macOS 16-bit to 8-bit image conversion

[madart9]

I'm trying to make a scientific program that works with 16-bit tiff directories (of images) but displays the images as 8-bit. I also want to allow for the adjusting of the white and black levels. As of now, I'm reading in the 16-bit tiff, getting out the data, editing it, and then loading it into a new image. However, I can't figure out how to set the IKImageView settings correctly. It displays my 16-bit tiff as two (almost) duplicate versions in the top left quadrant and top right quadrant with black in the bottom quadrants. I suspect this is a problem with the number of bytes per row and bits per component in my ikimageview output, but I can't figure out how to edit the NSDictionary metadata.

		if ([[(NSDictionary *)imageProperties valueForKey:(NSString *)kCGImagePropertyDepth] intValue] == 16) {
			CGImageRef imR = CGImageSourceCreateImageAtIndex(imageSource, index, NULL);
			CFDataRef pixData = CGDataProviderCopyData(CGImageGetDataProvider(imR));
			UInt16 * pixels = (UInt16 *) CFDataGetBytePtr(pixData);
			UInt8 * eightPix = (UInt8 *) CFDataGetBytePtr(pixData);
			int plen = CFDataGetLength(pixData);
			int i;
			for (i = 0; i < heightInPixels*widthInPixels; i++) {
				eightPix[i] = (UInt8) pixels[i];
			}
			CGContextRef imcont = CGBitmapContextCreate(pixels, CGImageGetWidth(imR), CGImageGetHeight(imR), CGImageGetBitsPerComponent(imR), CGImageGetBytesPerRow(imR), CGImageGetColorSpace(imR), CGImageGetBitmapInfo(imR));
						CGImageRef outR = CGBitmapContextCreateImage(imcont);
			
			CFMutableDictionaryRef outProperties = CFDictionaryCreateMutableCopy(NULL, 0, imageProperties);
//			const UInt8 * outVal;
//			outVal = 8;
//			NSString * outVal = (NSString *) 8;
//			CFDictionarySetValue(outProperties, kCGImagePropertyDepth, outVal);
//			outVal = (NSString *) CGImageGetWidth(imR);
//			CFDictionarySetValue(outProperties, kCGImagePropertyDepth, outVal);
			[imageView setImage: outR imageProperties: (NSDictionary *)outProperties];

 

[Muncher]

I don't know about what you're doing (over my head ). The simplest way I can think of to load and convert images is through SDL/SDL_image. Load the image using Load_IMG() into an SDL surface, then convert it to the format you want. There are tutorials around the interwebs for converting an SDL_surface into something OpenGL can read, for instance.

 

[autorelease]

Use CGContextDrawImage() to draw your 16-bit-per-channel image into an 8-bit-per-channel CGBitmapContext. It should handle the conversion automatically.

Core Image might help as well.

Don't go mucking about with SDL. The functionality you need is in the OS.

 

[Sander]

Wait, your "pixels" and "eightPix" are pointing to the same memory - you are trying to convert the image data in-place. That won't work. Also, converting 16-bit images to 8-bit images can't be done with a simple cast for each pixel. Instead, you divide each 16-bit pixel value by 257. (Someone will try to correct me here and say it should be 256, but it's not a typo.)

But perhaps you don't really need to do this conversion at all (like autorelease said), since I believe you can display 16-bit TIFF images just fine on MacOS X. Why exactly do you want to convert it to 8-bit yourself?