Re: [Gimp-user] Histogramm -- values

[scl <scl gplus gmail com>]

On 13.11.2013 at 9:38 PM Øyvind Kolås 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
> > see http://en.wikipedia.org/wiki/Luminance_%28relative%29.
> >
> > 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.

Hi,

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?

Kind regards,

Sven