I have some CMYK JPEGs from a PDF which are actually YCCK encoded. I
have read the raster data out using ImageIO so I can then convert to
sRGB.
I am running these through the standard YCC conversion routines, then
adding a CMYK profile and converting to sRGB. Despite using profiles,
I am not getting an exact match.
What am I doing wrong? Is there a better way?
MArkee
/**
* save raw CMYK data by converting to RGB using algorithm
method -
* pdfsages supplied the C source and I have converted -
* This works very well on most colours but not dark shades
which are
* all rolled into black
*
*/
public static BufferedImage iccConvertCMYKImageToRGB(
byte[] buffer,
int w,
int h,boolean debug) {
DeviceCMYKColorSpace cs=new DeviceCMYKColorSpace();
//get cmyk colorspace using Abobe profile
ColorSpace CMYK=cs.getColorSpace();
BufferedImage image = null;
int pixelCount = w * h*4;
double c,m,y,k;
double Y,Cb,Cr,CENTER;
//turn YCCK in Buffer to CYMK using formula
for (int i = 0; i < pixelCount; i = i + 4) {
Y=(buffer[i] & 255);
Cb = (buffer[i+1] & 255)-128;
Cr = (buffer[i+2] & 255)-128;
//CENTER =(buffer[i+3] & 255);
c =( Y +(1.4020d*Cr));
if(c<0d)
c=0d;
if(c>255d)
c=255d;
m =(Y - (0.3441363d*Cb) - (0.71413636d*Cr));
if(m<0d)
m=0d;
if(m>255d)
m=255d;
y =(Y + (1.7718d*Cb));
if(y<0d)
y=0d;
if(y>255d)
y=255d;
buffer[i]=(byte)(255-c);
buffer[i+1]=(byte)(255-m);
buffer[i+2]=(byte)(255-y);
//buffer[i+3]=(byte)(CENTER); //just passed through
}
/**
* create CMYK image from buffer
*/
int[] bands = { 0, 1, 2, 3 };
WritableRaster raster = Raster.createInterleavedRaster(new
DataBufferByte(buffer,buffer.length), w,h,w * 4,4, bands,null);
ColorModel cmykModel = new ComponentColorModel( CMYK, new
int[] { 8, 8, 8, 8 }, false, false, ColorModel.OPAQUE,
DataBuffer.TYPE_BYTE);
image = new BufferedImage(cmykModel, raster, false, null);
/**
* convert to sRGB filtering data via .icm profile (the one
Adobe has in Acrobat)
* Gives exact match on CMYK to sRGB but not YCCK to sRGB
*/
ICC_Profile rgbProfile =
ICC_Profile.getInstance(ColorSpace.CS_sRGB);
rgbCS = new ICC_ColorSpace(rgbProfile);
rgbModel = new ComponentColorModel(rgbCS, new int[] { 8, 8, 8
}, false, false, ColorModel.OPAQUE, DataBuffer.TYPE_BYTE);
WritableRaster rgbRaster
=rgbModel.createCompatibleWritableRaster(w, h);
CSToRGB = new ColorConvertOp(cs.getColorSpace(), rgbCS,
ColorSpaces.hints);
CSToRGB.filter(image.getRaster(), rgbRaster);
//data now sRGB so create image
image =new BufferedImage(w,h,BufferedImage.TYPE_INT_RGB);
image.setData(rgbRaster);
return image;
}
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