Find nearest point horizontal in imagemagick? - imagemagick

Question

I'm trying to find the nearest point to the point (red in this case) in this image. In this image this output find the first line point from right
how I could do this
output
Please help me.

Answer 1

This looks fun! Let's dump the image to text using ImageMagick:
convert image.png txt:
# ImageMagick pixel enumeration: 337,218,65535,srgb
0,0: (65535,65535,65535) #FFFFFF white
1,0: (65535,65535,65535) #FFFFFF white
2,0: (65535,65535,65535) #FFFFFF white
3,0: (65535,65535,65535) #FFFFFF white
4,0: (65535,65535,65535) #FFFFFF white
...
...
221,79: (0,0,0) #000000 black
221,80: (0,0,0) #000000 black
221,81: (0,0,0) #000000 black
221,82: (0,0,0) #000000 black
...
...
Ok, now let's use awk to find all black pixels and print their (x,y) coordinates:
convert image.png txt: | awk -F'[,:]' '/black/{x=$1;y=$2;print x,y}'
221 79
221 80
221 81
221 82
221 83
221 84
...
...
Ok, now let's tell awk where the red pixel is by passing in rx (red x-coordinate) and ry (red y-coordinate). Then also, calculate the sum of the squares of the x-distance and y-distance from red to each black pixel. When it is less (i.e. nearer) than any seen so far, save the location. Print the nearest location at the end.
convert image.png txt: | awk -F'[,:]' -v rx=318 -v ry=127 '
BEGIN{m=999999}
/black/{
x=$1; y=$2; d2=(rx-x)*(rx-x)+(ry-y)*(ry-y)
if(d2<m){m=d2;xm=x;ym=y}
}
END{print xm,ym}'
277 127
So, that is the answer... (277,127). Let's check it by drawing a cyan circle there:
convert image.png -fill cyan -draw "circle 277,127 277,132" check.png
On re-reading the question, I note that you actually only want the horizontally closest point whereas my solution above caters for the general case in any direction. If you just want horizontal offset, and you know the horizontal line is at y-coordinate 127, you can just extract that specific row from the image and simplify things like this:
convert image.png -crop x1+0+127 txt: | awk -F'[,:]' -v rx=318 '
BEGIN{m=999999} /black/{x=$1;d=(rx-x)*(rx-x);if(d<m){m=d;xm=x}} END{print xm}'
277
If you don't like awk, you can just do it by eyeball...
convert image.png -crop x1+0+127 txt: | grep -E "black|red"
221,0: (0,0,0) #000000 black
277,0: (0,0,0) #000000 black <--- nearest black to red
314,0: (65535,0,0) #FF0000 red
315,0: (65535,0,0) #FF0000 red
316,0: (65535,0,0) #FF0000 red
317,0: (65535,0,0) #FF0000 red
318,0: (65535,0,0) #FF0000 red
319,0: (65535,0,0) #FF0000 red
320,0: (65535,0,0) #FF0000 red
How did I find the coordinates of the red pixel? I used ImageMagick's sub-image search looking for a red pixel like this:
compare -metric rmse -subimage-search -dissimilarity-threshold 1 image.png \( -size 1x1 xc:red \) null:
0 (0) # 317,121
Notes:
I just used the sum of the squares rather than the square root of the sum of the squares because it is computationally faster and the results are the same because it holds that if a>b, then a * a > b * b in this case.
I used slightly different rx and ry from those generated by the sub-image search because OP says he had the coordinates and the ones found by sub-image search don't find the exact centre of the rather large red blob, but instead the top-leftmost edge of the red blob.