I abandoned that vocaro.com solution for other reasons (that solution would crash when used with atypical image formats, e.g. CMYK).
Anyway, I now use the imageByScalingAspectFillSize method of the following UIImage category to make my square thumbnails.
By the way, this automatically applies the scale of the main screen of the device (e.g. UIButton button that is is 60×60 points on a Retina device, this will apply that scale of 2x (or 3x), i.e. a 120×120 or 180×180 image).
UIImage+SimpleResize.h:
/* UIImage+SimpleResize.h
*
* Modified by Robert Ryan on 5/19/11.
*/
@import UIKit;
/** Image resizing category.
*
* Modified by Robert Ryan on 5/19/11.
*
* Inspired by http://ofcodeandmen.poltras.com/2008/10/30/undocumented-uiimage-resizing/
* but adjusted to support AspectFill and AspectFit modes.
*/
@interface UIImage (SimpleResize)
/** Resize the image to be the required size, stretching it as needed.
*
* @param size The new size of the image.
* @param contentMode The `UIViewContentMode` to be applied when resizing image.
* Either `UIViewContentModeScaleToFill`, `UIViewContentModeScaleAspectFill`, or
* `UIViewContentModeScaleAspectFit`.
*
* @return Return `UIImage` of resized image.
*/
- (UIImage * _Nullable)imageByScalingToSize:(CGSize)size contentMode:(UIViewContentMode)contentMode;
/** Resize the image to be the required size, stretching it as needed.
*
* @param size The new size of the image.
* @param contentMode The `UIViewContentMode` to be applied when resizing image.
* Either `UIViewContentModeScaleToFill`, `UIViewContentModeScaleAspectFill`, or
* `UIViewContentModeScaleAspectFit`.
* @param scale The scale factor to apply to the bitmap. If you specify a value of 0.0, the scale factor is set to the scale factor of the device’s main screen.
*
* @return Return `UIImage` of resized image.
*/
- (UIImage * _Nullable)imageByScalingToSize:(CGSize)size contentMode:(UIViewContentMode)contentMode scale:(CGFloat)scale;
/** Crop the image to be the required size.
*
* @param bounds The bounds to which the new image should be cropped.
*
* @return Cropped `UIImage`.
*/
- (UIImage * _Nullable)imageByCroppingToBounds:(CGRect)bounds;
/** Crop the image to be the required size.
*
* @param bounds The bounds to which the new image should be cropped.
* @param scale The scale factor to apply to the bitmap. If you specify a value of 0.0, the scale factor is set to the scale factor of the device’s main screen.
*
* @return Cropped `UIImage`.
*/
- (UIImage * _Nullable)imageByCroppingToBounds:(CGRect)bounds scale:(CGFloat)scale;
/** Resize the image to fill the rectange of the specified size, preserving the aspect ratio, trimming if needed.
*
* @param size The new size of the image.
*
* @return Return `UIImage` of resized image.
*/
- (UIImage * _Nullable)imageByScalingAspectFillSize:(CGSize)size;
/** Resize the image to fill the rectange of the specified size, preserving the aspect ratio, trimming if needed.
*
* @param size The new size of the image.
* @param scale The scale factor to apply to the bitmap. If you specify a value of 0.0, the scale factor is set to the scale factor of the device’s main screen.
*
* @return Return `UIImage` of resized image.
*/
- (UIImage * _Nullable)imageByScalingAspectFillSize:(CGSize)size scale:(CGFloat)scale;
/** Resize the image to be the required size, stretching it as needed.
*
* @param size The new size of the image.
*
* @return Resized `UIImage` of resized image.
*/
- (UIImage * _Nullable)imageByScalingToFillSize:(CGSize)size;
/** Resize the image to be the required size, stretching it as needed.
*
* @param size The new size of the image.
* @param scale The scale factor to apply to the bitmap. If you specify a value of 0.0, the scale factor is set to the scale factor of the device’s main screen.
*
* @return Resized `UIImage` of resized image.
*/
- (UIImage * _Nullable)imageByScalingToFillSize:(CGSize)size scale:(CGFloat)scale;
/** Resize the image to fit within the required size, preserving the aspect ratio, with no trimming taking place.
*
* @param size The new size of the image.
*
* @return Return `UIImage` of resized image.
