Problems with Image Statistics (fx:maxima etc.)
Posted: 2017-02-09T04:35:35-07:00
I'm running on IM 7.0.2-4 Q16 x86_64, using PerlMagick and getting some strange numbers from the fx:mean, fx:maxima, functions. These (I suspect) may be issues with the main IM program (rather than Perl Magick).
I'm also getting some strange numbers from the Perl Magick Statistics() method.
To illustrate (in Perl Magick - since I don't use the command line)
The (rather clumsy) code below generates a 3 pixel image including alpha channel and assigns different values to each pixel.
The Identify - verbose output is as follows
This appears to give all the correct statistical data.
The output from the various fx:maxima, minima and mean functions are as follows:
This is giving erroneous results for some of the returns.
This appears to miss out the r channel, but gives correct values for the g,b,& a channels (albeit in the wrong place in the array)
Any chance you could take a look at these issues?
Regards
Mike
I'm also getting some strange numbers from the Perl Magick Statistics() method.
To illustrate (in Perl Magick - since I don't use the command line)
The (rather clumsy) code below generates a 3 pixel image including alpha channel and assigns different values to each pixel.
Code: Select all
my $image = Image::Magick->new;
my @pixel;
$image->Set(size=>'3x1');
$image->Read('canvas:black');
$image->Color(color=>'blue');
$image->Set(alpha=>'On');
$image->SetPixel(x=>0, y=>0, color=>[1,1,0.75,1]);
$image->SetPixel(x=>1, y=>0, color=>[1,0,0.5,0.2]);
$image->SetPixel(x=>2, y=>0, color=>[0,0,0.25,1]);
$image->Identify();
print "Mean r = ".$image->Get('%[fx:mean.r]')."\n";
print "Mean g = ".$image->Get('%[fx:mean.g]')."\n";
print "Mean b = ".$image->Get('%[fx:mean.b]')."\n";
print "Mean = ".$image->Get('%[fx:mean]')."\n";
print "Mean a = ".$image->Get('%[fx:mean.a]')."\n";
print "Mean o = ".$image->Get('%[fx:mean.o]')."\n\n";
print "Maxima r = ".$image->Get('%[fx:maxima.r]')."\n";
print "Maxima g = ".$image->Get('%[fx:maxima.g]')."\n";
print "Maxima b = ".$image->Get('%[fx:maxima.b]')."\n";
print "Maxima = ".$image->Get('%[fx:maxima]')."\n";
print "Max = ".$image->Get('%[fx:max]')."\n";
print "Maxima a = ".$image->Get('%[fx:maxima.a]')."\n";
print "Maxima o = ".$image->Get('%[fx:maxima.o]')."\n\n";
print "Minima r = ".$image->Get('%[fx:minima.r]')."\n";
print "Minima g = ".$image->Get('%[fx:minima.g]')."\n";
print "Minima b = ".$image->Get('%[fx:minima.b]')."\n";
print "Minima = ".$image->Get('%[fx:minima]')."\n";
print "Min = ".$image->Get('%[fx:min]')."\n";
print "Minima a = ".$image->Get('%[fx:minima.a]')."\n";
print "Minima o = ".$image->Get('%[fx:minima.o]')."\n\n";
my @stats = $image->Statistics();
my ($i, $j);
for ($i=0; $i<4; $i++) {
for ($j=0; $j<8; $j++) {
print $stats[$i*8+$j]."/";
}
print "\n";
}
Code: Select all
Image: black
Base filename: black
Format: CANVAS (Constant image uniform color)
Class: DirectClass
Geometry: 3x1+0+0
Units: Undefined
Type: PaletteAlpha
Base type: TrueColorAlpha
Endianess: LSB
Colorspace: sRGB
Depth: 8/16-bit
