压缩图片

压缩图片有两种, 一种是换尺寸, 一种是压缩质量

如果是jpeg可以直接

float kCompressionQuality = 0.3; // 具体大小自己调
NSData *photo = UIImageJPEGRepresentation(UIImage, kCompressionQuality);

上面等价于下面, 适用于格式为png的

+(UIImage *)reduceImage:(UIImage *)image percent:(float)percent
{
    NSData *imageData = UIImageJPEGRepresentation(image, percent);
    UIImage *newImage = [UIImage imageWithData:imageData];
    return newImage;
}

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

-(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;
}

等比压缩

 -(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;
}

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;
}

感谢http://www.jianshu.com/p/fb6a072fba47?utm_campaign=hugo&utm_medium=reader_share&utm_content=note&utm_source=qq