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from color range (blue to red) to greyscale range (white to black)

This discussion is connected to the gimp-user-list.gnome.org mailing list which is provided by the GIMP developers and not related to gimpusers.com.

This is a read-only list on gimpusers.com so this discussion thread is read-only, too.

colorchange
2018-03-28 14:22:04 UTC (over 6 years ago)
postings
2

from color range (blue to red) to greyscale range (white to black)

Hello,

I hope you can help me with this issue since I could not find an apropriate solution so far. For my report I am not allowed to use diagrams with colors which are not recognisable after a black/white copy anymore, like the one attached to this message. Since a normal greyscale of the attached plot makes blue (lowest value) and red (highes value) looking similar. This is not an option. I am seeking for a quick way to, let's say translate from a color range (blue to red) to a grey scale (white to black). Since I have to do this for several images I would appreciate a quick way, if there is one...

I heard that there are more than one weighting algorithms like (R+G+B)/2 or 0,3*R+0,7*B+0,11*G and so on, but basically I would be interested in 0*Blue + maybe 30*Green + 70*Red to achieve White as a minimum (which is now marked with blue color) and black as a maximum (which is now marked with red).

Thank you in anticipation.

Best regards.

rich404
2018-03-29 14:32:55 UTC (over 6 years ago)

from color range (blue to red) to greyscale range (white to black)

Hello,

I hope you can help me with this issue since I could not find an apropriate solution so far. For my report I am not allowed to use diagrams with colors which are not recognisable after a black/white copy anymore, like the one attached to this message. Since a normal greyscale of the attached plot makes blue (lowest value) and red (highes value) looking similar. This is not an option. I am seeking for a quick way to, let's say translate from a color range (blue to red) to a grey scale (white to black). Since I have to do this for several images I would appreciate a quick way, if there is one...

I heard that there are more than one weighting algorithms like (R+G+B)/2 or 0,3*R+0,7*B+0,11*G and so on, but basically I would be interested in 0*Blue + maybe 30*Green + 70*Red to achieve White as a minimum (which is now marked with blue color) and black as a maximum (which is now marked with red).

Thank you in anticipation.

Best regards.

A possibility to try.

I know how it can be done. Use a Look-Up-Table (LUT) to replace one colour with another. Problem is I can not find a ready-made LUT.

There is a Gimp plugin gmic-gimp-qt (note the qt version) that lets you assemble a bespoke LUT see: www.gmic.eu for download and instructions.

Very tedious to set up: looks like this: https://i.imgur.com/DNM2PDK.jpg

However once done, the settings can be saved. Those settings can also be incorporated into a script (attached), which runs the gmic-gimp-qt plugin.

Unzip, pop in your gimp scripts folder. Find it bottom of the Filters menu along with gmic.

Produces this: https://i.imgur.com/I79QxDS.jpg the plugin has lots of work to do, so be patient, it gets there.

Note it is still RGB and needs converting to greyscale Image -> Mode -> Greyscale

rich: www.gimp-forum.net

colorchange
2018-03-29 15:00:53 UTC (over 6 years ago)
postings
2

from color range (blue to red) to greyscale range (white to black)

Dear rich404,

ok thank you. I will check this or maybe I can find another easier solution which is quicker to implement. Thank you very much for now.

rich404
2018-03-31 15:18:50 UTC (over 6 years ago)

from color range (blue to red) to greyscale range (white to black)

Dear rich404,

ok thank you. I will check this or maybe I can find another easier solution which is quicker to implement.
Thank you very much for now.

Hate to be beat. Lots of messing around resulting in a very simple look-up-table. A tiny png (8 pix) g2.png attached.

Again uses g'mic plugin from www.gmic.eu This time in the 'Film Emulation' section as 'User Defined'.

The gmic dialogue is in the screenshot.

As before the result is shades of gray and RGB, use Image -> Mode -> Grayscale to finish.

rich: www.gimp-forum.net

  • the LUT: g2.png
    g2.png (151 Bytes)
  • gmic dialogue
    LUT.jpg (139 KB)