Channel depth:
Red: 1-bit
Green: 1-bit
Blue: 16-bit
Alpha: 4-bit
Channel statistics:
Pixels: 3
Red:
min: 0 (0)
max: 255 (1)
mean: 170 (0.666667)
standard deviation: 120.208 (0.471405)
kurtosis: -1.5
skewness: -0.707107
entropy: 0.918296
Green:
min: 0 (0)
max: 255 (1)
mean: 85 (0.333333)
standard deviation: 120.208 (0.471405)
kurtosis: -1.5
skewness: 0.707107
entropy: 0.918296
Blue:
min: 63.75 (0.25)
max: 191.25 (0.75)
mean: 127.5 (0.5)
standard deviation: 52.0517 (0.204124)
kurtosis: -1.5
skewness: 0
entropy: 1
Alpha:
min: 51 (0.2)
max: 255 (1)
mean: 187 (0.733333)
standard deviation: 96.1665 (0.377124)
kurtosis: -1.5
skewness: -0.707107
entropy: -nan
Image statistics:
Overall:
min: 0 (0)
max: 255 (1)
mean: 142.375 (0.558333)
standard deviation: 101.066 (0.396337)
kurtosis: -1.28206
skewness: -0.213977
entropy: 0.709148
Colors: 3
Histogram:
1: ( 0, 0, 64,255) #000040FF srgba(0,0,64,1)
1: (255, 0,128, 51) #FF008033 srgba(255,0,128,0.2)
1: (255,255,191,255) #FFFFBFFF srgba(255,255,191,1)
Rendering intent: Perceptual
Gamma: 0.454545
Chromaticity:
red primary: (0.64,0.33)
green primary: (0.3,0.6)
blue primary: (0.15,0.06)
white point: (0.3127,0.329)
Tile geometry: 3x1+0+0
Alpha color: grey74
Background color: white
Border color: srgb(223,223,223)
Transparent color: none
Interlace: None
Intensity: Undefined
Compose: Over
Page geometry: 3x1+0+0
Dispose: Undefined
Iterations: 0
Compression: Undefined
Orientation: Undefined
Properties:
date:create: 2017-02-09T11:00:47+00:00
date:modify: 2017-02-09T11:00:47+00:00
signature: 2721d18926bbdf0ebf14e8943047e4232109e609a135f0b82fdd882059921cc9
Tainted: True
Filesize: 0B
Number pixels: 3
Pixels per second: 3PB
User time: 0.000u
Elapsed time: 0:01.000
Version: ImageMagick 7.0.2-4 Q16 x86_64 2016-12-05 http://www.imagemagick.org
This appears to give all the correct statistical data.
The output from the various fx:maxima, minima and mean functions are as follows:
Code: Select all
Mean r = 0.666667
Mean g = 0.333333
Mean b = 0.5
Mean = 0.5
Mean a = 0
Mean o = 0
Maxima r = 1
Maxima g = 1
Maxima b = 0.749999
Maxima = 0.749999
Max = 0
Maxima a = 1
Maxima o = 1
Minima r = 0
Minima g = 0
Minima b = 0.250001
Minima = 0.250001
Min = 0
Minima a = 0.2
Minima o = 0.2
- fx:mean gives and incorrect value. It appears to actually give the value from fx:maxima.b
fx:mean.a and fx:mean.o give incorrect values. Interestingly if the fx:mean call (just before the fx:mean.a call) is omitted the value of fx:mean.a changes (but is still incorrect) !
fx:Maxima gives an incorrect value, again apearing to give the fx:maxima.b value.
fx:Minima - as above.
fx:Max & fx:Min give no values (and I didn't expect then to)
All others appear to function as expected.
Code: Select all
1/0/1/0.333333333333333/0.471404520791032/-1.5/0.707106781186548/0.91829583405449/
16/0.25/0.75/0.5/0.204124145231932/-1.50000000000001/0/1/
4/0.2/1/0.733333333333333/0.377123616632825/-1.50000000000001/-0.707106781186548/-nan/
1/2.74310389084049e+303/-2.74310389084049e+303/0/0/0/0/-nan/
Any chance you could take a look at these issues?
Regards
Mike
