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Sven Neumann wrote:
| Hi,
| Piotr Legiecki <[EMAIL PROTECTED]> writes:
|>1)  Levels dialog - *linear* histogram as in histogram tool.
| I've done some changes and the histogram scale is now part of the
| tool-options of all tools that use a histogram. This means you can
| choose between linear and logorithmic in all those tools and the
| setting is remembered across sessions.

So, as an image processing programmer these linear and logarithmic
discussions are confusing me.  So, by linear, do you mean a histogram of
the raw image data with no transform, and by logarithmic do you mean a
histogram of the log of the raw image data?

(linear to me usually means linear-light (e.g. intensity from physics),
which would be proportional to your log scale here, assuming we are
trying to operate in sRGB space, which an inherent gamma factor of 2.2).

| What I am unsure about (and that's why I added the user list to the
| Cc:) is whether we should change the default histogram scale to
| linear. I know that you, Piotr, will vote for this change but I would
| like to get a second opinion. This perhaps also depends on what other
| apps do and since I don't have much experience with other
| applications, I am asking here. To illustrate the question, I made two
| screenshots:

Well, if I am right about your definitions above the default should be
linear.  Here is the reason:  Linear is "perceptually linear"  I.e. a
small change at any point in the histogram is perceived as a uniform
change in brightness at every point in the histogram.  E.g. 230+5 is
percieved as about the same change as 30+5.  This property doesn't hold
for linear-light (i.e. logarithmic) and thus is more difficult for use
human-types.  This property is one of the reasons non-linear-light
encoding (like sRGB and L*u'v') are such a desirable space to work in.

(For you more technically minded, perceptually linear spaces also
distribute errors (quantization or otherwise) across the entirtly of the
percieved spectrum, rather than letting them seem to all be located near
the darkest points).

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