Re: [Gimp-user] When black and white is not black and white

["Alex Vergara Gil" <alex vergara dic centis cu>]

You may try Colors -> Component -> Decompose, then select LAB space, BW 
image is the L, thats a lot better than anything else I have tried

Regards 

-----Original Message-----
From: Lancer <forums gimpusers com>
To: gimp-user-list gnome org
Cc: notifications gimpusers com
Date: Tue, 06 Jun 2017 06:02:29 +0200
Subject: [Gimp-user] When black and white is not black and white

I am a school teacher. One of the checks I ask students to do in order to 
test
the contrast of their graphics work, is to convert the images to grayscale 
and
see whether images are still clear.

There are two methods students are using to convert their images to 
grayscale
for this test...


Method 1: flatten image, then Colors > Hue-Saturation => slide the 
saturation
slider down to zero.
Method 2: image => mode => grayscale

Either of these methods results in a grayscale image, but the grays are not
exactly the same.

For example, if I have absolute red (#FF0000) next to blue, the 
grayscaled-blue
may match the grayscaled-red depending on the tone *and* the method used.
Method 1: Absolute red (#FF0000) will grayscale-match absolute blue 
(#0000FF)
Method 2: Absolute red (#FF0000) will grayscale-match a slightly lighter 
shade
of blue  (#2626FF)

Why are the two methods of grayscale having a different result? I would have
thought that conversion to grayscale would be the same process as dragging 
down
the saturation of an image.

...and given that they are different, which is the better method to use in 
terms
of testing for contrast in media assignments?

--
Lancer (via www.gimpusers.com/forums)
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