Memory efficient conversion of cmyk jpeg to rgb jpeg

Question

I'm looking for a memory efficient way to convert a jpeg image from cmyk to rgb.
I can't load the whole image in memory. The image is too big (I already have a lot of ram).
Do you know how to do it? Would you share it with us?
At the end of this thread (http://forum.java.sun.com/thread.jspa?messageID=9625078) I show how to do it when loading the whole image in memory. But that's not what I'm looking for. May be you can find a better way to achieve a similar output.

Answer 1

Can you show me how it would look like? 1. SInce CMYK is 4 bytes per pixel the byte array size is w*h*4 which is bigger than w*h*3, so there is no problem to use the same array.
As you can see from this line:raster = Raster.createInterleavedRaster(new DataBufferByte(rgb, rgb.length), w, h, w * 3, 3, new int[]{0, 1, 2}, null);You are passing the size of the array to the DataBufferByte constructor and also to the createInterleavedRaster, so you can use an array with bigger size and just pass w*h*3 instread of rbg.length to DataBufferByte constructor.
2. You can acces the buffer directly instead of using raster.getSamples which creates a new array and places the values in it:
Instead of this:
int c = 255 - C;
int m = 255 - M[i];
int y = 255 - Y[i];
int k = 255 - K[i];
Do this:
int c = 255 - data[i*4];
int m = 255 - data[i*4+1];
int y = 255 - data[i*4+2];
int k = 255 - data[i*4+3];