How to keep the black outline only in a image

[meetdilip]

The attached image is the output of the Edge filter on a colour image. Wondering how I can get rid of the colour and keep the black edges only. Thanks.

[rich2005]

You can Colour -> Threshold (and adjust the slider a little)

   

another way is: Image -> Mode -> Indexed and use the black & white (1 bit) palette option

[meetdilip]

Works great!

Thanks.

[denzjos]

@Meetdilip, its not the question you asked for but you can finetune the result if needed :
- remove colors : Colours / Desaturate / Mono Mixer (use all sliders to get a satisfied result)
- smooth the drawwing with : G'Mic-Qt / Repair / Smooth [Mean-Curvature] (Time Step 30 / Iterations 13)
- duplicate the layer 5 times with layer mode 'Multiply'
- make a new layer 'New from Visible' (layer name 'Visible')
- G'Mic-Qt / Repair / Smooth [Mean-Curvature] (Time Step 30 / Iterations 13)
- duplicate the result to a new layer (layer name 'Visible copy') and set the layer mode 'Addition'
- Merge the layers 'Visible' and 'Visible copy'
- result :
   

[rich2005]

Nice result but a bit complicated.

For this type of image, an old method of smoothing.

Apply a small gaussian blur
Apply the Color -> Threshold (again)

example: https://i.imgur.com/wn1zu6a.mp4

[denzjos]

Less complicated with G'Mic-Qt / Artistic / Lineart :
   
   

[meetdilip]

Thanks @denzjos