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color change - Printable Version

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color change - integrator - 03-16-2017

Hello,

We are using Gimp to create a transparency background from a autocad file. It works great, but we require another thing which I can't figure out. Once we create the transparency using "color to alpha" all of our walls etc... are in red (from autocad) I would like to change everything to black to stand out better in our graphics package.

Is this possible using Gimp?

Thanks


RE: color change - rich2005 - 03-16-2017

You could try color exchange Colors -> Map -> Color Exchange

looks like this: 

[attachment=382]


RE: color change - integrator - 03-16-2017

(03-16-2017, 06:43 PM)rich2005 Wrote: You could try color exchange Colors -> Map -> Color Exchange

looks like this: 

Hello,

For some reason, it doesn't allow me to select anything. This was a autocad drawing which we exported as a .png and then open in Gimp.

Thanks


RE: color change - Ofnuts - 03-16-2017

Use the alpha-lock button and bucket-fill with black. But maybe this can be avoid by changing the procedure around Color-to-alpha. Can you share an extract of the original image?


RE: color change - rich2005 - 03-16-2017

(03-16-2017, 08:24 PM)integrator Wrote: For some reason, it doesn't allow me to select anything. This was a autocad drawing which we exported as a .png and then open in Gimp.

Using color exchange you do not select anything. Click on the 'from' color and change that to red in the select dialog or use the sliders to adjust. The 'to' color should already be the default black. Then Ok that. All red in the image is changed to black - that is what you wanted isn't it?

Gimp docs (a bit dated) https://docs.gimp.org/en/plug-in-exchange.html


RE: color change - integrator - 03-17-2017

(03-16-2017, 08:51 PM)Ofnuts Wrote: Use the alpha-lock button and bucket-fill with black. But maybe this can be avoid by changing the procedure around Color-to-alpha. Can you share an extract of the original image?

Hello,

I've attached the .png file

Thanks for the help


RE: color change - rich2005 - 03-17-2017

These are the options so far:

1. Probably the one you want as Ofnuts post. Enable the alpha-lock, top of the layers dialogue and fill the layer with black. Everything will be black but the image is still RGB for annotating. Remember to un-toggle the alpha lock for further editing

2. The Color Exchange does what you asked for, changes red to black but leaves other colours.

3. A third alternative is desaturate to shades of grey Colour menu -> desaturate.

[attachment=386]

These used to be the bane of my life, Full sized drawings shrunk to A3 size for use in the field. Needed a magnifying glass to read the notes.

edit: Just a note but there is a degree of transparency remaining in the red. Can be adjusted if required.  http://i.imgur.com/kjb9Ysf.jpg

edit: another day: things are a bit quiet so a 2 minute video demo of using the alpha lock






RE: color change - Blighty - 03-18-2017

There are various ways to do this, depending on the end result that you want.

There are several shades of red; eg (RGBA)
255,0,0,128
184,0,0,255
193,0,0,145
255,0,0,255

There is also blue and cyan.

Do you want to preserve the transparency (to give shades of grey)?
Do you want to preserve the blue and cyan?
Do you want everything to be pure black?

For everything to be pure black:
1. Use the colour select tool to select the transparent area (not near any lines)
2. Invert the selection
3. Bucket fill with black


RE: color change - integrator - 03-20-2017

(03-18-2017, 08:09 AM)Blighty Wrote: There are various ways to do this, depending on the end result that you want.

There are several shades of red; eg (RGBA)
255,0,0,128
184,0,0,255
193,0,0,145
255,0,0,255

There is also blue and cyan.

Do you want to preserve the transparency (to give shades of grey)?
Do you want to preserve the blue and cyan?
Do you want everything to be pure black?

For everything to be pure black:
1. Use the colour select tool to select the transparent area (not near any lines)
2. Invert the selection
3. Bucket fill with black

Hello,
I want to keep the transparency and change the red \ blue \ cyan etc...
When you say use the colour select tool - I'm not sure what to use?

Thanks


RE: color change - rich2005 - 03-20-2017

(03-20-2017, 12:42 PM)integrator Wrote: I want to keep the transparency and change the red \ blue \ cyan etc...


watch the video as earlier post https://www.youtube.com/watch?v=I5udm03f7mw