How to superimpose color images

Software G'MIC
1

Hello,

I would like to superimpose the red circles shown on the second panel below over the image in the first panel to obtain what is shown on the third panel. I was not able to accomplish this using the blend command (I assumed to be the right one). I used gimp to obtain the third panel. What would be the pipeline in gmic? Note that the red circles are antialised and kept as such in the overlay image. Input images are RGB.

overlay_montage
overlay_montage633×111 21.1 KB

Thanks for any help!

2

Like this?

image
image1282×694 32.9 KB

C:\Users\Reptorian\Downloads>gmic overlay_montage.png s x,3 rm. channels. 0 100%,100%,100%,{s#0},[255,0,0] to_rgba[0] rv[-2,-1] a[-2,-1] c blend[0,1]
[gmic]./ Start G'MIC interpreter (v.4.0.4).
[gmic]./ Input file 'overlay_montage.png' at position 0 (1 image 633x111x1x3).
[gmic]./ Split image [0] along the 'x'-axis, into 3 parts.
[gmic]./ Remove image [2] (2 images left).
[gmic]./ Keep channels 0...0 of image [1], with dirichlet boundary conditions.
[gmic]./ Input image at position 2, with values '[255,0,0]' (1 image 211x111x1x3).
[gmic]./ Force image [0] to be in RGBA mode.
[gmic]./ Reverse positions of images [1,2].
[gmic]./ Append images [1,2] along the 'c'-axis, with alignment 0.
[gmic]./ Blend images [0,1] together, using 'alpha' mode and opacity 1.
[gmic]./ Display image [0] = 'overlay_montage.png'.
[0] = 'overlay_montage.png':
  size = (211,111,1,4) [366 Kio of float32].
  data = (182,177,172,168,165,165,165,165,165,165,165,165,165,165,165,165,165,165,168,170,175,182,187,192,192,192,189,187,184,180,175,172,170,170,168,168,168,168,165,165,165,165,165,165,165,168,168,168,168,168,168,168,168,168,168,168,168,168,168,171,173,180,187,192, ... ,255,255,255,255,255,255,255,255,255,255,255,255,255,255,255,255,255,255,255,255,255,255,255,255,255,255,255,255,255,255,255,255,255,255,255,255,255,255,255,255,255,255,255,255,255,255,255,255,255,255,255,255,255,255,255,255,255,255,255,255,255,255,255,255).
  min = 0, max = 255, mean = 200.368, std = 49.5824, norm = 63178.1, coords_min = (184,22,0,0), coords_max = (128,4,0,0).
[gmic]./ End G'MIC interpreter

Other suggestions:

$ overlay_montage.png s x,3 rm. channels. 0 +negate. . a[-3--1] c f[0] [max(i0,i0#1),min(i1,i1#1),min(i2,i2#1)] rm.

gmic overlay_montage.png s x,3 rm. channels. 0 /. 255 +f[0] [255,0,0] image[0] [2],0,0,0,0,1,[1] k[0]
3

Here, I assume your foreground is not RGBA but only RGB, with the red channel being actually the alpha you want to use for the overlay.
So first we transform this foreground image to a RGBA image, then use blend alpha to merge with the background:

$ gmic background.png foreground.png channels. -3,0 f. "[ 255,0,0,A ]" blend alpha

result
result211×111 16.4 KB

1 Like
4

Thanks @Reptorian for the solutions. I tried them on the larger images, all good.

I learned a few other things as well like how to evenly split along x, s x,3 and that I can blend a RGBA with a RGB, I thought both had to have the same number of channels. And I confess that I only use full command names, e.g. -fill instead of just -f so I am not familiar with all shortcuts which forced me to visit the “list of commands” web page.

1 Like
5

Thanks @David_Tschumperle for the explanation and code. Certainly the more succinct one. Things I didn’t know one can use:

  • channles -3,0 : the -3 was new to me. The good thing is that it also works with a single channel image which is what I have for the circles so no need to make them ‘red’
  • fill “[ 255,0,0,A ]” : I always thought this had to be a fixed numeric array as in ‘[ 1,2,3,4]’. So now I know how to fill using specific channels e.g. +fill “[ R,0,B ]”

Good lessons learned!

1 Like