How to resize NSImage?

Question

I have an NSBitmapImageRep which is WxH size.

I create NSImage and call addRepresentation:. Then I n

Answer 1

Actually it is not necessary to modify any source image parameters like size. The following snippet is already in Swift, but I think you can infer the Objective-C version from it:

func resized(to: CGSize) -> NSImage {
    let img = NSImage(size: to)

    img.lockFocus()
    defer {
        img.unlockFocus()
    }

    if let ctx = NSGraphicsContext.current {
        ctx.imageInterpolation = .high
        draw(in: NSRect(origin: .zero, size: to),
             from: NSRect(origin: .zero, size: size),
             operation: .copy,
             fraction: 1)
    }

    return img
}

Answer 2

Here is a Swift 3 version keeping ratio of image, just set minimumSize as the minimum height or width you want:

func imageResized(image: NSImage) -> NSImage {
    let ratio = image.size.height / image.size.width

    let width: CGFloat
    let height: CGFloat
    // We keep ratio of image
    if ratio > 1 {
        width = minimumSize
        height = minimumSize * ratio
    } else {
        width = minimumSize
        height = minimumSize * (1 / ratio)
    }
    let destSize = NSSize(width: width, height: height)

    let newImage = NSImage(size: destSize)
    newImage.lockFocus()
    image.draw(in: NSRect(x: 0, y: 0, width: destSize.width, height: destSize.height), from: NSRect(x: 0, y: 0, width: image.size.width, height: image.size.height), operation: .sourceOver, fraction: 1.0)
    newImage.unlockFocus()
    newImage.size = destSize
    return NSImage(data: newImage.tiffRepresentation!)!
}

Answer 3

2020 | SWIFT 4 and 5:

usage:

let resizedImg = someImage.resizedCopy(w: 500.0, h:500.0)
let scaledImg = someImage.scaledCopy( sizeOfLargerSide: 1000.0)

//and bonus:
scaledImg.writePNG(toURL: someUrl )

code:

extension NSImage {
    func scaledCopy( sizeOfLargerSide: CGFloat) ->  NSImage {
        var newW: CGFloat
        var newH: CGFloat
        var scaleFactor: CGFloat
        
        if ( self.size.width > self.size.height) {
            scaleFactor = self.size.width / sizeOfLargerSide
            newW = sizeOfLargerSide
            newH = self.size.height / scaleFactor
        }
        else{
            scaleFactor = self.size.height / sizeOfLargerSide
            newH = sizeOfLargerSide
            newW = self.size.width / scaleFactor
        }
        
        return resizedCopy(w: newW, h: newH)
    }
    
    
    func resizedCopy( w: CGFloat, h: CGFloat) -> NSImage {
        let destSize = NSMakeSize(w, h)
        let newImage = NSImage(size: destSize)
        
        newImage.lockFocus()
        
        self.draw(in: NSRect(origin: .zero, size: destSize),
                  from: NSRect(origin: .zero, size: self.size),
                  operation: .copy,
                  fraction: CGFloat(1)
        )
        
        newImage.unlockFocus()
        
        guard let data = newImage.tiffRepresentation,
              let result = NSImage(data: data)
        else { return NSImage() }
        
        return result
    }
    
    public func writePNG(toURL url: URL) {
        guard let data = tiffRepresentation,
              let rep = NSBitmapImageRep(data: data),
              let imgData = rep.representation(using: .png, properties: [.compressionFactor : NSNumber(floatLiteral: 1.0)]) else {

            Swift.print("\(self) Error Function '\(#function)' Line: \(#line) No tiff rep found for image writing to \(url)")
            return
        }

        do {
            try imgData.write(to: url)
        }catch let error {
            Swift.print("\(self) Error Function '\(#function)' Line: \(#line) \(error.localizedDescription)")
        }
    }
}

Answer 4

EDIT You can resize image using below function:

- (NSImage *)imageResize:(NSImage*)anImage
         newSize:(NSSize)newSize 
{
 NSImage *sourceImage = anImage;
 [sourceImage setScalesWhenResized:YES];

 // Report an error if the source isn't a valid image
 if (![sourceImage isValid])
 {
    NSLog(@"Invalid Image");
 } else
 {
    NSImage *smallImage = [[[NSImage alloc] initWithSize: newSize] autorelease];
    [smallImage lockFocus];
    [sourceImage setSize: newSize];
    [[NSGraphicsContext currentContext] setImageInterpolation:NSImageInterpolationHigh];
    [sourceImage compositeToPoint:NSZeroPoint operation:NSCompositeCopy];
    [smallImage unlockFocus];
    return smallImage;
 }
 return nil;
}

Secondly like this:

NSData *imageData = [yourImg  TIFFRepresentation]; // converting img into data
NSBitmapImageRep *imageRep = [NSBitmapImageRep imageRepWithData:imageData]; // converting into BitmapImageRep 
NSDictionary *imageProps = [NSDictionary dictionaryWithObject:[NSNumber numberWithFloat:0.9] forKey:NSImageCompressionFactor]; // any number betwwen 0 to 1
imageData = [imageRep representationUsingType:NSJPEGFileType properties:imageProps]; // use NSPNGFileType if needed
NSImage *resizedImage = [[NSImage alloc] initWithData:imageData]; // image created from data