Image getting bigger after saving it

Question

I would be grateful if anyone could help me to solve an issue with image saving. I've got an app which contains recipes with corresponding images. I need to resize them in order to preserve memory and make my app more robust. Everything looks ok the UIImage has proper dimensions. But when I save this image to Documents it appears to become something like twice bigger than it should be.

The code I use for image resizing:

+(UIImage *) createImageFromImage: (UIImage *)image WithName:(NSString *)name Thumbnail: (BOOL)isThumbnail{
CGSize oldSize = image.size;
CGSize newSize;
CGFloat scaleFactor;
if (isThumbnail) {
    name = [NSString stringWithFormat:@"t_%@", name];
    newSize = CGSizeMake(125, 92);
}
else{
    newSize = CGSizeMake(320, 240);
}

if (!CGSizeEqualToSize(newSize, oldSize)) {
    CGFloat widthFactor = newSize.width/oldSize.width;
    CGFloat heightFactor = newSize.height/oldSize.height;

    if (((widthFactor > heightFactor)||(heightFactor > 1))&&(widthFactor < 1)) {
        scaleFactor = widthFactor;
    }
    else{
        scaleFactor = heightFactor;
    }

    newSize.width = scaleFactor*oldSize.width;
    newSize.height = scaleFactor*oldSize.height;
}

NSArray *paths = NSSearchPathForDirectoriesInDomains(NSDocumentDirectory, NSUserDomainMask, YES);
NSString *documentsDirectory = [paths objectAtIndex:0];
NSString *path = [documentsDirectory stringByAppendingPathComponent:name];

UIImage *newImage = nil;
newImage = [self drawImage:image InContextWithSize:newSize];
[UIImagePNGRepresentation(newImage) writeToFile:path atomically:YES];

return newImage;
}




+(UIImage *)drawImage: (UIImage *)image InContextWithSize: (CGSize) newSize {
UIImage *newImage;
UIGraphicsBeginImageContextWithOptions(newSize, NO, 0.0);
[image drawInRect:CGRectMake(0, 0, newSize.width, newSize.height)];
newImage = UIGraphicsGetImageFromCurrentImageContext();
UIGraphicsEndImageContext();

return newImage;
}

Answer 1

The issue appeared to deal with the standard Xcode PNG compression option. One just needs to set it to NO if he doesn't wan't this to happen. I guess that this was made for the sake of retina displays.

Answer 2

I have just changed few lines of code to get scaleFactor

-(UIImage *) createImageFromImage: (UIImage *)image WithName:(NSString *)name Thumbnail: (BOOL)isThumbnail{
    CGSize oldSize = image.size;
    CGSize newSize;
    CGFloat scaleFactorForWidth = 0.0,scaleFactorForHeight= 0.0;
    if (isThumbnail) {
        name = [NSString stringWithFormat:@"t_%@", name];
        newSize = CGSizeMake(125, 92);
    }
    else{
        newSize = CGSizeMake(320, 240);
    }

    if (!CGSizeEqualToSize(newSize, oldSize)) {
        CGFloat widthFactor = newSize.width/oldSize.width;
        CGFloat heightFactor = newSize.height/oldSize.height;

        if (widthFactor != 1) {
            scaleFactorForWidth = widthFactor;
             newSize.width = scaleFactorForWidth*oldSize.width;
        }

        if (heightFactor != 1) {
            scaleFactorForHeight = heightFactor;
               newSize.height = scaleFactorForHeight*oldSize.height;
        }
    }

    NSLog(@"New Size : (%f,%f)",newSize.width,newSize.height);

    NSArray *paths = NSSearchPathForDirectoriesInDomains(NSDocumentDirectory, NSUserDomainMask, YES);
    NSString *documentsDirectory = [paths objectAtIndex:0];
    NSString *path = [documentsDirectory stringByAppendingPathComponent:name];

    UIImage *newImage = nil;
    newImage = [self drawImage:image InContextWithSize:newSize];
    [UIImagePNGRepresentation(newImage) writeToFile:path atomically:YES];

    return newImage;
}