UIImage壓縮2

分兩部分，1縮小圖片大小2減弱圖片質量
@1. 縮小圖片大小
首先我們弄個catogory
//頭文件
@interface UIImage (Compress)  
- (UIImage *)compressedImage;  
@end
//mm文件
#define MAX_IMAGEPIX 200.0          // max pix 200.0px  
#define MAX_IMAGEDATA_LEN 200.0   // 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;  
}

 

封裝函數為：

+ (UIImage*)imageWithImage:(UIImage*)image scaledToSize:(CGSize)newSize

{

    // Create a graphics image context

    UIGraphicsBeginImageContext(newSize);

    

    // Tell the old image to draw in this new context, with the desired

    // new size

    [image drawInRect:CGRectMake(0,0,newSize.width,newSize.height)];

    

    // Get the new image from the context

    UIImage* newImage = UIGraphicsGetImageFromCurrentImageContext();

    

    // End the context

    UIGraphicsEndImageContext();

    

    // Return the new image.

    return newImage;

}

@2.減弱圖片質量
NSData *dataImg = UIImageJPEGRepresentation(img, 0.0001);

 

在Iphone上有兩種讀取圖片數據的簡單方法: UIImageJPEGRepresentation和UIImagePNGRepresentation. UIImageJPEGRepresentation函數需要兩個參數:圖片的引用和壓縮系數.而UIImagePNGRepresentation只需要圖片引用作為參數.通過在實際使用過程中,比較發現: UIImagePNGRepresentation(UIImage* image) 要比UIImageJPEGRepresentation(UIImage* image, 1.0) 返回的圖片數據量大很多.譬如,同樣是讀取攝像頭拍攝的同樣景色的照片, UIImagePNGRepresentation()返回的數據量大小為199K ,而 UIImageJPEGRepresentation(UIImage* image, 1.0)返回的數據量大小只為140KB,比前者少了50多KB.如果對圖片的清晰度要求不高,還可以通過設置 UIImageJPEGRepresentation函數的第二個參數,大幅度降低圖片數據量.譬如,剛才拍攝的圖片, 通過調用UIImageJPEGRepresentation(UIImage* image, 1.0)讀取數據時,返回的數據大小為140KB,但更改壓縮系數后,通過調用UIImageJPEGRepresentation(UIImage* image, 0.5)讀取數據時,返回的數據大小只有11KB多,大大壓縮了圖片的數據量 ,而且從視角角度看,圖片的質量並沒有明顯的降低.因此,在讀取圖片數據內容時,建議優先使用UIImageJPEGRepresentation,並可根據自己的實際使用場景,設置壓縮系數,進一步降低圖片數據量大小