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Major corrections in Curves and Levels dialogs.

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3F938437.60501@sci.pam.szcz... 07 Oct 20:15
  Major corrections in Curves and Levels dialogs. Sven Neumann 24 Oct 10:39
   Major corrections in Curves and Levels dialogs. Daniel Rogers 24 Oct 17:29
    Major corrections in Curves and Levels dialogs. Tor Lillqvist 25 Oct 09:01
3F94D25F.1090708@sci.pam.sz... 07 Oct 20:15
  Major corrections in Curves and Levels dialogs. Sven Neumann 24 Oct 12:44
Sven Neumann
2003-10-24 10:39:06 UTC (over 20 years ago)

Major corrections in Curves and Levels dialogs.

Hi,

Piotr Legiecki 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.

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:

http://sven.gimp.org/gimp-histogram-linear.png http://sven.gimp.org/gimp-histogram-logarithmic.png

Both options are available; the question is just which should be the default? We could even have different defaults for histogram, levels and threshold tool but I think that would go too far...

Sven

Sven Neumann
2003-10-24 12:44:43 UTC (over 20 years ago)

Major corrections in Curves and Levels dialogs.

Hi,

for those of you who want to follow the discussion about improvements to the Levels and Curves tools, here's a list of relevant bug reports with some comments. I'm adding the user list to the Cc: since feedback from users would be very helpful at this.

Improve color pickers in Levels tool http://bugzilla.gnome.org/show_bug.cgi?id=125303

I would very much appreciate some feedback on this. The bug report is suggesting that the current behaviour of the gray point picker is incorrect. I tend to agree with this argument but I would like to hear other people's opinions on this.

Curves dialog http://bugzilla.gnome.org/show_bug.cgi?id=125305

I don't understand what this report is talking about but perhaps one of you can enlighten us?

Linear histogram in Levels tool http://bugzilla.gnome.org/show_bug.cgi?id=125306

This one has been addressed in the meantime.

Improve Histogram with Luminance Channel http://bugzilla.gnome.org/show_bug.cgi?id=109161

A luminance channel (is that the correct term at all?) would indeed be a useful addition. Adding it to the Histogram means adding it to the Levels and Curves tools as well. This could be a rather trivial change but it might also turn out to be a lot more complicated then it seems. I am not entirely sure how much code depends on details of the GimpHistogramChannel enum.

Sven

Daniel Rogers
2003-10-24 17:29:06 UTC (over 20 years ago)

Major corrections in Curves and Levels dialogs.

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Sven Neumann wrote: | Hi,
|
| Piotr Legiecki 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).

- --
Dan
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Tor Lillqvist
2003-10-25 09:01:58 UTC (over 20 years ago)

Major corrections in Curves and Levels dialogs.

Just my 2 euro cents: The "linear" histogram illustration Sven provided looks a lot more like histograms of typical images do in other applications than the "logarithmic" one.

I have often wondered why GIMP's (traditional logarithmic) histograms look so different than the ones you see in other (commercial) software. So my guess is that "linear" is what people expect.

--tml