iOS压缩图片处理

1.压缩图片质量(图片体积减小,像素不变)

两种读取图片数据的简单方法:

(1).UIImageJPEGRepresentation函数需要两个参数:图片的引用和压缩系数,压缩体积不是随压缩系数比例变化的。

(2).UIImagePNGRepresentation只需要图片引用作为参数。

注意:

UIImagePNGRepresentation(image) 要比UIImageJPEGRepresentation(image, 1.0) 返回的图片数据量大很多

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。

+(UIImage *)reduceImage:(UIImage *)image percent:(float)percent

{

   NSData *imageData =UIImageJPEGRepresentation(image, percent);

   UIImage *newImage = [UIImage imageWithData:imageData];

   return newImage;

}

2.图片压缩到指定尺寸

+ (UIImage *) scaleImage:(UIImage *) image withNewSize:(CGSize) newSize

{

    UIGraphicsBeginImageContext(newSize);

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

    UIImage *newImage =UIGraphicsGetImageFromCurrentImageContext();

    UIGraphicsEndImageContext();

    return newImage;

}

3.压缩到指定尺寸等比例压缩

-(UIImage *) imageCompressForSize:(UIImage *)sourceImage targetSize:(CGSize)size{

    UIImage *newImage = nil;

    CGSize imageSize = sourceImage.size;

    CGFloat width = imageSize.width;

    CGFloat height = imageSize.height;

    CGFloat targetWidth = size.width;

    CGFloat targetHeight = size.height;

    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;

        }elseif(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;

}

-(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;

     }elseif(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;

}