"The problem was that I wasn't accounting for alpha. So a palette from an image that uses alpha would have accidental duplicate records."
I figured this out after finding this Convert RGBA color to RGB
質問
The project in question: https://github.com/matutter/Pixel2 is a personal project to replace some out of date software at work. What it should do is, the user adds an image and it generates a color palette of the image. The color palette should have no duplicate colors. (thats the only important stuff)
My question is: why do larger or hi-res or complex images not work as well? (loss of color data)
Using dropzone.js I have the user put a picture on the page. The picture is a thumbnail. Next I use jquery to find the src out of a <img src="...">
. I pass that src to a function that does this
function generate(imgdata) {
var imageObj = new Image();
imageObj.src = imgdata;
convert(imageObj); //the function that traverses the image data pulling out RGB
}
the "convert" function pulls out the data fairly simply by
for(var i=0, n=data.length; i<n; i+=4, pixel++ ) {
r = data[i];
g = data[i+1];
b = data[i+2];
color = r + g + b; // format is a string of **r, g, b**
}
finally, the last part of the main algorithme filters out duplicate colors, I only want just 1 occurrence of each... here's the last part
color = monoFilter(color); // the call
function monoFilter(s) {
var unique = [];
$.each(s, function(i, el){
if($.inArray(el, unique) === -1) unique.push(el);
});
unique.splice(0,1); //remove undefine
unique.unshift("0, 0, 0"); //make sure i have black
unique.push("255, 255, 255"); //and white
return unique;
}
I'm hoping someone can help me identify why there is such a loss of color data in big files.
If anyone is actually interesting enough to look at the github, the relivent files are js/pixel2.js, js/dropzone.js, and ../index.html
解決 2
"The problem was that I wasn't accounting for alpha. So a palette from an image that uses alpha would have accidental duplicate records."
I figured this out after finding this Convert RGBA color to RGB
他のヒント
This is probably the cause of the problem:
color = r + g + b; // format is a string of **r, g, b**
This simply adds the numbers together and the more pixels you have the higher risk you run to get the same number. For example, these colors generate the same result:
R G B
color = 90 + 0 + 0 = 90;
color = 0 + 90 + 0 = 90;
color = 0 + 0 + 90 = 90;
even though they are completely different colors.
To avoid this you can do it like this if you want a string:
color = [r,g,b].join();
or you can create an integer value of them (which is faster to compare with than a string):
color = (b << 16) + (g << 8) + r; /// LSB byte-order
Even an Euclidean vector would be better:
color = r*r + g*g + b*b;
but with the latter you risk eventually the same scenario as the initial one (but useful for nearest color scenarios).
Anyways, hope this helps.