Re: [Gimp-user] Why is this color mapping not working?

[Ofnuts <ofnuts gmx com>]

On 02/13/18 23:55, laredotornado wrote:
> HI,
>
> I'm using Gimp 2.8.18 on Mac High Sierra.  I want to do what I hope is very
> simple -- switch out one color with another.  I wanted to change the white to a
> dark gray and teh black to a lighter gray.  I first changed the white color,
> which went ok.  Then, I want to change all the black to a gray color -- #D3D3D3.
> I open my image, go to the Color menu, and select "Map" and then select "Color
> Exchange".   Then I select the relevant colors and click "OK".  However the
> result (attached) is disappointing.  It is very difficult to read the numbers in
> the scale.  Am I missing something?  Or there others colors at play here?
>
> Thanks for any advice, - Dave
>
> Attachments:
> * http://www.gimpusers.com/system/attachments/815/original/scale.jpg
> * http://www.gimpusers.com/system/attachments/816/original/scale_gray.jpg
Color>Invert and then use Contrast/Brightness to adjust the result.

The catch in your method is that you have more that two colors in the 
picture, besides the two obvious ones (background and character bodies). 
There are also:

- the JPEG compression artifacts (recognizable by the 8x8 blocks pattern)

- The pixels on the edges of the characters, that can be any blend of 
the background & character colors to  create  a smooth-looking edge.