Here's a different method for which you will need gimp (I used a 2.10 version) and also G'IMIC Qt which you can get as a plugin for Gimp. If you haven't got G'IMIC I'm sure someone will tell you how to get it.
Open your 'flowery flowers template.jpg' in gimp.
Duplicate the layer, because keeping the original is always a good idea.
Make a black and white layer of the flowers, this is your lineart layer:
On the duplicate layer do:
Colours -> Desaturate -> Desaturate
Mode: Luma
Colours -> Curves
Drag the bottom left of the line to the right until the greys look black, see the red arrow in my example attached below.
Make a colour spots layer:
Make a new transparent layer:
In the new transparent layer:
With the pencil tool draw black blobs/spots in all the areas you want to fill with black.
With the pencil tool draw some red spots/lines in the background you don't want to fill with black.
See the my attached colour spots below for an example.
Turn off the visibility of all layers except for your lineart layer and colour spots layer.
The colour spots layer should be above the lineart layer in the layer stack.
Use gmic colourise lineart to colour in the flowers:
Filters -> G'IMIC Qt -> Black & White -> Colorize Lineart (Propagation)
Layers ordering:
Input layers: Color Spots + Lineart
Output layers: Extrapolated Colours + Lineart
Extrapolate Colors as: One Layer per Single Color
Smoothness: 0.05
Input / Output:
Input layers: All visible
Output mode: New layer(s)
Preview: Mode: 1st output (default)
When G'IMIC Qt has finished you should have three new layers from top down in the layer stack:
The background all coloured red
Areas of flowers filled in black on a transparent background
Lineart
Turn off visibility of all layers except:
Areas of flowers filled in black on a transparent background
Lineart
That's the result, mine is attached below, you can export it e.g.
File -> Export
Or if you want it as one layer:
Layer -> New from visible
Or you could merge the two layers.
Open your 'flowery flowers template.jpg' in gimp.
Duplicate the layer, because keeping the original is always a good idea.
Make a black and white layer of the flowers, this is your lineart layer:
On the duplicate layer do:
Colours -> Desaturate -> Desaturate
Mode: Luma
Colours -> Curves
Drag the bottom left of the line to the right until the greys look black, see the red arrow in my example attached below.
Make a colour spots layer:
Make a new transparent layer:
In the new transparent layer:
With the pencil tool draw black blobs/spots in all the areas you want to fill with black.
With the pencil tool draw some red spots/lines in the background you don't want to fill with black.
See the my attached colour spots below for an example.
Turn off the visibility of all layers except for your lineart layer and colour spots layer.
The colour spots layer should be above the lineart layer in the layer stack.
Use gmic colourise lineart to colour in the flowers:
Filters -> G'IMIC Qt -> Black & White -> Colorize Lineart (Propagation)
Layers ordering:
Input layers: Color Spots + Lineart
Output layers: Extrapolated Colours + Lineart
Extrapolate Colors as: One Layer per Single Color
Smoothness: 0.05
Input / Output:
Input layers: All visible
Output mode: New layer(s)
Preview: Mode: 1st output (default)
When G'IMIC Qt has finished you should have three new layers from top down in the layer stack:
The background all coloured red
Areas of flowers filled in black on a transparent background
Lineart
Turn off visibility of all layers except:
Areas of flowers filled in black on a transparent background
Lineart
That's the result, mine is attached below, you can export it e.g.
File -> Export
Or if you want it as one layer:
Layer -> New from visible
Or you could merge the two layers.