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How to extract Photoshop curve points to RGB number array?

Hi I made some filter effects using Photoshop curves and they look like this:
enter image description here

enter image description here

Is there a way I can extract each one of the 256 numbers from each color so it is a number array like this?

var r = [0, 0, 0, 1, 1, 2, 3, 3, 3, 4, 4, 4, 5, 5, 5, 6, 6, 7, 7, 7, 7, 8, 8, 8, 9, 9, 9, 9, 10, 10, 10, 10, 11, 11, 12, 12, 12, 12, 13, 13, 13, 14, 14, 15, 15, 16, 16, 17, 17, 17, 18, 19, 19, 20, 21, 22, 22, 23, 24, 25, 26, 27, 28, 29, 30, 31, 32, 33, 34, 35, 36, 37, 39, 40, 41, 42, 44, 45, 47, 48, 49, 52, 54, 55, 57, 59, 60, 62, 65, 67, 69, 70, 72, 74, 77, 79, 81, 83, 86, 88, 90, 92, 94, 97, 99, 101, 103, 107, 109, 111, 112, 116, 118, 120, 124, 126, 127, 129, 133, 135, 136, 140, 142, 143, 145, 149, 150, 152, 155, 157, 159, 162, 163, 165, 167, 170, 171, 173, 176, 177, 178, 180, 183, 184, 185, 188, 189, 190, 192, 194, 195, 196, 198, 200, 201, 202, 203, 204, 206, 207, 208, 209, 211, 212, 213, 214, 215, 216, 218, 219, 219, 220, 221, 222, 223, 224, 225, 226, 227, 227, 228, 229, 229, 230, 231, 232, 232, 233, 234, 234, 235, 236, 236, 237, 238, 238, 239, 239, 240, 241, 241, 242, 242, 243, 244, 244, 245, 245, 245, 246, 247, 247, 248, 248, 249, 249, 249, 250, 251, 251, 252, 252, 252, 253, 254, 254, 254, 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]

Sorry for the question if it’s stupid, i’m not even sure what i’m asking, it’s late.

UPDATE: following Mark Setchell‘s answer, i was able to create a saved.ppm file with these values inside it.

enter image description here

The last step was to extract the RGB values from this long string of numbers, Red is the 0th, 3nd, 6th number, Green is the 1st, 4th, 7th number etc.

For anyone else’s interest, I was trying to create a filter on Photoshop curves, then extract its RGB values and apply it using pixel cross processing on HTML Canvas, similar to a demo shown here.

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2

Answers


  1. 0

    I don’t feel like writing the code today, least of all when you are not too sure what you are up to! However, what you are asking is perfectly achievable.

    If you save the curve you have created (the Save option is in the top right menu), you will get a .ACV file. The format of this file is given here if you scroll down to the section entitled Curves. It is a pretty simple format with just an identifier and a version number then a count of the number of points that you have defined for your curve, i.e. 6 in your case. Then, for each point, the 4 coordinates. These can be pretty easily extracted with Perl or similar.

    You could then fit a curve to those points, probably using GNUplot, and interpolate to find the points you are looking for.

    Excerpt from referenced document:

    enter image description here

    Here is an extract from some code I wrote in Perl that actually writes a .ACV file. I know you will actually want to read one, bit you’ll get the idea of the byte packing technique…

    #!/usr/bin/perl
use strict;
use warnings;
use Image::Magick;
use Data::Dumper;

my $Debug=1;    # 1=print debug messages, 0=don't
my $NPOINTS=5;  # Number of points in curve we create

....
.... other stuff
....

# Work out name of the curve file = image basename + acv
my $curvefile=substr($imagename,0,rindex($imagename,'.')) . ".acv";
open(my $out,'>:raw',$curvefile) or die "Unable to open: $!";
print $out pack("s>",4); # Version=4
print $out pack("s>",4); # Number of curves in file = Master NULL curve + R + G + B

print $out pack("s>",2);                        # Master NULL curve with 2 points for all channels
print $out pack("s>",0  ),pack("s>",0  );       # 0 out, 0 in
print $out pack("s>",255),pack("s>",255);       # 255 out, 255 in

print $out pack("s>",2+$NPOINTS);               # Red curve
print $out pack("s>",0  ),pack("s>",0  );       # 0 out, 0 in
for($p=0;$p<$NPOINTS;$p++){
   print $out pack("s>",$Rpoint[$p]),pack("s>",$greypoint[$p]);
}
print $out pack("s>",255),pack("s>",255);       # 255 out, 255 in

print $out pack("s>",2+$NPOINTS);               # Green curve
print $out pack("s>",0  ),pack("s>",0  );       # 0 out, 0 in
for($p=0;$p<$NPOINTS;$p++){
   print $out pack("s>",$Gpoint[$p]),pack("s>",$greypoint[$p]);
}
print $out pack("s>",255),pack("s>",255);       # 255 out, 255 in

print $out pack("s>",2+$NPOINTS);               # Blue curve
print $out pack("s>",0  ),pack("s>",0  );        # 0 out, 0 in
for($p=0;$p<$NPOINTS;$p++){
   print $out pack("s>",$Bpoint[$p]),pack("s>",$greypoint[$p]);
}
print $out pack("s>",255),pack("s>",255);        # 255 out, 255 in

close($out);
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  2. 0

    Here is a totally different, and simpler way of doing it. Save the data below in a file called ramp.ppm – it is a Portable Pixmap format from the NetPBM suite see Wikipedia here. It is a black-to-white greyscale ramp 256 pixels wide and 1 pixel tall.

    Load that into Photoshop and apply your curve to it then save as a PNG file.

    P3
256 1
255
0 0 0
1 1 1
2 2 2
3 3 3
4 4 4
5 5 5
6 6 6
7 7 7
8 8 8
9 9 9
10 10 10
11 11 11
12 12 12
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255 255 255

    If you have Linux, and you have ImageMagick, you can then convert the saved PNG file back into a PPM file with

    convert saved.png -compress none saved.ppm

    The file saved.ppm will then show you the output of your curve for each input value in the greyscale ramp – in effect it will be the 256 values you are looking for.

    If you don’t have ImageMagick, just give me the PNG file and I’ll convert it for you.

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