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Index › Programming Questions & Help › Programs › Efficient way to 'loop' through pixels
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Efficient way to 'loop' through pixels (Read 728 times)
Alexstre
Efficient way to 'loop' through pixels
Apr 15th, 2008, 11:12pm  
Hello!

I'm trying to keep track of the /popular/ colors in an image by looping through each pixel, checking its HEX value, comparing with what I have found so far and adding it to an array (or incrementing a counter for each color). My problem is that the method I'm using is extremely slow:

PImage c;
c = loadImage("/images/02.jpg");

for (int i = 0; i < c.width*c.height; i += 1)
{
int here = c.pixels[i];
color col = color(red(here), green(here), blue(here));
println(hex(col, 6));
}

Would using get() be faster? or something completely different? Also, is there another way I could use to store the count for each color? (something like Python's dictionaries would be perfect)

Thanks!
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JohnG
Re: Efficient way to 'loop' through pixels
Reply #1 - Apr 15th, 2008, 11:56pm  
You can cut out the "color col=..." line, color is actually a synonym for int.

so your code can be:
Code:
 PImage c;
c = loadImage("/images/02.jpg");
 
for (int i = 0; i < c.width*c.height; i += 1)
{
 println(hex(c.pixels[i];, 6));
}
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Alexstre
Re: Efficient way to 'loop' through pixels
Reply #2 - Apr 16th, 2008, 4:43am  
Quote:
You can cut out the "color col=..." line, color is actually a synonym for int.

so your code can be:
Code:
 PImage c;
c = loadImage("/images/02.jpg");
 
for (int i = 0; i < c.width*c.height; i += 1)
{
 println(hex(c.pixels[i];, 6));
}


Thank you for that! I also decided to check one every five pixels. It won't change the results that much and it is (technically) 5 times faster Smiley
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fry
Re: Efficient way to 'loop' through pixels
Reply #3 - Apr 16th, 2008, 2:47pm  
println() is also very slow--you don't want to use that inside a loop that runs many times.

the best thing to do is compare the actual color value when you want to store it, not its hex value, since the conversion to/from hex (and comparing a hex String) will take a lot of time. just use an array of ints and compare against those.
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