PNG representation of NSImage

gistfile1.m

//
//  GRAppDelegate.m
//  Testme
//
//  Created by Marco Tabini on 11-08-29.
//  Copyright (c) 2011 Marco Tabini. All rights reserved.
//

#import "GRAppDelegate.h"

@implementation GRAppDelegate

@synthesize window = _window;

// Note this uses ARC. Modify as needed for traditional retain/release management

// Grab a screenshot from the main screen

- (NSImage *)captureImageForRect:(NSRect)rect {
    CGImageRef screenShot = CGWindowListCreateImage(CGRectInfinite, kCGWindowListOptionOnScreenOnly, kCGNullWindowID, kCGWindowImageDefault);
    NSBitmapImageRep *imageRep = [[NSBitmapImageRep alloc] initWithCGImage:screenShot];
    
    NSImage *result = [[NSImage alloc] init];
    
    [result addRepresentation:imageRep];
    
    return result;
}


- (NSData *) PNGRepresentationOfImage:(NSImage *) image {
    // Create a bitmap representation from the current image
    
    [image lockFocus];
    NSBitmapImageRep *bitmapRep = [[NSBitmapImageRep alloc] initWithFocusedViewRect:NSMakeRect(0, 0, image.size.width, image.size.height)];
    [image unlockFocus];
    
    return [bitmapRep representationUsingType:NSPNGFileType properties:Nil];
}


- (void)applicationDidFinishLaunching:(NSNotification *)aNotification {
    // Take a screenshot
    
    NSImage *screenshot = [self captureImageForRect:[[NSScreen mainScreen] frame]];
    
    // Resize it to 50%. This will cause finalImage to contain a NSCGImageSnapshotRep
    
    NSSize newSize = NSMakeSize(screenshot.size.width / 2, screenshot.size.height / 2);
    
    NSImage *finalImage = [[NSImage alloc] initWithSize:newSize];
    
    [finalImage lockFocus];
    [screenshot drawInRect:NSMakeRect(0, 0, newSize.width, newSize.height) 
                  fromRect:NSMakeRect(0, 0, screenshot.size.width, screenshot.size.height)
                 operation:NSCompositeSourceOver
                  fraction:1.0];
    [finalImage unlockFocus];
    
    // Now create a PNG representation of the image. This should work regardless
    // of the format of its existing representations
    
    NSData *pngRep = [self PNGRepresentationOfImage:finalImage];
    
    // Write it to the desktop
    
    [pngRep writeToFile:[@"~/Desktop/screenshot.png" stringByExpandingTildeInPath]
             atomically:NO];
    
    // Close app
    
    [NSApp terminate:self];
}

@end