[Gambas-user] Image class and histogram

[Matti]

It's a histogram of pure brightness values, used in photography and in all those
image processing programs.

See http://manual.gimp.org/en/gimp-histogram-dialog.html:

"For RGB images, it is convenient to define a Value “pseudochannel ”. This is
not a real color channel: it does not reflect any information stored directly in
the image. Instead, the Value at a pixel is given by the equation V =
max(R,G,B). Essentially, the Value is what you would get at that pixel if you
converted the image to Grayscale mode."

So, my thought was wrong. You can't deduce a brightness histogram from the
histograms of R, G and B. To get that, you have to read the brightness value of
every pixel (V = max(R,G,B)) and store the values in a separate channel.


Am 13.03.2011 17:14, schrieb Benoît Minisini:
>> Great!
>> Works fine. For the channels R, G, B I get exactly the same histograms as
>> GIMP shows.
>> For the combined grayscale histogram I get a different curve, but this
>> depends on how the brightness value is computed. Have to read more.
>>
> 
> You get an histogram only for R, G, B and Alpha. What is that "combined 
> grayscale" thing?
>