Set pHYs chunk (DPI) of PNG

main.m

@import AppKit;
@import ImageIO;
@import CoreServices;

#define fromCF (__bridge id)
#define toCF (__bridge CFTypeRef)

int main(int argc, const char * argv[]) {
    @autoreleasepool {
        CGRect rect = CGRectMake(0, 0, 100, 100);
        NSImage *nsImage = [NSImage imageWithSize:rect.size flipped:NO drawingHandler:^BOOL(NSRect dstRect) {
            [NSColor.whiteColor set];
            NSRectFill(CGRectInfinite);
            [NSColor.redColor set];
            [[NSBezierPath bezierPathWithOvalInRect:CGRectInset(rect, 10, 10)] fill];
            return YES;
        }];

        CGImageRef cgImage = [nsImage CGImageForProposedRect:&rect context:nil hints:nil];

        NSURL *url = [NSURL fileURLWithPath:@"/tmp/test.png"];
        CGImageDestinationRef dest = CGImageDestinationCreateWithURL(toCF url, kUTTypePNG, 1, nil);
        NSDictionary<NSString *, id> *imageProperties = @{ fromCF kCGImagePropertyDPIHeight: @(17), fromCF kCGImagePropertyDPIWidth: @(19) };
        CGImageDestinationAddImage(dest, cgImage, toCF imageProperties);
        CGImageDestinationFinalize(dest);
    }
    return 0;
}