图片压缩

1. 
   压缩成指定大小
2. 
   
3. - (UIImage *)scaleToSize:(UIImage *)img size:(CGSize)size{    
4.     // 创建一个bitmap的context    
5.     // 并把它设置成为当前正在使用的context    
6.     UIGraphicsBeginImageContext(size);    
7.     // 绘制改变大小的图片    
8.     [img drawInRect:CGRectMake(0,0, size.width, size.height)];    
9.     // 从当前context中创建一个改变大小后的图片    
10.     UIImage* scaledImage =UIGraphicsGetImageFromCurrentImageContext();    
11.     // 使当前的context出堆栈    
12.     UIGraphicsEndImageContext();    
13.     //返回新的改变大小后的图片    
14.     return scaledImage;    
15. }  

等比例压缩

-(UIImage *) imageCompressForSize:(UIImage *)sourceImage targetSize:(CGSize)size{

    UIImage *newImage = nil;

    CGSize imageSize = sourceImage.size;

    CGFloat width = imageSize.width;

    CGFloat height = imageSize.height;

    CGFloat targetWidth = size.width;

    CGFloat targetHeight = size.height;

    CGFloat scaleFactor = 0.0;

    CGFloat scaledWidth = targetWidth;

    CGFloat scaledHeight = targetHeight;

    CGPoint thumbnailPoint = CGPointMake(0.0, 0.0);

    if(CGSizeEqualToSize(imageSize, size) == NO){

        CGFloat widthFactor = targetWidth / width;

        CGFloat heightFactor = targetHeight / height;

        if(widthFactor > heightFactor){

            scaleFactor = widthFactor;

        }

        else{

            scaleFactor = heightFactor;

        }

        scaledWidth = width * scaleFactor;

        scaledHeight = height * scaleFactor;

        if(widthFactor > heightFactor){

            thumbnailPoint.y = (targetHeight - scaledHeight) * 0.5;

        }else if(widthFactor < heightFactor){

            thumbnailPoint.x = (targetWidth - scaledWidth) * 0.5;

        }

    }

    UIGraphicsBeginImageContext(size);

    CGRect thumbnailRect = CGRectZero;

    thumbnailRect.origin = thumbnailPoint;

    thumbnailRect.size.width = scaledWidth;

    thumbnailRect.size.height = scaledHeight;

    [sourceImage drawInRect:thumbnailRect];

    newImage = UIGraphicsGetImageFromCurrentImageContext();

    

    if(newImage == nil){

        NSLog(@"scale image fail");

    }

    UIGraphicsEndImageContext();

    

    return newImage;

    

}

-(UIImage *) imageCompressForWidth:(UIImage *)sourceImage targetWidth:(CGFloat)defineWidth{

    UIImage *newImage = nil;

    CGSize imageSize = sourceImage.size;

    CGFloat width = imageSize.width;

    CGFloat height = imageSize.height;

    CGFloat targetWidth = defineWidth;

    CGFloat targetHeight = height / (width / targetWidth);

    CGSize size = CGSizeMake(targetWidth, targetHeight);

    CGFloat scaleFactor = 0.0;

    CGFloat scaledWidth = targetWidth;

    CGFloat scaledHeight = targetHeight;

    CGPoint thumbnailPoint = CGPointMake(0.0, 0.0);

    if(CGSizeEqualToSize(imageSize, size) == NO){

        CGFloat widthFactor = targetWidth / width;

        CGFloat heightFactor = targetHeight / height;

        if(widthFactor > heightFactor){

            scaleFactor = widthFactor;

        }

        else{

            scaleFactor = heightFactor;

        }

        scaledWidth = width * scaleFactor;

        scaledHeight = height * scaleFactor;

        if(widthFactor > heightFactor){

            thumbnailPoint.y = (targetHeight - scaledHeight) * 0.5;

        }else if(widthFactor < heightFactor){

            thumbnailPoint.x = (targetWidth - scaledWidth) * 0.5;

        }

    }

    UIGraphicsBeginImageContext(size);

    CGRect thumbnailRect = CGRectZero;

    thumbnailRect.origin = thumbnailPoint;

    thumbnailRect.size.width = scaledWidth;

    thumbnailRect.size.height = scaledHeight;

    [sourceImage drawInRect:thumbnailRect];

    newImage = UIGraphicsGetImageFromCurrentImageContext();

    if(newImage == nil){

        NSLog(@"scale image fail");

    }

    UIGraphicsEndImageContext();

    return newImage;

}