Objective-Cで画像のリサイズ系

ImageUtil.m

#import "ImageUtil.h"

@implementation ImageUtil

// 幅を元に、リサイズ画像の幅・高さを算出する
+ (CGSize)resizeFromWidth:(CGFloat)width imageSize:(CGSize)imageSize {
    CGFloat s_x = imageSize.width / width;
    CGFloat s_y = imageSize.height / (imageSize.height / s_x);

    CGFloat scale = MAX(s_x, s_y);
    if (scale > 1) {
        CGFloat new_x = imageSize.width / scale;
        CGFloat new_y = imageSize.height / scale;

        return CGSizeMake(new_x, new_y);
    }

    return imageSize;
}

// 幅を元に、UIImageのリサイズした場合のサイズを返す
+ (CGSize)resizeFromWidth:(CGFloat)width image:(UIImage *)image {
    return [self resizeFromWidth:width imageSize:CGSizeMake(image.size.width, image.size.height)];
}

// 幅を元に、UIImageをリサイズし、UIImageを返す
+ (UIImage *)resizeImageFromWidth:(CGFloat)width image:(UIImage *)image {
    CGSize resizedSize = [self resizeFromWidth:width image:image];

    UIGraphicsBeginImageContext(resizedSize);

    [image drawInRect:CGRectMake(0, 0, resizedSize.width, resizedSize.height)];
    UIImage *resizedImage = UIGraphicsGetImageFromCurrentImageContext();

    UIGraphicsEndImageContext();

    return resizedImage;
}

// 幅・高さを元に、リサイズ画像の幅・高さを算出する
+ (CGSize)resizeFromSize:(CGSize)size imageSize:(CGSize)imageSize {
    CGFloat widthRatio = imageSize.width / size.width;
    CGFloat heightRatio = imageSize.height / size.height;
    CGFloat ratio = (widthRatio < heightRatio) ? widthRatio : heightRatio;
    CGSize resizedSize = CGSizeMake(size.width * ratio, size.height * ratio);

    return resizedSize;
}

// 幅・高さを元に、UIImageをリサイズして、CGSizeを返す
+ (CGSize)resizeFromSize:(CGSize)size image:(UIImage *)image {
    CGFloat widthRatio = size.width / image.size.width;
    CGFloat heightRatio = size.height / image.size.height;
    CGFloat ratio = (widthRatio < heightRatio) ? widthRatio : heightRatio;
    CGSize resizedSize = CGSizeMake(image.size.width * ratio, image.size.height * ratio);

    return resizedSize;
}

// 幅・高さを元に、UIImageをリサイズして、UIImageを返す
+ (UIImage *)resizeImageFromSize:(CGSize)size image:(UIImage *)image {
    CGSize resizedSize = [self resizeFromSize:(CGSize) size image:image];

    UIGraphicsBeginImageContext(resizedSize);

    [image drawInRect:CGRectMake(0, 0, resizedSize.width, resizedSize.height)];
    UIImage *resizedImage = UIGraphicsGetImageFromCurrentImageContext();

    UIGraphicsEndImageContext();

    return resizedImage;
}