Bitmap Average using Accelerate.framework

main.m

//
//  main.m
//  BitmapAverage
//
//  Created by Alex Nichol on 4/8/14.
//  Copyright (c) 2014 Alex Nichol. All rights reserved.
//

#import <Foundation/Foundation.h>
#import <Accelerate/Accelerate.h>
#import "ANImageBitmapRep.h"

int main(int argc, const char * argv[]) {
  @autoreleasepool {
    NSLog(@"start");
    
    // load our images
    NSImage * img1 = [[NSImage alloc] initWithContentsOfFile:@"/Users/alex/Desktop/foobar.png"];
    NSImage * img2 = [[NSImage alloc] initWithContentsOfFile:@"/Users/alex/Desktop/foobar.jpg"];
    ANImageBitmapRep * irep1 = [[ANImageBitmapRep alloc] initWithImage:img1];
    ANImageBitmapRep * irep2 = [[ANImageBitmapRep alloc] initWithImage:img2];
    
    // the output bitmap rep is created using a size because we will be outputting raw pixels to it
    ANImageBitmapRep * dest = [[ANImageBitmapRep alloc] initWithSize:irep1.bitmapSize];
    
    long pixelCount = irep1.bitmapSize.x * irep1.bitmapSize.y;
    
    // our input buffer needs to have the ARGB (in float from) of BOTH images (thus 8 components per pixel)
    float * buffer = malloc(sizeof(float) * (pixelCount * 8));
    
    // our output buffer is an image, so only 4 components per pixel needed
    float * result = malloc(sizeof(float) * (pixelCount * 4));

    // cast the first bitmap into floats
    vDSP_vfltu8(irep1.bitmapData, 1, buffer, 1, pixelCount * 4);
    
    // same for the second
    vDSP_vfltu8(irep2.bitmapData, 1, &buffer[pixelCount * 4], 1, pixelCount * 4);
    
    // matrix to average the two vectors
    float leftMatrix[] = {
      0.5f, 0.5f
    };
    
    vDSP_mmul(leftMatrix, 1, buffer, 1, result, 1, 1, pixelCount * 4, 2);
    free(buffer);
    
    // use another vectorized cast to get our output back into bytes
    vDSP_vfixu8(result, 1, dest.bitmapData, 1, pixelCount * 4);
    free(result);
    
    NSLog(@"done averaging");
    
    // tell the output we modified its buffer
    [dest setNeedsUpdate:YES];
    [[dest.image TIFFRepresentation] writeToFile:@"/Users/alex/Desktop/merged.tiff" atomically:YES];
    
    NSLog(@"done write to TIFF");
  }
  return 0;
}