How to resize the image programmatically in objective-c in iphone

Question

I have an application where I am displaying large images in a small space. The images are quite large, but I am only displaying them in 100x100 pixel frames. My app is responding slowly because of the size fo the images I am using.

To improve performance, how can I resize the images programmatically using Objective-C?

Solution 1

Please find the following code.

- (UIImage *)imageWithImage:(UIImage *)image convertToSize:(CGSize)size {
    UIGraphicsBeginImageContext(size);
    [image drawInRect:CGRectMake(0, 0, size.width, size.height)];
    UIImage *destImage = UIGraphicsGetImageFromCurrentImageContext();    
    UIGraphicsEndImageContext();
    return destImage;
}

Solution 2

This code is for just change image scale not for resizing. You have to set CGSize as your image width and hight so the image will not stretch and it arrange at the middle.

- (UIImage *)imageWithImage:(UIImage *)image scaledToFillSize:(CGSize)size
{
    CGFloat scale = MAX(size.width/image.size.width, size.height/image.size.height);
    CGFloat width = image.size.width * scale;
    CGFloat height = image.size.height * scale;
    CGRect imageRect = CGRectMake((size.width - width)/2.0f,
                                  (size.height - height)/2.0f,
                                  width,
                                  height);

    UIGraphicsBeginImageContextWithOptions(size, NO, 0);
    [image drawInRect:imageRect];
    UIImage *newImage = UIGraphicsGetImageFromCurrentImageContext();
    UIGraphicsEndImageContext();
    return newImage;
}

Solution 3

My favorite way to do this is with CGImageSourceCreateThumbnailAtIndex (in the ImageIO framework). The name is a bit misleading.

Here's an excerpt of some code from a recent app of mine.

CGFloat maxw = // whatever;
CGFloat maxh = // whatever;

CGImageSourceRef src = NULL;
if ([imageSource isKindOfClass:[NSURL class]])
    src = CGImageSourceCreateWithURL((__bridge CFURLRef)imageSource, nil);
else if ([imageSource isKindOfClass:[NSData class]])
    src = CGImageSourceCreateWithData((__bridge CFDataRef)imageSource, nil);

// if at double resolution, double the thumbnail size and use double-resolution image
CGFloat scale = 1;
if ([[UIScreen mainScreen] scale] > 1.0) {
    scale = 2;
    maxw *= 2;
    maxh *= 2;
}

// load the image at the desired size
NSDictionary* d = @{
                    (id)kCGImageSourceShouldAllowFloat: (id)kCFBooleanTrue,
                    (id)kCGImageSourceCreateThumbnailWithTransform: (id)kCFBooleanTrue,
                    (id)kCGImageSourceCreateThumbnailFromImageAlways: (id)kCFBooleanTrue,
                    (id)kCGImageSourceThumbnailMaxPixelSize: @((int)(maxw > maxh ? maxw : maxh))
                    };
CGImageRef imref = CGImageSourceCreateThumbnailAtIndex(src, 0, (__bridge CFDictionaryRef)d);
if (NULL != src)
    CFRelease(src);
UIImage* im = [UIImage imageWithCGImage:imref scale:scale orientation:UIImageOrientationUp];
if (NULL != imref)
    CFRelease(imref);

Solution 4

If you are using a image on different sizes and resizing each time it will degrade your app performance. Solution is don't resize them just use button in place of imageview. and just set the image on button it will resize automatically and you will get great performance.

I was also resizing images while setting it on cell but my app got slow So I used Button in place of imageview (not resizing images programatically button is doing this job) and it is working perfectly fine.

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