压缩图片

最新推荐文章于 2024-10-30 11:22:33 发布

最新推荐文章于 2024-10-30 11:22:33 发布 · 100 阅读

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本文介绍了一个UIImage的分类扩展方法，用于实现图片的压缩功能。该方法包括UIImage的压缩、压缩质量的计算以及压缩后的数据导出等功能。通过设定最大像素值和最大数据长度限制，可以有效地减小图片尺寸。

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@interface UIImage (Compress)

- (UIImage *)compressedImage;

- (CGFloat)compressionQuality;

- (NSData *)compressedData;

- (NSData *)compressedData:(CGFloat)compressionQuality;

@end


#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