Mixing
ImageMagick using alpha channel to control calculating min, max and mean image values
ImageMagick command identify prints to screen the min, max and mean values of all the pixels in an image - e.g. for an RGB TIF image we can see the mean thus:
identify -verbose -quiet image.tif | grep mean
which lists (for Red Green Blue and Gray):
mean: 122.974 (0.48225)
mean: 107.722 (0.422438)
mean: 84.1278 (0.329913)
mean: 104.941 (0.411534)
Q: if my image has a boolean alpha channel can I use it to limit the calculations to include only those pixels where alpha was set to 1?
I tried using the clip-mask option with either leading - or + but the means didn't change as would be expected.
command-line imagemagick alpha
asked Nov 19 '18 at 19:30
GavinBrelstaffGavinBrelstaff
1,79411131
add a comment |
ImageMagick command identify prints to screen the min, max and mean values of all the pixels in an image - e.g. for an RGB TIF image we can see the mean thus:
identify -verbose -quiet image.tif | grep mean
which lists (for Red Green Blue and Gray):
mean: 122.974 (0.48225)
mean: 107.722 (0.422438)
mean: 84.1278 (0.329913)
mean: 104.941 (0.411534)
Q: if my image has a boolean alpha channel can I use it to limit the calculations to include only those pixels where alpha was set to 1?
I tried using the clip-mask option with either leading - or + but the means didn't change as would be expected.
command-line imagemagick alpha
asked Nov 19 '18 at 19:30
GavinBrelstaffGavinBrelstaff
1,79411131
I'm not at a computer, but you know how to count the on and off alpha pixels, yes? And if you multiply the RGB channels by the alpha channel all transparent pixels will go to black so you can find the max. And if you multiply by (255-alpha) you can find the min.
– Mark Setchell
Nov 19 '18 at 21:25
1
Good idea, Mark!
– fmw42
Nov 19 '18 at 23:35
thanks also to Mark!
– GavinBrelstaff
Nov 20 '18 at 17:16
add a comment |
ImageMagick command identify prints to screen the min, max and mean values of all the pixels in an image - e.g. for an RGB TIF image we can see the mean thus:
identify -verbose -quiet image.tif | grep mean
which lists (for Red Green Blue and Gray):
mean: 122.974 (0.48225)
mean: 107.722 (0.422438)
mean: 84.1278 (0.329913)
mean: 104.941 (0.411534)
Q: if my image has a boolean alpha channel can I use it to limit the calculations to include only those pixels where alpha was set to 1?
I tried using the clip-mask option with either leading - or + but the means didn't change as would be expected.
command-line imagemagick alpha
asked Nov 19 '18 at 19:30
GavinBrelstaffGavinBrelstaff
1,79411131
ImageMagick command identify prints to screen the min, max and mean values of all the pixels in an image - e.g. for an RGB TIF image we can see the mean thus:
identify -verbose -quiet image.tif | grep mean
which lists (for Red Green Blue and Gray):
mean: 122.974 (0.48225)
mean: 107.722 (0.422438)
mean: 84.1278 (0.329913)
mean: 104.941 (0.411534)
Q: if my image has a boolean alpha channel can I use it to limit the calculations to include only those pixels where alpha was set to 1?
I tried using the clip-mask option with either leading - or + but the means didn't change as would be expected.
command-line imagemagick alpha
command-line imagemagick alpha
asked Nov 19 '18 at 19:30
GavinBrelstaffGavinBrelstaff
1,79411131
asked Nov 19 '18 at 19:30
GavinBrelstaffGavinBrelstaff
1,79411131
edited Nov 19 '18 at 19:43
GavinBrelstaff
asked Nov 19 '18 at 19:30
GavinBrelstaffGavinBrelstaff
1,79411131
asked Nov 19 '18 at 19:30
GavinBrelstaffGavinBrelstaff
1,79411131
asked Nov 19 '18 at 19:30
GavinBrelstaffGavinBrelstaff
1,79411131
1,79411131
I'm not at a computer, but you know how to count the on and off alpha pixels, yes? And if you multiply the RGB channels by the alpha channel all transparent pixels will go to black so you can find the max. And if you multiply by (255-alpha) you can find the min.
– Mark Setchell
Nov 19 '18 at 21:25
1
Good idea, Mark!
– fmw42
Nov 19 '18 at 23:35
thanks also to Mark!
– GavinBrelstaff
Nov 20 '18 at 17:16
add a comment |
I'm not at a computer, but you know how to count the on and off alpha pixels, yes? And if you multiply the RGB channels by the alpha channel all transparent pixels will go to black so you can find the max. And if you multiply by (255-alpha) you can find the min.
– Mark Setchell
Nov 19 '18 at 21:25
1
Good idea, Mark!
