Question

I am trying to convert an NSImage to a CIImage. When I do this, there seems to be a huge loss in image quality. I think it is because of the “TIFFRepresentation”. Does anyone have a better method? Thanks a lot.

NSImage *image = [[NSImage alloc] initWithData:[someSource dataRepresentation]];

NSData  * tiffData = [image TIFFRepresentation];
CIImage *backgroundCIImage = [[CIImage alloc] initWithData:tiffData];

CIContext *ciContext = [[NSGraphicsContext currentContext] CIContext];  
[ciContext drawImage:backgroundCIImage atPoint:CGPointZero fromRect:someRect];

Answer 1

I finally solved the problem. Basically, I render the pdf document two times its normal resolution offscreen and then capture the image displayed by the view. For a more detailed image, just increase the scaling factor. Please see the code below for the proof of concept. I didn’t show the CIImage but once you get the bitmap, just use the CIImage method to create the CIImage from the bitmap.

    NSImage *pdfImage = [[NSImage alloc] initWithData:[[aPDFView activePage] dataRepresentation]];
    NSSize size = [pdfImage size];
    NSRect imageRect = NSMakeRect(0, 0, size.width, size.height);
    imageRect.size.width *= 2; //Twice the scale factor
    imageRect.size.height *= 2; //Twice the scale factor

    PDFDocument *pageDocument = [[[PDFDocument alloc] init] autorelease];
    [pageDocument insertPage:[aPDFView activePage] atIndex:0];

    PDFView *pageView = [[[PDFView alloc] init] autorelease];
    [pageView setDocument:pageDocument];
    [pageView setAutoScales:YES];

    NSWindow *offscreenWindow = [[NSWindow alloc] initWithContentRect:imageRect 
                                                            styleMask:NSBorderlessWindowMask
                                                              backing:NSBackingStoreRetained
                                                                defer:NO];

    [offscreenWindow setContentView:pageView];
    [offscreenWindow display];
    [[offscreenWindow contentView] display]; // Draw to the backing buffer

    // Create the NSBitmapImageRep
    [[offscreenWindow contentView] lockFocus];

    NSBitmapImageRep* rep = [[NSBitmapImageRep alloc] initWithFocusedViewRect:imageRect];

    // Clean up and delete the window, which is no longer needed.
    [[offscreenWindow contentView] unlockFocus];

    [compositeImage TIFFRepresentation]];
    NSData *imageData = [rep representationUsingType: NSJPEGFileType properties: nil];
    [imageData writeToFile:@"/Users/David/Desktop/out.jpg" atomically: YES];

    [offscreenWindow release];