iOS中兩種壓縮圖片的方法
UIImageJPEGRepresentation. UIImagePNGRepresentation

JPEG圖片只支持白底且保存時(shí)是有損壓縮，占用空間較小，PNG可以支持透明背景且使用無(wú)損壓縮算法，但由于壓縮比高，所以占用空間跟JPEG沒(méi)有太大差別

執(zhí)行完之后會(huì)有一個(gè)最小值 即使系數(shù)為0.000001。所以需要改變圖片的大小

#pragma mark - 壓縮圖片
- (NSData *)compressOriginalImage:(UIImage *)image toMaxDataSizeKBytes:(CGFloat)size
{
    UIImage *OriginalImage = image;
    
    // 執(zhí)行這句代碼之后會(huì)有一個(gè)范圍 例如500m 會(huì)是 100m～500k
    NSData * data = UIImageJPEGRepresentation(image, 1.0);
    CGFloat dataKBytes = data.length/1000.0;
    CGFloat maxQuality = 0.9f;
    
    // 執(zhí)行while循環(huán) 如果第一次壓縮不會(huì)小雨100k 那么減小尺寸在重新開(kāi)始?jí)嚎s
    while (dataKBytes > size)
    {
        while (dataKBytes > size && maxQuality > 0.1f)
        {
            maxQuality = maxQuality - 0.1f;
            data = UIImageJPEGRepresentation(image, maxQuality);
            dataKBytes = data.length / 1000.0;
            if(dataKBytes <= size )
            {
                return data;
            }
        }
        OriginalImage =[self compressOriginalImage:OriginalImage toWidth:OriginalImage.size.width * 0.8];
        image = OriginalImage;
        data = UIImageJPEGRepresentation(image, 1.0);
        dataKBytes = data.length / 1000.0;
        maxQuality = 0.9f;
    }
    return data;
}

#pragma mark - 改變圖片的大小
-(UIImage *)compressOriginalImage:(UIImage *)image toWidth:(CGFloat)targetWidth
{
    CGSize imageSize = image.size;
    CGFloat Originalwidth = imageSize.width;
    CGFloat Originalheight = imageSize.height;
    CGFloat targetHeight = Originalheight / Originalwidth * targetWidth;
    UIGraphicsBeginImageContext(CGSizeMake(targetWidth, targetHeight));
    [image drawInRect:CGRectMake(0,0,targetWidth,  targetHeight)];
    UIImage* newImage = UIGraphicsGetImageFromCurrentImageContext();
    UIGraphicsEndImageContext();
    return newImage;
}