iOS 圖片壓縮 和等比壓縮 指定縮放比例壓縮

- (UIImage *)scaleToSize:(UIImage *)img size:(CGSize)size{    
    // 創建一個bitmap的context    
    // 并把它設置成為當前正在使用的context        UIGraphicsBeginImageContext(size);    
    // 繪制改變大小的圖片    
    [img drawInRect:CGRectMake(0,0, size.width, size.height)];    
    // 從當前context中創建一個改變大小后的圖片    
    UIImage* scaledImage =UIGraphicsGetImageFromCurrentImageContext();    
    // 使當前的context出堆棧        UIGraphicsEndImageContext();    
    //返回新的改變大小后的圖片    
    return scaledImage;    
}

等比例壓縮
-(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;

}</pre> 


 //指定縮放比例壓縮
  NSData *thumbImageData = UIImageJPEGRepresentation([UIImage imageWithData:logoData], 0.5);