I have a litho image (black & white pixels only) and I want to make all the
white pixels transparent. I am using Quartz 2d to display the image and I have
a Quartz composition containing a single .cikernel...
kernel vec4 whiteToTransparent(sampler source_image)
{
vec4 pixValue;
pixValue = sample(source_image, samplerCoord(source_image));
return (pixValue == vec4(1,1,1,1) ? vec4(1,1,1,0) : vec4(pixValue));
}
....it doesn't seem to work. Here is what I have...
- (void)drawRect:(NSRect)rect {
CGContextRef context = [[NSGraphicsContext currentContext] graphicsPort];
NSString* imagePath = [[NSBundle mainBundle] pathForResource:@"Richards Thres
1 of 7" ofType:@"tif"];
NSImage *theImage = [[[NSImage alloc]
initByReferencingFile:imagePath]autorelease];
[selfMyDrawTransparencyLayer:context:rect.size.width:rect.size.height:theImage];
}
- (void) MyDrawTransparencyLayer: (CGContextRef)myContext: (float)wd:
(float)ht: (NSImage *)addThisImage//1
{
[selfsetKeyCGImageRef:[selfCGImageRefFromNSImage:addThisImage]];
CGRect rect = CGRectMake(0, 0, CGImageGetWidth(keyCGImageRef),
CGImageGetHeight(keyCGImageRef));
keyCGImageRef = ApplyWhiteToTransparentComposition([@"whiteToTransparent"
UTF8String], keyCGImageRef);
CGContextBeginTransparencyLayer (myContext, NULL);
CGContextDrawImage (myContext, rect, keyCGImageRef);
CGContextEndTransparencyLayer (myContext);
}
- (CGImageRef) CGImageRefFromNSImage:(NSImage*)anImage
{
CFDataRef imgData = (CFDataRef)[anImage TIFFRepresentation];
CGImageSourceRef imageSourceRef = CGImageSourceCreateWithData(imgData, NULL);
return CGImageSourceCreateImageAtIndex(imageSourceRef, 0, NULL);
}
CGImageRef ApplyWhiteToTransparentComposition(const char* compositionName,
const CGImageRef srcImage)
{
CGImageRef resultImage = NULL;
NSAutoreleasePool* pool = [NSAutoreleasePool new];
NSString* compName = [NSString stringWithCString:compositionName];
NSString* compositionPath = [[NSBundle mainBundle] pathForResource:compName
ofType:@"qtz"];
NSOpenGLPixelFormatAttribute attributes[] = {NSOpenGLPFAAccelerated,
NSOpenGLPFANoRecovery, (NSOpenGLPixelFormatAttribute)0};
NSOpenGLPixelFormat* format = [[NSOpenGLPixelFormat alloc]
initWithAttributes:attributes];
NSOpenGLContext* context = [[NSOpenGLContext alloc] initWithFormat:format
shareContext:nil];
@try
{
QCRenderer* renderer = [[QCRenderer alloc] initWithOpenGLContext:context
pixelFormat:format file:compositionPath];
[renderer setValue:(id)srcImage forInputKey:@"source_image"];
[renderer renderAtTime:0.0 arguments:nil];
NSImage* image = [renderer valueForOutputKey:@"output_image"];
if (image)
{
CFDataRef imgData = (CFDataRef)[image TIFFRepresentation];
CGImageSourceRef imageSourceRef = CGImageSourceCreateWithData(imgData, NULL);
resultImage = CGImageSourceCreateImageAtIndex(imageSourceRef, 0, NULL);
}
[renderer release];
}
@catch(id exception)
{
NSLog(@"Error running Quartz Composition '%s': %@", compositionName,
exception);
}
// Done, clean up
[context release];
[format release];
[pool release];
return resultImage;
}
Any ideas?
Thanks
Rick
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