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Why is this color mapping not working?

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Why is this color mapping not working? laredotornado 13 Feb 22:55
  Why is this color mapping not working? rich404 14 Feb 09:00
  Why is this color mapping not working? Ofnuts 22 Feb 09:03
2018-02-13 22:55:22 UTC (3 months ago)
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Why is this color mapping not working?

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

2018-02-14 09:00:30 UTC (3 months ago)
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contact
Send private message

Why is this color mapping not working?

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

Not the best way, guessing some sort of selection to choose the background leaving semi-transparent pixels around the text. A jpeg especially tends to promote artefacts around text.

A better way.

Remove the background using Colour -> Colour-to-Alpha White is default

Lock the transparent pixels on the layer using the alpha lock in the layers dialogue.

Bucket fill the layer with the d3d3d3 gray.

Add a new layer under and fill with the darker gray.

Something like this is best exported as a png which because of the 2 colours is smaller than a jpeg.

screenshot and xcf is attached. xcf should still have alpha lock in place as example.

rich: www.gimp-forum.net

Ofnuts
2018-02-22 09:03:43 UTC (3 months ago)

Why is this color mapping not working?

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.