– fmw42
Nov 19 '18 at 23:35
thanks also to Mark!
– GavinBrelstaff
Nov 20 '18 at 17:16
I'm not at a computer, but you know how to count the on and off alpha pixels, yes? And if you multiply the RGB channels by the alpha channel all transparent pixels will go to black so you can find the max. And if you multiply by (255-alpha) you can find the min.
– Mark Setchell
Nov 19 '18 at 21:25
I'm not at a computer, but you know how to count the on and off alpha pixels, yes? And if you multiply the RGB channels by the alpha channel all transparent pixels will go to black so you can find the max. And if you multiply by (255-alpha) you can find the min.
– Mark Setchell
Nov 19 '18 at 21:25
1
1
Good idea, Mark!
– fmw42
Nov 19 '18 at 23:35
Good idea, Mark!
– fmw42
Nov 19 '18 at 23:35
thanks also to Mark!
– GavinBrelstaff
Nov 20 '18 at 17:16
thanks also to Mark!
– GavinBrelstaff
Nov 20 '18 at 17:16
add a comment |
1 Answer
1
active
oldest
votes
In ImageMagick, the -scale 1x1! function can be used to compute the mean without including alpha so that you get the mean of only opaque values. So you could do the following:
Create test transparent image:
convert logo: -transparent white logot.png
Compute mean values:
convert logot.png -scale 1x1! -alpha off -format "%[fx:255*u.r], %[fx:255*u.g], %[fx:255*u.b]" info:
100.202, 81.4747, 98.6342
Alternately, you can use the alpha channel as a mask to get the means. You compute the mean of each channel without the alpha channel and the background under the alpha set to black. Then compute the mean of the alpha channel. Then divide each channel mean by the mean of the alpha channel.
convert logo: -transparent white logot.png
convert logot.png -alpha extract alpha.png
means_rgb=$(convert logot.png -background black -alpha background -alpha off -format "%[fx:mean.r],%[fx:mean.g],%[fx:mean.b]" info:)
mean_r=$(echo $means_rgb | cut -d, -f1)
mean_g=$(echo $means_rgb | cut -d, -f2)
mean_b=$(echo $means_rgb | cut -d, -f3)
mean_alpha=$(convert alpha.png -format "%[fx:mean]" info:)
mean_r=$(convert xc: -format "%[fx:255*$mean_r/$mean_alpha]" info:)
mean_g=$(convert xc: -format "%[fx:255*$mean_g/$mean_alpha]" info:)
mean_b=$(convert xc: -format "%[fx:255*$mean_b/$mean_alpha]" info:)
echo "$mean_r, $mean_g, $mean_b"
100.203, 81.4768, 98.6362
To get the min and max, taking the cue from Mark Setchell's idea:
convert logot.png -background black -alpha background -alpha off -format "%[fx:255*maxima.r], %[fx:255*maxima.g], %[fx:255*maxima.b]n" info:
255, 250, 244
convert logot.png -background white -alpha background -alpha off -format "%[fx:255*minima.r], %[fx:255*minima.g], %[fx:255*minima.b]n" info:
4, 0, 0
answered Nov 19 '18 at 19:50
fmw42fmw42
7,47341427
Yeah but unfortunately the-scale 1x1!trick doesn't work for minimum.
– GavinBrelstaff
Nov 19 '18 at 19:56
I have modified my answer to include computing the max and min values using a modification of the suggestion from Mark Setchell.
– fmw42
Nov 19 '18 at 23:44
add a comment |
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1 Answer
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In ImageMagick, the -scale 1x1! function can be used to compute the mean without including alpha so that you get the mean of only opaque values. So you could do the following:
Create test transparent image:
convert logo: -transparent white logot.png
Compute mean values:
convert logot.png -scale 1x1! -alpha off -format "%[fx:255*u.r], %[fx:255*u.g], %[fx:255*u.b]" info:
100.202, 81.4747, 98.6342
Alternately, you can use the alpha channel as a mask to get the means. You compute the mean of each channel without the alpha channel and the background under the alpha set to black. Then compute the mean of the alpha channel. Then divide each channel mean by the mean of the alpha channel.
