[kupan787]

I am looking for a routine to convert a rgb tiff into a greyscale tiff. I am currently using the following, but it takes about 4-5 seconds on a US letter sized page (too slow!). I had thought to use tiff2bw (part of the libtiff tools), but I get an error when using an image that I saved out using TIFFRepresentation (about bad samplesPerPixel)

Any help would be greatly appriciated.

Code:
- (NSImage *)filterImage:(NSImage *)srcImage
{
    NSBitmapImageRep *TIFFRep = [NSBitmapImageRep imageRepWithData:[srcImage TIFFRepresentation]];
    
    int samplesPerPixel = [TIFFRep samplesPerPixel];
    int bytesPerSample = ([TIFFRep bitsPerPixel]/8)/samplesPerPixel;
    int totalBytes = [TIFFRep pixelsHigh]*[TIFFRep pixelsWide]*samplesPerPixel*bytesPerSample;
    
    grayRep = [[NSBitmapImageRep alloc] initWithBitmapDataPlanes:NULL
                                                pixelsWide:[TIFFRep pixelsWide]
                                                pixelsHigh:[TIFFRep pixelsHigh]
                                             bitsPerSample:8
                                           samplesPerPixel:1
                                                  hasAlpha:NO
                                                  isPlanar:NO
                                            colorSpaceName:NSCalibratedWhiteColorSpace
                                               bytesPerRow:0
                                              bitsPerPixel:0];
                                                                                      
    [grayRep setSize:[TIFFRep size]];
    
    unsigned char 	*TIFFBitmapPointer = [TIFFRep bitmapData];
    unsigned char	*grayBitmapPointer = [grayRep bitmapData];

    if((bytesPerSample==1)&&(samplesPerPixel>2))
    {
        int o = 0;
        int i = 0;
        int background = 255;
        
        for (i=0; i<totalBytes; i+=samplesPerPixel)
        {
            int R = (int)*(TIFFBitmapPointer+i);
            int G = (int)*(TIFFBitmapPointer+i+1);
            int B = (int)*(TIFFBitmapPointer+i+2);

            int grayValue = (int)((R+G+B)/3);

            if (samplesPerPixel==4)
            {
                int alpha = (int)*(TIFFBitmapPointer+i+3);  // this is the alpha value

                grayValue = (int) (    (grayValue*alpha + background*(255-alpha))    / 255);
            }

            *(grayBitmapPointer+o) = grayValue;
            o++;
        }
            
    } else NSLog(@"Bytes per sample != 1 or less than 3 samples per pixel");;
    
    [grayRep setSize:originalSize];
    NSImage *grayImage = [[NSImage alloc] initWithData:[grayRep TIFFRepresentation]];
    
    return grayImage;
}