away, gaps appear in the histogram no smooth undulations.

It is true that with 8-bits, some sample values could be left unused 
which were previously used.  That is true for any discrete processing.

> I've read that when these 8bit images are taken into Adobe After Effects,
> no doubt Photoshop as well and a 16bit or better project workspace is
> adopted it is said that, "something miraculous happens, the gaps (to the
> histogram) have disappeared, what's happened is the old colour values have
> been freed from the 8bit restriction and moved freely into the new range
> (16bit) evenly distributing themselves"

This sounds kind of nuts to me.  The most common way to convert from 8 
bits to 16 bits is to muliply by a constant value, or to compose the 
16-bit value with a copy of the original 8 bit value in the high and 
low byte (which accomplishes the same).  Some software may also make 
adjustments to gamma, or apply a color profile.  When converting to 32 
bit float, it is likely common to remove any gamma curve so that the 
result is linear-light.

> Is Adobe After Effects interpolating values to fill the gaps, I'm under no
> illusion that this means true native 16bit, it doesn't there were only 256
> levels to start with but does this 'interpolation' mean that further image
> manipulation does not have such a aggressive effect on the tonal values
> within the image, if now interpolated values exist to smooth the whole
> thing, depends on heavy handedness I guess.

The only way of doing this sort of 'interpolation' is to apply a 
weak low-pass filter to the image.  This results in some loss of image 
clarity.  If the image size was increased at the same time, then the 
loss of clarity would be reduced.

Bob
--
Bob Friesenhahn
[email protected], http://www.simplesystems.org/users/bfriesen/
GraphicsMagick Maintainer,    http://www.GraphicsMagick.org/

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