压缩UIImage

Question

我需要帮助调整UIImage的大小。

例如：我在UICollection视图中显示很多图像，但这些图像的大小为2到4 MB。我需要压缩或调整这些图像的大小。

我发现了这个：How to compress/resize image on iPhone OS SDK before uploading to a server?但我不明白如何实现它。

Answer 1

不确定是否要调整大小或压缩，或两者兼而有之。

下面是压缩的代码：

通过两个简单的步骤使用JPEG Compression：

1）将UIImage转换为NSData

UIImage *rainyImage =[UImage imageNamed:@"rainy.jpg"];
NSData *imgData= UIImageJPEGRepresentation(rainyImage,0.1 /*compressionQuality*/);

这是有损压缩，图像尺寸减小。

2）转换回UIImage;

UIImage *image=[UIImage imageWithData:imgData];

对于缩放，您可以使用Matteo Gobbi提供的答案。但缩放可能不是最好的选择。您更愿意通过压缩获得实际图像的缩略图，因为缩放可能会使您的图像在视网膜显示设备上看起来很糟糕。

Answer 2

我写了这个函数来缩放图像：

- (UIImage *)scaleImage:(UIImage *)image toSize:(CGSize)newSize {
    CGSize actSize = image.size;
    float scale = actSize.width/actSize.height;

    if (scale < 1) {
        newSize.height = newSize.width/scale;
    } else {
        newSize.width = newSize.height*scale;
    }


    UIGraphicsBeginImageContext(newSize);
    [image drawInRect:CGRectMake(0, 0, newSize.width, newSize.height)];
    UIImage* newImage = UIGraphicsGetImageFromCurrentImageContext();
    UIGraphicsEndImageContext();

    return newImage;
}

使用很简单，例如：

[self scaleImage:yourUIImage toSize:CGMakeSize(300,300)];

Answer 3

lowResImage = [UIImage imageWithData:UIImageJPEGRepresentation(highResImage, quality)];

Answer 4

 -(UIImage *) resizeImage:(UIImage *)orginalImage resizeSize:(CGSize)size
 {
CGFloat actualHeight = orginalImage.size.height;
CGFloat actualWidth = orginalImage.size.width;

float oldRatio = actualWidth/actualHeight;
float newRatio = size.width/size.height;
if(oldRatio < newRatio)
{
    oldRatio = size.height/actualHeight;
    actualWidth = oldRatio * actualWidth;
    actualHeight = size.height;
}
else
{
    oldRatio = size.width/actualWidth;
    actualHeight = oldRatio * actualHeight;
    actualWidth = size.width;
}

CGRect rect = CGRectMake(0.0,0.0,actualWidth,actualHeight);
UIGraphicsBeginImageContext(rect.size);
[orginalImage drawInRect:rect];
orginalImage = UIGraphicsGetImageFromCurrentImageContext();
UIGraphicsEndImageContext();
return orginalImage;
 }
      //this image you can add it to imageview.....