convert logo: -transparent white logot.png
convert logot.png -alpha extract alpha.png
means_rgb=$(convert logot.png -background black -alpha background -alpha off -format "%[fx:mean.r],%[fx:mean.g],%[fx:mean.b]" info:)
mean_r=$(echo $means_rgb | cut -d, -f1)
mean_g=$(echo $means_rgb | cut -d, -f2)
mean_b=$(echo $means_rgb | cut -d, -f3)
mean_alpha=$(convert alpha.png -format "%[fx:mean]" info:)
mean_r=$(convert xc: -format "%[fx:255*$mean_r/$mean_alpha]" info:)
mean_g=$(convert xc: -format "%[fx:255*$mean_g/$mean_alpha]" info:)
mean_b=$(convert xc: -format "%[fx:255*$mean_b/$mean_alpha]" info:)
echo "$mean_r, $mean_g, $mean_b"
100.203, 81.4768, 98.6362
To get the min and max, taking the cue from Mark Setchell's idea:
convert logot.png -background black -alpha background -alpha off -format "%[fx:255*maxima.r], %[fx:255*maxima.g], %[fx:255*maxima.b]n" info:
255, 250, 244
convert logot.png -background white -alpha background -alpha off -format "%[fx:255*minima.r], %[fx:255*minima.g], %[fx:255*minima.b]n" info:
4, 0, 0
answered Nov 19 '18 at 19:50
fmw42fmw42
7,47341427
Yeah but unfortunately the-scale 1x1!trick doesn't work for minimum.
– GavinBrelstaff
Nov 19 '18 at 19:56
I have modified my answer to include computing the max and min values using a modification of the suggestion from Mark Setchell.
– fmw42
Nov 19 '18 at 23:44
add a comment |
In ImageMagick, the -scale 1x1! function can be used to compute the mean without including alpha so that you get the mean of only opaque values. So you could do the following:
Create test transparent image:
convert logo: -transparent white logot.png
Compute mean values:
convert logot.png -scale 1x1! -alpha off -format "%[fx:255*u.r], %[fx:255*u.g], %[fx:255*u.b]" info:
100.202, 81.4747, 98.6342
Alternately, you can use the alpha channel as a mask to get the means. You compute the mean of each channel without the alpha channel and the background under the alpha set to black. Then compute the mean of the alpha channel. Then divide each channel mean by the mean of the alpha channel.
convert logo: -transparent white logot.png
convert logot.png -alpha extract alpha.png
means_rgb=$(convert logot.png -background black -alpha background -alpha off -format "%[fx:mean.r],%[fx:mean.g],%[fx:mean.b]" info:)
mean_r=$(echo $means_rgb | cut -d, -f1)
mean_g=$(echo $means_rgb | cut -d, -f2)
mean_b=$(echo $means_rgb | cut -d, -f3)
mean_alpha=$(convert alpha.png -format "%[fx:mean]" info:)
mean_r=$(convert xc: -format "%[fx:255*$mean_r/$mean_alpha]" info:)
mean_g=$(convert xc: -format "%[fx:255*$mean_g/$mean_alpha]" info:)
mean_b=$(convert xc: -format "%[fx:255*$mean_b/$mean_alpha]" info:)
echo "$mean_r, $mean_g, $mean_b"
100.203, 81.4768, 98.6362
To get the min and max, taking the cue from Mark Setchell's idea:
convert logot.png -background black -alpha background -alpha off -format "%[fx:255*maxima.r], %[fx:255*maxima.g], %[fx:255*maxima.b]n" info:
255, 250, 244
convert logot.png -background white -alpha background -alpha off -format "%[fx:255*minima.r], %[fx:255*minima.g], %[fx:255*minima.b]n" info:
4, 0, 0
answered Nov 19 '18 at 19:50
fmw42fmw42
7,47341427
Yeah but unfortunately the-scale 1x1!trick doesn't work for minimum.
– GavinBrelstaff
Nov 19 '18 at 19:56
I have modified my answer to include computing the max and min values using a modification of the suggestion from Mark Setchell.
– fmw42
Nov 19 '18 at 23:44
add a comment |
In ImageMagick, the -scale 1x1! function can be used to compute the mean without including alpha so that you get the mean of only opaque values. So you could do the following:
Create test transparent image:
convert logo: -transparent white logot.png
Compute mean values:
convert logot.png -scale 1x1! -alpha off -format "%[fx:255*u.r], %[fx:255*u.g], %[fx:255*u.b]" info:
100.202, 81.4747, 98.6342
Alternately, you can use the alpha channel as a mask to get the means. You compute the mean of each channel without the alpha channel and the background under the alpha set to black. Then compute the mean of the alpha channel. Then divide each channel mean by the mean of the alpha channel.
