ios 压缩图片
转自 http://www.cnblogs.com/likwo/archive/2012/11/30/2796902.html
分两部分，1缩小图片大小2减弱图片质量
@1. 缩小图片大小
首先我们弄个catogory
//头文件
@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;
}
封装函数为：
+ (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.减弱图片质量
NSData *dataImg = UIImageJPEGRepresentation(img, 0.0001);
在Iphone上有两种读取图片数据的简单方法: UIImageJPEGRepresentation和UIImagePNGRepresentation. UIImageJPEGRepresentation函数需要两个参数:图片的引用和压缩系数.而UIImagePNGRepresentation只需要图片引用作为参数.通过在实际使用过程中,比较发现: UIImagePNGRepresentation(UIImage* image) 要比UIImageJPEGRepresentation(UIImage* image, 1.0) 返回的图片数据量大很多.譬如,同样是读取摄像头拍摄的同样景色的照片, UIImagePNGRepresentation()返回的数据量大小为199K ,而 UIImageJPEGRepresentation(UIImage* image, 1.0)返回的数据量大小只为140KB,比前者少了50多KB.如果对图片的清晰度要求不高,还可以通过设置 UIImageJPEGRepresentation函数的第二个参数,大幅度降低图片数据量.譬如,刚才拍摄的图片, 通过调用UIImageJPEGRepresentation(UIImage* image, 1.0)读取数据时,返回的数据大小为140KB,但更改压缩系数后,通过调用UIImageJPEGRepresentation(UIImage* image, 0.5)读取数据时,返回的数据大小只有11KB多,大大压缩了图片的数据量 ,而且从视角角度看,图片的质量并没有明显的降低.因此,在读取图片数据内容时,建议优先使用UIImageJPEGRepresentation,并可根据自己的实际使用场景,设置压缩系数,进一步降低图片数据量大小