How to rapidly create an NSMutableArray with CFDataRef image pixel data in Xcode for iOS - objective-c

Question

My question is simple, I have the following code, it creates an array of Hues got from a function that returns the UIColor of an image (this is not important, just context). So, I need to create this array as fast as possible, this test runs with only a 5x5 pixels image and it takes about 3sec, I want to be able to run a 50x50 pixels image (at least) in about 2 secods (tops), any ideas?
- (void)createArrayOfHues: (UIImage *)imageScaned{
if (imageScaned != nil) {
NSLog(#"Creating Array...");
UIImageView *img = [[UIImageView alloc] initWithFrame:CGRectMake(0, 0, 5, 5)];
img.contentMode = UIViewContentModeScaleToFill;
img.image = imageScaned;
img.contentMode = UIViewContentModeRedraw;
img.hidden = YES;
int i = 0;
CGFloat hue = 0;
CGFloat sat = 0;
CGFloat brit = 0;
CGFloat alph = 0;
CGFloat hue2 = 0;
CGFloat sat2 = 0;
CGFloat brit2 = 0;
CGFloat alph2 = 0;
[_colorsArray removeAllObjects];
[_satForHue removeAllObjects];
[_britForHue removeAllObjects];
[_alphForHue removeAllObjects];
_colorsArray = [[NSMutableArray alloc] initWithCapacity:(25)];
_satForHue = [[NSMutableArray alloc] initWithCapacity:(25)];
_britForHue = [[NSMutableArray alloc] initWithCapacity:(25)];
_alphForHue = [[NSMutableArray alloc] initWithCapacity:(25)];
while (i<25) {
for (int y=1; y <= 5; y++){
for (int x = 1; x <= 2.5; x++){
if (x != (5-x)){
UIColor *color = [self colorMatch:imageScaned :x :y];
UIColor *color2 = [self colorMatch:imageScaned :(5-x) :y];
if([color getHue:&hue saturation:&sat brightness:&brit alpha:&alph] && [color2 getHue:&hue2 saturation:&sat2 brightness:&brit2 alpha:&alph2]){
NSNumber *hueId = [NSNumber numberWithFloat:(float)hue];
NSNumber *satId = [NSNumber numberWithFloat:(float)sat];
NSNumber *britId = [NSNumber numberWithFloat:(float)brit];
NSNumber *alphId = [NSNumber numberWithFloat:(float)alph];
NSNumber *hueId2 = [NSNumber numberWithFloat:(float)hue2];
NSNumber *satId2 = [NSNumber numberWithFloat:(float)sat2];
NSNumber *britId2 = [NSNumber numberWithFloat:(float)brit2];
NSNumber *alphId2 = [NSNumber numberWithFloat:(float)alph2];
[_colorsArray insertObject:hueId atIndex:i];
[_satForHue insertObject:satId atIndex:i];
[_britForHue insertObject:britId atIndex:i];
[_alphForHue insertObject:alphId atIndex:i];
[_colorsArray insertObject:hueId2 atIndex:(i+1)];
[_satForHue insertObject:satId2 atIndex:(i+1)];
[_britForHue insertObject:britId2 atIndex:(i+1)];
[_alphForHue insertObject:alphId2 atIndex:(i+1)];
}
NSLog(#"color inserted at %i with x: %i and y: %i" , i , x, y);
i++;
}else {
UIColor *color = [self colorMatch:imageScaned :x :y];
if([color getHue:&hue saturation:&sat brightness:&brit alpha:&alph]){
NSNumber *hueId = [NSNumber numberWithFloat:(float)hue];
NSNumber *satId = [NSNumber numberWithFloat:(float)sat];
NSNumber *britId = [NSNumber numberWithFloat:(float)brit];
NSNumber *alphId = [NSNumber numberWithFloat:(float)alph];
[_colorsArray insertObject:hueId atIndex:i];
[_satForHue insertObject:satId atIndex:i];
[_britForHue insertObject:britId atIndex:i];
[_alphForHue insertObject:alphId atIndex:i];
}
}
}
}
}
NSLog(#"Returns the array");
}else{
NSLog(#"Returns nothing");
}
}
The code for colorMatch:
- (UIColor *) colorMatch: (UIImage *)image :(int) x :(int) y {
isBlackColored = NO;
if (image == nil){
NSUserDefaults *defaults = [NSUserDefaults standardUserDefaults];
BOOL customColor = [defaults boolForKey:#"custom_color"];
if (customColor){
float red = [defaults floatForKey:#"custom_color_slider_red"];
float green = [defaults floatForKey:#"custom_color_slider_green"];
float blue = [defaults floatForKey:#"custom_color_slider_blue"];
return [UIColor colorWithRed:red green:green blue:blue alpha:1];
}else
isDefaultS = YES;
}
else{
CFDataRef pixelData = CGDataProviderCopyData(CGImageGetDataProvider(image.CGImage));
const UInt8* data = CFDataGetBytePtr(pixelData);
int pixelInfo = ((image.size.width * y) + x ) * 4;
UInt8 red = data[pixelInfo];
UInt8 green = data[(pixelInfo + 1)];
UInt8 blue = data[pixelInfo + 2];
UInt8 alpha = data[pixelInfo + 3];
CFRelease(pixelData);
float redC = red/255.0f;
float greenC = green/255.0f;
float blueC = blue/255.0f;
UIColor* color = [UIColor colorWithRed:redC green:greenC blue:blueC alpha:alpha/255.0f];
return color;
}
return nil;
}

Answer 1

I think your main performance bottleneck is not the initialization of NSMutableArray instances, but the way you index your image:
UIColor *color = [self colorMatch:imageScaned :x :y];
I guess this method converts the UIImage to a CGImageRef, copies its data, indexes it, then destroys/releases these temporary objects, or something like this - for every single pixel...
You should refactor this code to get hold of the image buffer only once, and then work with it like a regular C pointer/array. If that doesn't solve your performance problem, you should do some profiling.