*/
- (UIImage * _Nullable)imageByScalingAspectFitSize:(CGSize)size;
/** Resize the image to fit within the required size, preserving the aspect ratio, with no trimming taking place.
*
* @param size The new size of the image.
* @param scale The scale factor to apply to the bitmap. If you specify a value of 0.0, the scale factor is set to the scale factor of the device’s main screen.
*
* @return Return `UIImage` of resized image.
*/
- (UIImage * _Nullable)imageByScalingAspectFitSize:(CGSize)size scale:(CGFloat)scale;
@end
UIImage+SimpleResize.m:
// UIImage+SimpleResize.m
//
// Created by Robert Ryan on 5/19/11.
#import "UIImage+SimpleResize.h"
@implementation UIImage (SimpleResize)
- (UIImage *)imageByScalingToSize:(CGSize)size contentMode:(UIViewContentMode)contentMode {
return [self imageByScalingToSize:size contentMode:contentMode scale:0];
}
- (UIImage *)imageByScalingToSize:(CGSize)size contentMode:(UIViewContentMode)contentMode scale:(CGFloat)scale {
if (contentMode == UIViewContentModeScaleToFill) {
return [self imageByScalingToFillSize:size];
}
else if ((contentMode == UIViewContentModeScaleAspectFill) ||
(contentMode == UIViewContentModeScaleAspectFit)) {
CGFloat horizontalRatio = self.size.width / size.width;
CGFloat verticalRatio = self.size.height / size.height;
CGFloat ratio;
if (contentMode == UIViewContentModeScaleAspectFill)
ratio = MIN(horizontalRatio, verticalRatio);
else
ratio = MAX(horizontalRatio, verticalRatio);
CGSize sizeForAspectScale = CGSizeMake(self.size.width / ratio, self.size.height / ratio);
UIImage *image = [self imageByScalingToFillSize:sizeForAspectScale scale:scale];
// if we're doing aspect fill, then the image still needs to be cropped
if (contentMode == UIViewContentModeScaleAspectFill) {
CGRect subRect = CGRectMake(floor((sizeForAspectScale.width - size.width) / 2.0),
floor((sizeForAspectScale.height - size.height) / 2.0),
size.width,
size.height);
image = [image imageByCroppingToBounds:subRect];
}
return image;
}
return nil;
}
- (UIImage *)imageByCroppingToBounds:(CGRect)bounds {
return [self imageByCroppingToBounds:bounds scale:0];
}
- (UIImage *)imageByCroppingToBounds:(CGRect)bounds scale:(CGFloat)scale {
if (scale == 0) {
scale = [[UIScreen mainScreen] scale];
}
CGRect rect = CGRectMake(bounds.origin.x * scale, bounds.origin.y * scale, bounds.size.width * scale, bounds.size.height * scale);
CGImageRef imageRef = CGImageCreateWithImageInRect([self CGImage], rect);
UIImage *croppedImage = [UIImage imageWithCGImage:imageRef scale:scale orientation:self.imageOrientation];
CGImageRelease(imageRef);
return croppedImage;
}
- (UIImage *)imageByScalingToFillSize:(CGSize)size {
return [self imageByScalingToFillSize:size scale:0];
}
- (UIImage *)imageByScalingToFillSize:(CGSize)size scale:(CGFloat)scale {
UIGraphicsBeginImageContextWithOptions(size, false, scale);
[self drawInRect:CGRectMake(0, 0, size.width, size.height)];
UIImage *image = UIGraphicsGetImageFromCurrentImageContext();
UIGraphicsEndImageContext();
return image;
}
- (UIImage *)imageByScalingAspectFillSize:(CGSize)size {
return [self imageByScalingAspectFillSize:size scale:0];
}
- (UIImage *)imageByScalingAspectFillSize:(CGSize)size scale:(CGFloat)scale {
return [self imageByScalingToSize:size contentMode:UIViewContentModeScaleAspectFill scale:scale];
}
- (UIImage *)imageByScalingAspectFitSize:(CGSize)size {
return [self imageByScalingAspectFitSize:size scale:0];
}
- (UIImage *)imageByScalingAspectFitSize:(CGSize)size scale:(CGFloat)scale {
return [self imageByScalingToSize:size contentMode:UIViewContentModeScaleAspectFit scale:scale];
}
@end