CODEWITHSUNDEEP
uiimage
MDM
MDM

Reputation: 11

How can I compress a UIImage?

I'm writing an iPhone app to create a screen capture and email it as a png or jpg. How can I compress the image to reduce file size?

Here is my code for capturing the image:

UIGraphicsBeginImageContext(containerView.frame.size);
[self.view.layer renderInContext:UIGraphicsGetCurrentContext()];
UIImage *viewImage = UIGraphicsGetImageFromCurrentImageContext();
UIGraphicsEndImageContext();

// launch mail app
[self performSelector:@selector(sendImage:) withObject:viewImage afterDelay:0.5];

Upvotes: 1

Views: 695

Answers (2)

qipei
qipei

Reputation: 1

#import "UIImage+Compress.h"

#define MAX_IMAGEPIX 200.0          // max pix 200.0px
#define MAX_IMAGEDATA_LEN 50000.0   // max data length 5K

@implementation UIImage (Compress)

- (UIImage *)compressedImage {
    CGSize imageSize = self.size;
    CGFloat width = imageSize.width;
    CGFloat height = imageSize.height;

    if (width <= MAX_IMAGEPIX && height <= MAX_IMAGEPIX) {
        // no need to compress.
        return self;
    }

    if (width == 0 || height == 0) {
        // void zero exception
         return self;
    }

    UIImage *newImage = nil;
    CGFloat widthFactor = MAX_IMAGEPIX / width;
    CGFloat heightFactor = MAX_IMAGEPIX / height;
    CGFloat scaleFactor = 0.0;

    if (widthFactor > heightFactor)
        scaleFactor = heightFactor; // scale to fit height
    else
        scaleFactor = widthFactor; // scale to fit width

    CGFloat scaledWidth  = width * scaleFactor;
    CGFloat scaledHeight = height * scaleFactor;
    CGSize targetSize = CGSizeMake(scaledWidth, scaledHeight);

    UIGraphicsBeginImageContext(targetSize); // this will crop

    CGRect thumbnailRect = CGRectZero;
    thumbnailRect.size.width  = scaledWidth;
    thumbnailRect.size.height = scaledHeight;

    [self drawInRect:thumbnailRect];

    newImage = UIGraphicsGetImageFromCurrentImageContext();

    //pop the context to get back to the default
    UIGraphicsEndImageContext();

    return newImage;

}

- (NSData *)compressedData:(CGFloat)compressionQuality {
    assert(compressionQuality <= 1.0 && compressionQuality >= 0);

    return UIImageJPEGRepresentation(self, compressionQuality);
}

- (CGFloat)compressionQuality {
    NSData *data = UIImageJPEGRepresentation(self, 1.0);
    NSUInteger dataLength = [data length];

    if(dataLength > MAX_IMAGEDATA_LEN) {
        return 1.0 - MAX_IMAGEDATA_LEN / dataLength;
    } else {
        return 1.0;
    }
}

- (NSData *)compressedData {
    CGFloat quality = [self compressionQuality];

    return [self compressedData:quality];
}

@end

Upvotes: 0

Bruce Dean
Bruce Dean

Reputation: 2828

A similar question is answered here on the Stack. The only difference is that you are using UIImage, but this shouldn't hold you back, I think the general approach can still work. You can even set the compression factor programatically.

Hope this helps!

Upvotes: 1

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