原文链接：http://www.jianshu.com/p/fb6a072fba47
最近做的项目中需要上传头像，发表内容的时候也要涉及到图片上传，我直接用的原图上传，但是由于公司网络差，原图太大，老是加载好久好久，所以需要把原图裁剪或者修改分辨率之后再上传，找了好久，做了很多尝试才解决问题，下面记录一下，以便帮助自己查找，也希望能帮助其他人。
我们一般图片上传最好使用UIImageJPEGRepresentation(image, 0.1)这个方法先把图片处理一下，其实这个方法把图片压缩之后，图片大小会小很多（小多少待会再讲），但是在app上人眼的感觉差不多，我对图片的处理如下：
从相册拿到图片后，先经过方法修改图片的大小，也就是分辨率，方法如下：
- - (UIImage *)scaleImage:(UIImage *)image toSize:(CGSize)size
- {
- UIGraphicsBeginImageContextWithOptions(size,NO,0.0);
- [image drawInRect:CGRectMake(0, 0, size.width, size.height)];
- UIImage *scaledImage = UIGraphicsGetImageFromCurrentImageContext();
- UIGraphicsEndImageContext();
- return scaledImage;
- }
因为我是要上传头像，所以我把图片的size设置为(128,128)，这里我在模拟器中截取到了一个320*320的图片，然后经过这个方法压缩后得到的图片是20.3KB，然后我在上传之前又用UIImageJPEGRepresentation(image, 0.05)把图片品质压缩了一下，图片的大小变成了1.5KB左右，这样的小图，在app上加载起来快急了，之前那个七八十KB的图片经常都加载不出来呢，现在OK了~。
总结：1、用 - (UIImage *)scaleImage:(UIImage *)image toSize:(CGSize)size 修改图片的分辨率；
2、用 UIImageJPEGRepresentation(image,0.1)这个方法来压缩图片品质。
我们可以在不减小图片的分辨率（质量可以适当减小）的情况下，显著减小图片的大小
float kCompressionQuality = 0.3; // 具体大小自己调NSData *photo = UIImageJPEGRepresentation(UIImage, kCompressionQuality);
上面方法等价于下面: 压缩图片质量
+(UIImage *)reduceImage:(UIImage *)image percent:(float)percent{ NSData *imageData = UIImageJPEGRepresentation(image, percent); UIImage *newImage = [UIImage imageWithData:imageData]; return newImage; } //将图片压缩到指定比例
-(UIImage *)scaleToSize:(UIImage *)aImage size:(CGSize)size{ //创建context,并将其设置为正在使用的context UIGraphicsBeginImageContext(size); //绘制出图片(大小已经改变) [aImage drawInRect:CGRectMake(0, 0, size.width, size.height)]; //获取改变大小之后的图片 UIImage *newImage = UIGraphicsGetImageFromCurrentImageContext(); //context出栈 UIGraphicsEndImageContext(); return newImage; //返回获得的图片 } 等比例压缩
//等比例压缩-(UIImage *)oldImage:(UIImage *)oldImage toSize:(CGSize)size{ UIImage *newImage = nil;//新照片对象 CGSize theSize = oldImage.size;//压缩前图片size CGFloat width = theSize.width; //压缩前图片width CGFloat height = theSize.height;//压缩前图片height CGFloat newWidth = size.width; //压缩后图片width CGFloat newHeight = size.height;//压缩后图片height CGFloat scaleFactor = 0.0;//初值 CGFloat toWidth = newWidth;//压缩后图片width CGFloat toHeight = newHeight;//压缩后图片height CGPoint thumnailPoint = CGPointMake(0.0, 0.0);//给初值 if (CGSizeEqualToSize(theSize, size) == NO) { //判断是不是已经满足 theSize = size 要求 CGFloat widthFac = newWidth/width; CGFloat heithrFac = newHeight/height; if (widthFac > heithrFac) { scaleFactor = widthFac; }else { scaleFactor = heithrFac; } //不满足做等比例缩小处理 toWidth = width *scaleFactor; toHeight = height *scaleFactor; if (widthFac > heithrFac) { thumnailPoint.y = (newHeight - toHeight)* 0.5; }else if (widthFac < heithrFac){ thumnailPoint.x = (newWidth - toWidth)* 0.5; } } //创建context,并将其设置为正在使用的context UIGraphicsBeginImageContext(size); CGRect thumbnailRect = CGRectZero; thumbnailRect.origin = thumnailPoint; thumbnailRect.size.width = toWidth; thumbnailRect.size.height = toHeight; //绘制出图片(大小已经改变) [oldImage drawInRect:thumbnailRect]; newImage = UIGraphicsGetImageFromCurrentImageContext(); //结果判断 if (newImage == nil) { [NSException exceptionWithName:@"提示" reason:@"Error:image scale fail" userInfo:nil]; } 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; } 图片的压缩其实是俩概念，
1、是 “压” 文件体积变小，但是像素数不变，长宽尺寸不变，那么质量可能下降，2、是 “缩” 文件的尺寸变小，也就是像素数减少。长宽尺寸变小，文件体积同样会减小。这个 UIImageJPEGRepresentation(image, 0.0)，是1的功能。这个 [sourceImage drawInRect:CGRectMake(0,0,targetWidth, targetHeight)] 是2的功能。所以，这俩你得结合使用来满足需求，不然你一味的用1，导致，图片模糊的不行，但是尺寸还是很大。我们还可以对图片进行部分截取
-(UIImage*)getSubImage:(CGRect)rect{ CGImageRefsubImageRef =CGImageCreateWithImageInRect(self.CGImage,rect); CGRectsmallBounds =CGRectMake(0,0, CGImageGetWidth(subImageRef),CGImageGetHeight(subImageRef)); UIGraphicsBeginImageContext(smallBounds.size); CGContextRefcontext =UIGraphicsGetCurrentContext(); CGContextDrawImage(context,smallBounds,subImageRef); UIImage*smallImage =[UIImage imageWithCGImage:subImageRef]; UIGraphicsEndImageContext(); returnsmallImage; } //--------------截取部分图片到指定位置-------------------------
图片(UIImage*)img要截取的起始坐标sx:(int)sx1 sy:(int)sy1要截取的长度和宽度sw:(int)sw1 sh:(int)sh1 最终要显示的坐标desx:(int)desx1 desy:(int)desy1 -(UIImage*)objectiveDrawRegion:(UIImage*)img sx:(int)sx1 sy:(int)sy1sw:(int)sw1 sh:(int)sh1 desx:(int)desx1 desy:(int)desy1{ [selfsaveImage:imgname:@"objectiveDrawRegion1.png"]; //创建图片缓冲 void*imageDataRegion=malloc(screenWidth*screenHeight*32); CGColorSpaceRefiColorSpaceRegion=CGColorSpaceCreateDeviceRGB(); CGContextRefiDeviceRegion=CGBitmapContextCreate(imageDataRegion,screenWidth,screenHeight,8,4*screenWidth,iColorSpaceRegion,kCGImageAlphaPremultipliedLast); //剪切区域 CGRectclipRegion=CGRectMake(sx1,sy1,sw1,sh1); CGContextClipToRect(iDeviceRegion,clipRegion); CGFloatwidthf=img.size.width; CGFloatheightf=img.size.height; CGRect cg=CGRectMake(0.0,0.0, widthf, heightf); //画底图 CGContextDrawImage(iDeviceRegion,cg,img.CGImage); //将缓冲形成图片 CGImageRefioffRegion=CGBitmapContextCreateImage(iDeviceRegion); CGRect cg1=CGRectMake(desx1,desy1, sw1, sh1); UIImage *ui=[UIImageimageWithCGImage:ioffRegion]; CGContextDrawImage(当前context,cg1,ui.CGImage); //清除缓冲 CGColorSpaceRelease(iColorSpaceRegion); CGContextRelease(iDeviceRegion); CGImageRelease(ioffRegion); free(imageDataRegion); // iDeviceRegion=NULL; // imageDataRegion=0; returnui; } 参考：http://www.henishuo.com/ios-image-compressed/