iOS--图片压缩

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;
}