[IOS]当图片太大时，重新调整图片大小

图片分辨率太高，有时候直接放在button里面会导致变形，需要重新缩放图片。

直接上代码：

.h:

@import UIKit;

@interface UIImage (PGResizeImage)

- (UIImage *)convertToGreyscale;
- (UIImage *)resizeImageToDimension:(CGSize)expectedSize;
- (UIImage *)resizeImageWithScaledToSize:(CGSize)newSize;
- (UIImage *)setResizeImageWithSize:(NSInteger)size;
- (UIImage *)waterMarkWithImage:(UIImage *)waterMark;

@end

 .m:

#import "UIImage+PGResizeImage.h"
//#import "PGLogger.h"

@implementation UIImage (PGResizeImage)

- (UIImage *)convertToGreyscale {
    int kRed = 1;
    int kGreen = 2;
    int kBlue = 4;
    
    int colors = kGreen | kBlue | kRed;
    int m_width = self.size.width;
    int m_height = self.size.height;
    
    uint32_t *rgbImage = (uint32_t *) malloc(m_width * m_height * sizeof(uint32_t));
    CGColorSpaceRef colorSpace = CGColorSpaceCreateDeviceRGB();
    CGContextRef context = CGBitmapContextCreate(rgbImage, m_width, m_height, 8, m_width * 4, colorSpace, kCGBitmapByteOrder32Little | kCGImageAlphaNoneSkipLast);
    CGContextSetInterpolationQuality(context, kCGInterpolationHigh);
    CGContextSetShouldAntialias(context, NO);
    CGContextDrawImage(context, CGRectMake(0, 0, m_width, m_height), [self CGImage]);
    CGContextRelease(context);
    CGColorSpaceRelease(colorSpace);
    
    uint8_t *m_imageData = (uint8_t *) malloc(m_width * m_height);
    for(int y = 0; y < m_height; y++) {
        for(int x = 0; x < m_width; x++) {
            uint32_t rgbPixel = rgbImage[y * m_width + x];
            uint32_t sum = 0,count = 0;
            if (colors & kRed) {
                sum += (rgbPixel >> 24)&255; count++;
            }
            if (colors & kGreen) {
                sum += (rgbPixel >> 16)&255; count++;
            }
            if (colors & kBlue) {
                sum += (rgbPixel >> 8)&255; count++;
            }
            m_imageData[y*m_width+x]=sum/count;
        }
    }
    free(rgbImage);
    
    uint8_t *result = (uint8_t *) calloc(m_width * m_height *sizeof(uint32_t), 1);
    for(int i = 0; i < m_height * m_width; i++) {
        result[i * 4] = 0;
        int val = m_imageData[i];
        result[i * 4 + 1]=val;
        result[i * 4 + 2]=val;
        result[i * 4 + 3]=val;
    }
    
    colorSpace = CGColorSpaceCreateDeviceRGB();
    context = CGBitmapContextCreate(result, m_width, m_height, 8, m_width * sizeof(uint32_t), colorSpace, kCGBitmapByteOrder32Little | kCGImageAlphaNoneSkipLast);
    CGImageRef imageRef = CGBitmapContextCreateImage(context);
    CGContextRelease(context);
    CGColorSpaceRelease(colorSpace);
    UIImage *resultUIImage = [UIImage imageWithCGImage:imageRef];
    CGImageRelease(imageRef);
    free(m_imageData);
    [NSData dataWithBytesNoCopy:result length:m_width * m_height];
    
    return resultUIImage;
}

- (UIImage *)resizeImageToDimension:(CGSize)expectedSize {
//    DDLogInfo(@"%@ originalSize: %@, expectedSize: %@", NSStringFromSelector(_cmd), NSStringFromCGSize(self.size), NSStringFromCGSize(expectedSize));
    
    CGFloat totalExpectedSize = expectedSize.height * expectedSize.width;
    
    if (totalExpectedSize < self.size.height * self.size.width) {
        
        CGFloat ratio;
        if (self.size.width < self.size.height) {
            expectedSize = CGSizeMake(expectedSize.height, expectedSize.width);
            ratio = self.size.width / expectedSize.width;
        }
        else if (self.size.height < self.size.width) {
            ratio = self.size.height / expectedSize.height;
        }
        else {
            ratio = self.size.height / MIN(expectedSize.height, expectedSize.width);
        }
        
        CGSize newSize = CGSizeMake(self.size.width / ratio, self.size.height / ratio);
        
//        DDLogInfo(@"%@ outputSize: %@", NSStringFromSelector(_cmd), NSStringFromCGSize(newSize));
        
        UIGraphicsBeginImageContextWithOptions(newSize, NO, 0);
        [self drawInRect:CGRectMake(0, 0, newSize.width, newSize.height)];
        UIImage *newImage = UIGraphicsGetImageFromCurrentImageContext();
        UIGraphicsEndImageContext();
        
        return newImage;
    }
    
    return self;
}

- (UIImage *)resizeImageWithScaledToSize:(CGSize)newSize {
    UIGraphicsBeginImageContextWithOptions(newSize, NO, 0);
    [self drawInRect:CGRectMake(0, 0, newSize.width, newSize.height)];
    UIImage *newImage = UIGraphicsGetImageFromCurrentImageContext();
    UIGraphicsEndImageContext();
    
    return newImage;
}

- (UIImage *)setResizeImageWithSize:(NSInteger)size {
    CGSize imageSize = self.size;
    if (imageSize.width > size || imageSize.height > size) {
        CGFloat scaleRatio = MIN( size / imageSize.width , size / imageSize.height);
        CGSize scaledSize = {imageSize.width * scaleRatio, imageSize.height * scaleRatio};
//        DDLogDebug(@"Size: %@", NSStringFromCGSize(scaledSize));
        UIGraphicsBeginImageContextWithOptions(scaledSize, NO, 0);
        [self drawInRect:CGRectMake(0, 0, scaledSize.width, scaledSize.height)];
        UIImage *newImage = UIGraphicsGetImageFromCurrentImageContext();
        UIGraphicsEndImageContext();
        return newImage;
    }
    return self;
}

- (UIImage *)waterMarkWithImage:(UIImage *)waterMark {
    
    waterMark = [waterMark resizeImageWithScaledToSize:CGSizeMake(800, 200)];
    UIImage *watermarkedImage = nil;
    UIGraphicsBeginImageContext(self.size);
    
    [self drawAtPoint: CGPointZero];
    [waterMark drawInRect:CGRectMake(self.size.width / 2 - waterMark.size.width / 2, self.size.height / 2 - waterMark.size.height / 2, waterMark.size.width, waterMark.size.height)];
    
    watermarkedImage = UIGraphicsGetImageFromCurrentImageContext();
    UIGraphicsEndImageContext();
    
    return watermarkedImage;
}

使用：

self.checkedNormalImage = [[UIImage imageNamed:@"btn_untick"] resizeImageToDimension:CGSizeMake(16, 16)];

  这样可以适配大小