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Topic: how many colors in an image? (Read 431 times) |
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lunetta
 
 
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how many colors in an image?
« on: Dec 17th, 2004, 11:16am » |
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Hello all
I need some suggestion, advice or idea:
I need to develop a piece of code that with the input of a image, it outputs an object array, each object having 2 properties: a unique color value, and its incidence.
So, my main challenge so far is: How can I count how many unique colors I have in an image?
I'm really grateful for any light in the shadow void of algorithms and data structures inside lunetta's mind.
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| « Last Edit: Dec 17th, 2004, 11:32am by lunetta » |
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toxi
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Re: how many colors in an image?
« Reply #2 on: Dec 17th, 2004, 3:19pm » |
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here's one i made earlier/ages ago... should do pretty muc what you want. an Hashtable is an easy-to-use data structure for those type of problems:
Code:BImage img;
Hashtable uniqueCols;
void setup() {
size(200,200);
img=loadImage("logo.gif");
// find & count occurance of unique colours
uniqueCols=countUniqueColours(img);
// get all colour names (RGB hexvalue)
Enumeration colNames=uniqueCols.keys();
// compute contribution for each colour
while(colNames.hasMoreElements()) {
String currCol=(String)colNames.nextElement();
int currColCount=((IntCounter)uniqueCols.get(currCol)).getValue();
// display result
print(currCol+": ");
print(nf(currColCount*100.0/img.pixels.length,1,1));
println("% ("+currColCount+" pixels)");
}
//display image
image(img,0,0);
}
public Hashtable countUniqueColours(BImage img) {
Hashtable index=new Hashtable();
for(int i=0; i<img.pixels.length; i++) {
// use hex value of colour as hash code (unique ID)
String col=Integer.toHexString(img.pixels[i]&0xffffff);
if (!index.containsKey(col)) {
// create new entry, if new colour
index.put(col,new IntCounter(1));
} else {
// or increase count for existing colour
IntCounter counter=(IntCounter)index.get(col);
counter.increment();
}
}
return index;
}
// counter/helper class
// used by countUniqueColours() method
class IntCounter {
int value;
IntCounter(int i) {
value=i;
}
void increment() {
value++;
}
int getValue() {
return value;
}
} |
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| « Last Edit: Dec 17th, 2004, 3:23pm by toxi » |
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http://toxi.co.uk/
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lunetta
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Re: how many colors in an image?
« Reply #3 on: Dec 17th, 2004, 6:16pm » |
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thanks, I'll study both programs.
I coded a counter last night, and 8 hours laters processing was still counting a 50x50 pixels image. That's slooooooooooow (It worked for a 10x10). So I guess my approach wasn't very good. Imagine a 1280x1024...
thanks again for the feedback
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