convert logo: -transparent white logot.png
convert logot.png -alpha extract alpha.png
means_rgb=$(convert logot.png -background black -alpha background -alpha off -format "%[fx:mean.r],%[fx:mean.g],%[fx:mean.b]" info:)
mean_r=$(echo $means_rgb | cut -d, -f1)
mean_g=$(echo $means_rgb | cut -d, -f2)
mean_b=$(echo $means_rgb | cut -d, -f3)
mean_alpha=$(convert alpha.png -format "%[fx:mean]" info:)
mean_r=$(convert xc: -format "%[fx:255*$mean_r/$mean_alpha]" info:)
mean_g=$(convert xc: -format "%[fx:255*$mean_g/$mean_alpha]" info:)
mean_b=$(convert xc: -format "%[fx:255*$mean_b/$mean_alpha]" info:)
echo "$mean_r, $mean_g, $mean_b"
100.203, 81.4768, 98.6362
To get the min and max, taking the cue from Mark Setchell's idea:
convert logot.png -background black -alpha background -alpha off -format "%[fx:255*maxima.r], %[fx:255*maxima.g], %[fx:255*maxima.b]n" info:
255, 250, 244
convert logot.png -background white -alpha background -alpha off -format "%[fx:255*minima.r], %[fx:255*minima.g], %[fx:255*minima.b]n" info:
4, 0, 0
answered Nov 19 '18 at 19:50
fmw42fmw42
7,47341427
In ImageMagick, the -scale 1x1! function can be used to compute the mean without including alpha so that you get the mean of only opaque values. So you could do the following:
Create test transparent image:
convert logo: -transparent white logot.png
Compute mean values:
convert logot.png -scale 1x1! -alpha off -format "%[fx:255*u.r], %[fx:255*u.g], %[fx:255*u.b]" info:
100.202, 81.4747, 98.6342
Alternately, you can use the alpha channel as a mask to get the means. You compute the mean of each channel without the alpha channel and the background under the alpha set to black. Then compute the mean of the alpha channel. Then divide each channel mean by the mean of the alpha channel.
convert logo: -transparent white logot.png
convert logot.png -alpha extract alpha.png
means_rgb=$(convert logot.png -background black -alpha background -alpha off -format "%[fx:mean.r],%[fx:mean.g],%[fx:mean.b]" info:)
mean_r=$(echo $means_rgb | cut -d, -f1)
mean_g=$(echo $means_rgb | cut -d, -f2)
mean_b=$(echo $means_rgb | cut -d, -f3)
mean_alpha=$(convert alpha.png -format "%[fx:mean]" info:)
mean_r=$(convert xc: -format "%[fx:255*$mean_r/$mean_alpha]" info:)
mean_g=$(convert xc: -format "%[fx:255*$mean_g/$mean_alpha]" info:)
mean_b=$(convert xc: -format "%[fx:255*$mean_b/$mean_alpha]" info:)
echo "$mean_r, $mean_g, $mean_b"
100.203, 81.4768, 98.6362
To get the min and max, taking the cue from Mark Setchell's idea:
convert logot.png -background black -alpha background -alpha off -format "%[fx:255*maxima.r], %[fx:255*maxima.g], %[fx:255*maxima.b]n" info:
255, 250, 244
convert logot.png -background white -alpha background -alpha off -format "%[fx:255*minima.r], %[fx:255*minima.g], %[fx:255*minima.b]n" info:
4, 0, 0
answered Nov 19 '18 at 19:50
fmw42fmw42
7,47341427
edited Nov 20 '18 at 1:23
answered Nov 19 '18 at 19:50
fmw42fmw42
7,47341427
answered Nov 19 '18 at 19:50
fmw42fmw42
7,47341427
answered Nov 19 '18 at 19:50
fmw42fmw42
7,47341427
7,47341427
Yeah but unfortunately the-scale 1x1!trick doesn't work for minimum.
– GavinBrelstaff
Nov 19 '18 at 19:56
I have modified my answer to include computing the max and min values using a modification of the suggestion from Mark Setchell.
– fmw42
Nov 19 '18 at 23:44
add a comment |
Yeah but unfortunately the-scale 1x1!trick doesn't work for minimum.
– GavinBrelstaff
Nov 19 '18 at 19:56
I have modified my answer to include computing the max and min values using a modification of the suggestion from Mark Setchell.
– fmw42
Nov 19 '18 at 23:44
Yeah but unfortunately the
-scale 1x1! trick doesn't work for minimum.– GavinBrelstaff
Nov 19 '18 at 19:56
Yeah but unfortunately the
-scale 1x1! trick doesn't work for minimum.– GavinBrelstaff
Nov 19 '18 at 19:56
I have modified my answer to include computing the max and min values using a modification of the suggestion from Mark Setchell.
– fmw42
Nov 19 '18 at 23:44
I have modified my answer to include computing the max and min values using a modification of the suggestion from Mark Setchell.
– fmw42
Nov 19 '18 at 23:44
add a comment |
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I'm not at a computer, but you know how to count the on and off alpha pixels, yes? And if you multiply the RGB channels by the alpha channel all transparent pixels will go to black so you can find the max. And if you multiply by (255-alpha) you can find the min.
– Mark Setchell
Nov 19 '18 at 21:25
1
Good idea, Mark!
– fmw42
Nov 19 '18 at 23:35
thanks also to Mark!
– GavinBrelstaff
Nov 20 '18 at 17:16