Re: [Gimp-user] Histogramm -- values

On 11/14/2013 08:16 AM, scl wrote:
On 13.11.2013 at 9:38 PM �yvind Kol�s wrote:> On Tue, Nov 12, 2013 at 4:39 AM, Wolfgang Hugemann <Auto hugemann 
de> wrote:
However, there seems to be no way to display the histogramm in terms of
brightness in Gimp (?). The "value" seems to be just max(R,G,B). But
luminance is generally caculated by
Y = 0.2126 R + 0.7152 G + 0.0722 B

Wouldn't it make sense to offer this option?

In my opinion, the (still) widespread use of value = max(max(r,g),b)
is a remnant of 8bit image processing centric performance short-cuts.
We would be better off by using luminance in most or all the cases
where this approach is currently used.


we had a similar discussion about the inconsistent use of the word
'value' in IRC ca. 4 months ago. Currently this word appears at various
places in GIMP:
- in the Levels Tool as a channel,
- in the Curves Tool as a channel,
- in the Colors Menu as item 'Invert value'
- in the dockable Histogram dialog as a channel (but there's also a channel 'RGB'),
- in the dockable Pointer dialog as component of the HSV color model,
- in the dockable Sample Points dialog as component of the HSV color model,
- in the Color Picker tools info window as component of the HSV color model,
- in the Change Color dialog as component of the HSV color model (V slider),
- as result layer in Color/Decompose/HSV, HSL,
- as parameter in Filters/Distorts/Value propagate,
- as parameter in Filters/Decor/Add border,
- in various places all of the program in its original meaning
(set/increase/decrease/minimize/etc. value) and
- in various places of the help.

... and not all seem to have the same meaning as we found out that time.
There also seems to be no consensus about the meaning of this word
in the graphics industry, even when used as abbreviation for
'tonal value': some mean the brightness of a given pixel, others
the perceptual brightness of each color (yellow->light, blue->dark).

I'm for using the words value, tonal value, brightness, lightness etc.
consistently to avoid further confusion.
What are the 'officially defined' or 'most commonly used' names and
meanings in these contexts for you, the users?

For me, "value" means how white or black the pixel is. This assumes an implicit map to gray scale.  I think 
that this meaning remains the same even if you choose different ways to map to gray. So, users should be made aware of, 
and be able to select a mapping/a default mapping.

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