NSImage size not real size with some pictures?

Question

I see that sometimes NSImage size is not real size (with some pictures) and CIImage size is always real. I was testing with this image.

This is source code which I wrote for testing:

NSImage *_imageNSImage = [[NSImage alloc]initWithContentsOfFile:@"<path to image>"];

NSSize _dimensions = [_imageNSImage size];

[_imageNSImage release];

NSLog(@"Width from CIImage: %f",_dimensions.width);
NSLog(@"Height from CIImage: %f",_dimensions.height);




NSURL *_myURL = [NSURL fileURLWithPath:@"<path to image>"];
CIImage *_imageCIImage = [CIImage imageWithContentsOfURL:_myURL];


NSRect _rectFromCIImage = [_imageCIImage extent];

NSLog(@"Width from CIImage: %f",_rectFromCIImage.size.width);
NSLog(@"Height from CIImage: %f",_rectFromCIImage.size.height);

And output is:

enter image description here

So how that can be?? Maybe I'm doing something wrong?

Thanks for the great Wallpaper! – JustSid Feb 13 '12 at 17:53 — JustSid, Feb 13 '12 at 17:53

David Kennedy of Zenopolis · Accepted Answer · 2012-02-14T11:44:32.253

44

NSImage size method returns size information that is screen resolution dependent. To get the size represented in the actual file image you need to use an NSImageRep. You can get an NSImageRep from an NSImage using the representations method. Alternatively you can create a NSBitmapImageRep subclass instance directly like this:

NSArray * imageReps = [NSBitmapImageRep imageRepsWithContentsOfFile:@"<path to image>"];

NSInteger width = 0;
NSInteger height = 0;

for (NSImageRep * imageRep in imageReps) {
    if ([imageRep pixelsWide] > width) width = [imageRep pixelsWide];  
    if ([imageRep pixelsHigh] > height) height = [imageRep pixelsHigh];  
}

NSLog(@"Width from NSBitmapImageRep: %f",(CGFloat)width);
NSLog(@"Height from NSBitmapImageRep: %f",(CGFloat)height);

The loop takes into account that some image formats may contain more than a single image (such as TIFFs for example).

You can create an NSImage at this size by using the following:

NSImage * imageNSImage = [[NSImage alloc] initWithSize:NSMakeSize((CGFloat)width, (CGFloat)height)];
[imageNSImage addRepresentations:imageReps];

edited Feb 14 '12 at 11:44

answered Feb 13 '12 at 17:50

David Kennedy of Zenopolis

904
8
12

Thanks, but one more question. Now I know real size, but NSImage is small in that size.. how to avoid this? I need to use NSImage. For Example I change NSView frame to real size of image but in that frame NSImage is drawned small. – Justin Boo Feb 14 '12 at 08:49
I've made some changes to the answer that should help. – David Kennedy of Zenopolis Feb 14 '12 at 11:45
Nice. I've swift-ified this below for people who prefer that language :) – Ash Jul 22 '16 at 09:41
Great answer. I have been working with lots of image sets and I just encountered this for the first time. Looking through the image metadata I don't seeing anything that indicates the image should be read at a lower resolution. Also, it is a JPEG image, but contains TIFF metadata? Why does NSImage decide to use a smaller representation in some cases? – wcochran Feb 07 '21 at 02:39
I just ran into a case where I read an 2008x1340 JPEG and NSImage reports its size to be a whopping 144576 x 96480. The imageRep pixels size is the correct 2008x1340. So much for choosing the largest. Hmmm... – wcochran Mar 31 '21 at 20:29

Валерий Кобзарь · Answer 2 · 2015-10-17T22:52:17.807

NSImage size method return size in points. To get size represented in pixels you need inspect NSImage.representations property that contains an array of NSImageRep objects with pixelWide/pixelHigh properties and simple change size NSImage object:

@implementation ViewController {
    __weak IBOutlet NSImageView *imageView;
}

- (void)viewDidLoad {
    [super viewDidLoad];
    // Do view setup here.

    NSImage *image = [[NSImage alloc] initWithContentsOfFile:@"/Users/username/test.jpg"];

    if (image.representations && image.representations.count > 0) {
        long lastSquare = 0, curSquare;
        NSImageRep *imageRep;
        for (imageRep in image.representations) {
            curSquare = imageRep.pixelsWide * imageRep.pixelsHigh;
            if (curSquare > lastSquare) {
                image.size = NSMakeSize(imageRep.pixelsWide, imageRep.pixelsHigh);
                lastSquare = curSquare;
            }
        }

        imageView.image = image;
        NSLog(@"%.0fx%.0f", image.size.width, image.size.height);
    }
}

@end

score 5 · Answer 3 · answered Jul 22 '16 at 09:40

Thanks to Zenopolis for the original ObjC code, here's a nice concise Swift version:

func sizeForImageAtURL(url: NSURL) -> CGSize? {
        guard let imageReps = NSBitmapImageRep.imageRepsWithContentsOfURL(url) else { return nil }
        return imageReps.reduce(CGSize.zero, combine: { (size: CGSize, rep: NSImageRep) -> CGSize in
            return CGSize(width: max(size.width, CGFloat(rep.pixelsWide)), height: max(size.height, CGFloat(rep.pixelsHigh)))
        })
    }

score 2 · Answer 4 · answered Oct 08 '17 at 22:43

If your file contains only one image, you can just use this :

let rep = image.representations[0]
let imageSize = NSSize(width: rep.pixelsWide, height: rep.pixelsHigh)

image is your NSImage, imageSize is the image size in pixels.

Copied and updated here: https://stackoverflow.com/a/13228091/3608824

NSImage size not real size with some pictures?

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