Possible bug/limitation of fx string formats

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fmw42
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Location: Sunnyvale, California, USA

Possible bug/limitation of fx string formats

Post by fmw42 » 2017-09-12T18:25:14-07:00

IM 7.0.7.1 Q16 HDRI Mac OSX Sierra.

If I do the following I think I get correct results.

Code: Select all

magick -size 64x64 gradient:            -blur 1x1 -define quantum:format=floating-point -depth 64 gradient_u.tif
magick -size 64x64 gradient: -rotate 90 -blur 1x1 -define quantum:format=floating-point -depth 64 gradient_v.tif
magick gradient_u.tif gradient_v.tif -fx 'u/v' -define quantum:format=floating-point -depth 64 divide.tif
magick identify -verbose -precision 15 divide.tif
min: 291.016 (0.00444061)
max: 1.47581e+07 (225.194)
mean: 268324 (4.09437)


However, -precision does not affect the min, max, mean verbose information.



More importantly, fx string formats do not seem to give the same answers. Perhaps there is clamping?

Code: Select all

magick -size 64x64 gradient:            -blur 1x1 -define quantum:format=floating-point -depth 64 gradient_u.tif
magick -size 64x64 gradient: -rotate 90 -blur 1x1 -define quantum:format=floating-point -depth 64 gradient_v.tif
magick gradient_u.tif gradient_v.tif -fx 'u/v' -precision 15 -format "min=%[fx:min]\n max=%[fx:max]\n mean=%[fx:mean] \n" info:
min=0
max=0
mean=4.09436179140917




But non-fx string format seem correct.

Code: Select all

magick -size 64x64 gradient:            -blur 1x1 -define quantum:format=floating-point -depth 64 gradient_u.tif
magick -size 64x64 gradient: -rotate 90 -blur 1x1 -define quantum:format=floating-point -depth 64 gradient_v.tif
magick gradient_u.tif gradient_v.tif -fx 'u/v' -precision 15 -format "min=%[min]\n max=%[max]\n mean=%[mean]\n" info:
min=291.015655517578
max=14758093
mean=268324.489530727

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magick
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Re: Possible bug/limitation of fx string formats

Post by magick » 2017-09-13T06:26:16-07:00

Fixed the precision problem. And here is the command you want to use to get expected results:

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magick gradient_u.tif gradient_v.tif -fx 'u/v' -precision 15 -format "minima=%[fx:minima]\n maxima=%[fx:maxima]\n mean=%[fx:mean] \n" info:
Max() and min() are functions, see https://www.imagemagick.org/script/fx.php.

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fmw42
Posts: 22105
Joined: 2007-07-02T17:14:51-07:00
Location: Sunnyvale, California, USA

Re: Possible bug/limitation of fx string formats

Post by fmw42 » 2017-09-13T08:53:40-07:00

magick wrote:
2017-09-13T06:26:16-07:00
Fixed the precision problem. And here is the command you want to use to get expected results:

Code: Select all

magick gradient_u.tif gradient_v.tif -fx 'u/v' -precision 15 -format "minima=%[fx:minima]\n maxima=%[fx:maxima]\n mean=%[fx:mean] \n" info:
Max() and min() are functions, see https://www.imagemagick.org/script/fx.php.
Thanks. I keep forgetting that fx uses different forms of min and max (minima and maxima). Sorry for the false alarm.

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