- (CVPixelBufferRef)fastImageFromNSImage:(NSImage *)image
{
    CVPixelBufferRef buffer = NULL;

    
    // config
    size_t width = [image size].width;
    size_t height = [image size].height;
    size_t bitsPerComponent = 8; // *not* CGImageGetBitsPerComponent(image);
    CGColorSpaceRef cs = CGColorSpaceCreateWithName(kCGColorSpaceGenericRGB);
    CGBitmapInfo bi = kCGImageAlphaNoneSkipFirst; // *not* CGImageGetBitmapInfo(image);
    NSDictionary *d = [NSDictionary dictionaryWithObjectsAndKeys:[NSNumber numberWithBool:YES], kCVPixelBufferCGImageCompatibilityKey, [NSNumber numberWithBool:YES], kCVPixelBufferCGBitmapContextCompatibilityKey, nil];
    
    // create pixel buffer
    CVPixelBufferCreate(kCFAllocatorDefault, width, height, k32ARGBPixelFormat, (CFDictionaryRef)d, &buffer);
    CVPixelBufferLockBaseAddress(buffer, 0);
    void *rasterData = CVPixelBufferGetBaseAddress(buffer);
    size_t bytesPerRow = CVPixelBufferGetBytesPerRow(buffer);
    
    // context to draw in, set to pixel buffer's address
    CGContextRef ctxt = CGBitmapContextCreate(rasterData, width, height, bitsPerComponent, bytesPerRow, cs, bi);
    if(ctxt == NULL){
        NSLog(@"could not create context");
        return NULL;
    }
    
    // draw
    NSGraphicsContext *nsctxt = [NSGraphicsContext graphicsContextWithGraphicsPort:ctxt flipped:NO];
    [NSGraphicsContext saveGraphicsState];
    [NSGraphicsContext setCurrentContext:nsctxt];
    [image compositeToPoint:NSMakePoint(0.0, 0.0) operation:NSCompositeCopy];
    [NSGraphicsContext restoreGraphicsState];
    
    CVPixelBufferUnlockBaseAddress(buffer, 0);
    CFRelease(ctxt);
    
    return buffer;
}

http://lists.apple.com/archives/quartz-dev/2006/Oct/msg00096.html

Convert NSImage to CVPixelBufferRef

Objective C