Resize and Save NSImage?

Question

I have an NSImageView which I get an image for from an NSOpenPanel. That works great.

Now, how can I take that NSImage, half its size and save it as the same format in the same directory as the original as well?

If you can help at all with anything I'd appreciate it, thanks.

Answer 1

Check the ImageCrop sample project from Matt Gemmell:
http://mattgemmell.com/source/

Nice example how to resize / crop images.
Finally you can use something like this to save the result (dirty sample):

// Write to TIF
[[resultImg TIFFRepresentation] writeToFile:@"/Users/Anne/Desktop/Result.tif" atomically:YES];

// Write to JPG
NSData *imageData = [resultImg  TIFFRepresentation];
NSBitmapImageRep *imageRep = [NSBitmapImageRep imageRepWithData:imageData];
NSDictionary *imageProps = [NSDictionary dictionaryWithObject:[NSNumber numberWithFloat:0.9] forKey:NSImageCompressionFactor];
imageData = [imageRep representationUsingType:NSJPEGFileType properties:imageProps];
[imageData writeToFile:@"/Users/Anne/Desktop/Result.jpg" atomically:NO];

Answer 2

Since NSImage objects are immutable you will have to:

1. Create a Core Graphics context the size of the new image.
2. Draw the NSImage into the CGContext. It should automatically scale it for you.
3. Create an NSImage from that context
4. Write out the new NSImage
5. Don't forget to release any temporary objects you allocated.

There are definitely other options, but this is the first one that came to mind.

Answer 3

+(NSImage*) resize:(NSImage*)aImage scale:(CGFloat)aScale
{
    NSImageView* kView = [[NSImageView alloc] initWithFrame:NSMakeRect(0, 0, aImage.size.width * aScale, aImage.size.height* aScale)];
    [kView setImageScaling:NSImageScaleProportionallyUpOrDown];
    [kView setImage:aImage];

    NSRect kRect = kView.frame;
    NSBitmapImageRep* kRep = [kView bitmapImageRepForCachingDisplayInRect:kRect];
    [kView cacheDisplayInRect:kRect toBitmapImageRep:kRep];

    NSData* kData = [kRep representationUsingType:NSJPEGFileType properties:nil];
    return [[NSImage alloc] initWithData:kData];
}

Answer 4

Here is a specific implementation

-(NSImage*)resizeImage:(NSImage*)input by:(CGFloat)factor
{    
    NSSize size = NSZeroSize;      
    size.width = input.size.width*factor;
    size.height = input.size.height*factor; 

    NSImage *ret = [[NSImage alloc] initWithSize:size];
    [ret lockFocus];
    NSAffineTransform *transform = [NSAffineTransform transform];
    [transform scaleBy:factor];  
    [transform concat]; 
    [input drawAtPoint:NSZeroPoint fromRect:NSZeroRect operation:NSCompositeCopy fraction:1.0];    
    [ret unlockFocus];        

    return [ret autorelease];
}

Keep in mind that this is pixel based, with HiDPI the scaling must be taken into account, it is simple to obtain :

-(CGFloat)pixelScaling
{
    NSRect pixelBounds = [self convertRectToBacking:self.bounds];
    return pixelBounds.size.width/self.bounds.size.width;
}

Answer 5

Apple has source code for downscaling and saving images found here http://developer.apple.com/library/mac/#samplecode/Reducer/Introduction/Intro.html

Answer 6

Here is some code that makes a more extensive use of Core Graphics than other answers. It's made according to hints in Mark Thalman's answer to this question.

This code downscales an NSImage based on a target image width. It's somewhat nasty, but still useful as an extra sample for documenting how to draw an NSImage in a CGContext, and how to write contents of CGBitmapContext and CGImage into a file.

You may want to add extra error checking. I didn't need it for my use case.

- (void)generateThumbnailForImage:(NSImage*)image atPath:(NSString*)newFilePath forWidth:(int)width
{
    CGSize size = CGSizeMake(width, image.size.height * (float)width / (float)image.size.width);
    CGColorSpaceRef rgbColorspace = CGColorSpaceCreateDeviceRGB();

    CGBitmapInfo bitmapInfo = kCGImageAlphaPremultipliedLast;
    CGContextRef context = CGBitmapContextCreate(NULL, size.width, size.height, 8, size.width * 4, rgbColorspace, bitmapInfo);
    NSGraphicsContext * graphicsContext = [NSGraphicsContext graphicsContextWithGraphicsPort:context flipped:NO];
    [NSGraphicsContext setCurrentContext:graphicsContext];

    [image drawInRect:NSMakeRect(0, 0, size.width, size.height) fromRect:NSMakeRect(0, 0, image.size.width, image.size.height) operation:NSCompositeCopy fraction:1.0];

    CGImageRef outImage = CGBitmapContextCreateImage(context);
    CFURLRef outURL = (CFURLRef)[NSURL fileURLWithPath:newFilePath];
    CGImageDestinationRef outDestination = CGImageDestinationCreateWithURL(outURL, kUTTypeJPEG, 1, NULL);
    CGImageDestinationAddImage(outDestination, outImage, NULL);
    if(!CGImageDestinationFinalize(outDestination))
    {
        NSLog(@"Failed to write image to %@", newFilePath);
    }
    CFRelease(outDestination);
    CGImageRelease(outImage);
    CGContextRelease(context);
    CGColorSpaceRelease(rgbColorspace);
}

Answer 7

To resize image

- (NSImage *)scaleImage:(NSImage *)anImage newSize:(NSSize)newSize
{
    NSImage *sourceImage = anImage;
    if ([sourceImage isValid])
    {
        if (anImage.size.width == newSize.width && anImage.size.height == newSize.height && newSize.width <= 0 && newSize.height <= 0) {
            return anImage;
        }

        NSRect oldRect = NSMakeRect(0.0, 0.0, anImage.size.width, anImage.size.height);
        NSRect newRect = NSMakeRect(0,0,newSize.width,newSize.height);
        NSImage *newImage = [[NSImage alloc] initWithSize:newSize];

        [newImage lockFocus];
        [sourceImage drawInRect:newRect fromRect:oldRect operation:NSCompositeCopy fraction:1.0];
        [newImage unlockFocus];

        return newImage;
    }
}