Loss of quality after color to alpha

[nemotyrannus]

Hi , New on the forum with a problem  (sorry for my english)

After switching from 2.8 to 2.10.14 i noticed a loss of quality of the line thickness when i use the color to alpha option.

I used to draw black lines (with paths) on white background and then use the color to alpha to remove white .And then i was able to colorize a picture on another layer placed below.

There was two layers , one with black lines on transparent background and a second one , below , with colors.
It was clean when i colorized the second layer. 
Now after color to alpha ,when i remove the white , although i colorize on another layer (normal) i see that the black lines , on the first top layer , tend to disappear and get very thin when i color and pass on them . It becomes very pixelized too .

Is there a way to counter this effect ?
Has someone faced the same issue ?


Ps
I don't know if there is a connection but i also noticed after switching from 2.8 to 2.10.14 that thickness is not the same .

As an exemple a 2 pixel size brush/path is now way thiner than it was before.

[Ofnuts]

You can draw your lines on a transparent layer, and then completely avoid the Color-to-alpha step.

This said in 2.8 there were two ways to remove a color, Color-to-alpha and buclet-fill in "Color erase" mode, that gave identical results. The two modes still exist in 2.10, but if C2A gives a different result, bucket-fill in "Color Erase" mode gives the same result as before.

[rich2005]

Gimp 2.10 has more brush tool options than Gimp 2.8  One of them is Force. Default value is 50. A comparison suggests a value of 100 gives a Gimp 2.8 / 2.10 equivalence.

   

[nemotyrannus]

(03-18-2020, 11:10 PM)Ofnuts Wrote: You can draw your lines on a transparent layer, and then completely avoid the Color-to-alpha step.

This said in 2.8 there were two ways to remove a color, Color-to-alpha and buclet-fill in "Color erase" mode, that gave identical results. The two modes still exist in 2.10, but if C2A gives a different result, bucket-fill in  "Color Erase" mode gives the same result as before.

Yes i can draw on a transparent layer however it is difficult to see anything , because when we draw we tend to correct , draw things again , etc... 
Working on a white background is necessary. And not on another layer.

Thanks for answering !

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(03-19-2020, 10:37 AM)rich2005 Wrote: Gimp 2.10 has more brush tool options than Gimp 2.8  One of them is Force. Default value is 50. A comparison suggests a value of 100 gives a Gimp 2.8 / 2.10 equivalence.

I don't think it is abut force or the brush density. It looks more like a size difference.

Maybe it is really about force But Even if it were , there is no way to correct this with "path" which is the tool we use in order to get clean geometrical lines (not paintbrush/pencil )

[Ofnuts]

(03-19-2020, 03:53 PM)nemotyrannus Wrote:

(03-18-2020, 11:10 PM)Ofnuts Wrote: You can draw your lines on a transparent layer, and then completely avoid the Color-to-alpha step.

This said in 2.8 there were two ways to remove a color, Color-to-alpha and buclet-fill in "Color erase" mode, that gave identical results. The two modes still exist in 2.10, but if C2A gives a different result, bucket-fill in  "Color Erase" mode gives the same result as before.

Yes i can draw on a transparent layer however it is difficult to see anything , because when we draw we tend to correct , draw things again , etc... 
Working on a white background is necessary. And not on another layer.

Thanks for answering !

Painting on a transparent layer with a white layer under it gives exactly the same result as painting directly on a white layer. If you can show me this is different the Gimp developers have a major bug in their hands.

[rich2005]

Quote:Maybe it is really about force But Even if it were , there is no way to correct this with "path" which is the tool we use in order to get clean geometrical lines (not paintbrush/pencil )

If you are confined to stroking a path with a one or two pixel size (not using the paint tool) then the difference between Gimp 2.8 and Gimp 2.10 might be either a design decision or a bug. Either way worth bringing up with the developers.  see: https://gitlab.gnome.org/GNOME/gimp/issues/


The same exists in Gimp 2.10.18 so not just a Gimp 2.10.14 thing.

You can get a denser line  for the  fill tool boundary by repeating the stroke path operation 2 or 3 times. Use a keyboard shortcut to expedite 

example: https://i.imgur.com/ogFrb7C.mp4