setImageCompressionQuality 与 setCompressionQuality 之间有什么区别 - Imagick

我在Imagick中找到了两种设置图像压缩质量的方法

A）设置图像压缩质量

B ) 设置压缩质量

所以我想知道哪一个是最好的以及为什么在以下条件下

我读到了setCompressionQuality方法仅适用于新图像（？）

我正在尝试压缩文件 jpeg/png

$im = new Imagick();

$im->readImage($file); // path/to/file
$im->setImageCompressionQuality($quality); // 90,80,70 e.g.

$im->writeImage($file);

方法setImageCompressionQuality设置当前图像的压缩质量。该方法是一个包装器MagickWand's MagickSetImageCompressionQuality功能。源代码 https://github.com/ImageMagick/ImageMagick/blob/master/MagickWand/magick-image.c#L9448 is:

WandExport MagickBooleanType MagickSetImageCompressionQuality(MagickWand *wand,
  const size_t quality)
{
  assert(wand != (MagickWand *) NULL);
  assert(wand->signature == MagickWandSignature);
  if (wand->debug != MagickFalse)
    (void) LogMagickEvent(WandEvent,GetMagickModule(),"%s",wand->name);
  if (wand->images == (Image *) NULL)
    ThrowWandException(WandError,"ContainsNoImages",wand->name);

  //This line sets the quality for the instance 'images'  
  wand->images->quality=quality;
  return(MagickTrue);
}

方法setCompressionQuality设置整个对象的压缩质量。该方法是一个包装器MagickWand's MagickSetCompressionQuality功能。源代码 https://github.com/ImageMagick/ImageMagick/blob/master/MagickWand/magick-property.c#L1980 is:

WandExport MagickBooleanType MagickSetCompressionQuality(MagickWand *wand,
  const size_t quality)
{
  assert(wand != (MagickWand *) NULL);
  assert(wand->signature == MagickWandSignature);
  if (wand->debug != MagickFalse)
    (void) LogMagickEvent(WandEvent,GetMagickModule(),"%s",wand->name);

  //This line sets quality for the image_info struct instance.
  wand->image_info->quality=quality;
  return(MagickTrue);
}

The MagickWand结构体包含以下实例Image and ImageInfo结构体，source https://github.com/ImageMagick/ImageMagick/blob/master/MagickWand/magick-wand-private.h#L49:

struct _MagickWand
{
  ...

  Image
    *images;          /* The images in this wand - also the current image */

  ImageInfo
    *image_info;      /* Global settings used for images in Wand */
  ...
};

Both Image and ImageInfo https://github.com/ImageMagick/ImageMagick/blob/master/MagickCore/image.h#L151结构体持有一个size_t quality;数据成员。所以对于你的例子setImageCompressionQuality完全没问题。