Re: [CinePaint] Color Selection

On Fri, 4 Aug 2006 13:09:06 +0900
<[email protected]> wrote:

>
> I'd like to pick a color from "Color Selection" panel.
> But, It was not floating point value.
> Is this working for 8 bit interger value only ?
> 

That, in my opinion, is an interesting question.

The human eye would have great difficulty in discriminating
more that 256^3 = 16777216 different colors and so a
color selection dialog based on 8-bit values should be
sufficient.

However, strictly speaking, the selected 8-bit color value
should then be mapped into the appropriate range for the
image.

For example, is the color is 0x80, 0x80, 0x80 (hexadecimal)
and the image is 16-bit integer, the stored values should be
0x8000, 0x8000, 0x8000.  If the image is IEEE 32-bit float,
the stored values should be 0.5, 0.5, 0.5 (because 0x80
represents half of the maximum range).

But with Cinepaint this is not what happens.  If a user
selects 0x80, 0x80, 0x80 as the color, both high- and low-order
bytes are set to 0x80: 0x8080, 0x8080, 0x8080, and with
IEEE 32-bit float this becomes 0.501961, 0.501961, 0.501961.
This represents a value that is greater than half of
the maximum range.

Now, although, in a strict sense, this anomaly would
be completely unnoticed by the human eye, it is still
incorrect.

I don't know if this behavior is acceptable among image
programmers or not, but the 8-bit value selected by the
user should be accurately mapped into the appropriate
range for the image.

This behavior can be seen by creating a new 16-bit image
and then filling it with a selected 8-bit color.  Select
the Window info (View --> Window info) and place the
cursor within the image.  The indicated values will show
an inaccurate mapping.

Frank Peters


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