如何在python中使用wand优化图像大小

Question

我想使用魔杖调整大小并优化png和jpg图像大小.

使用PIL,如果指定优化选项,我可以以大约3倍的大小保存相同的图像.

with open(filename, 'rb') as f:
    pimage = PImage.open(f)
    resized_pimage = pimage.resize((scaled_width, scaled_height), PImage.ANTIALIAS)            bytes_buffer = io.BytesIO()
    resized_pimage.save(bytes_buffer, format="PNG", optimize=True)

但是,我不确定Wand的等效选项是什么:

with default_storage.open(filename, 'rb') as f:
    img = WImage(file=f)
    img.resize(width=scaled_width, height=scaled_height, filter='gaussian')
    with WImage(width=scaled_width, height=scaled_height) as png:
        png.composite(img, top=0, left=0)
        png.format = 'png'
        bytes_buffer = io.BytesIO()
        png.save(file=bytes_buffer)

我读了关于ImageMagic图像优化几篇文章(例如http://www.smashingmagazine.com/2015/06/efficient-image-resizing-with-imagemagick/),但我怎么能在棒做这些(不是很明显我是Wand或PIL的完全新手.

任何帮助/指针将不胜感激.

Answer 1

更新答案

使用魔杖设置优化将需要一些额外的 MagickWand 库扩展/配置。这是因为quality需要在wand数据结构上设置属性，而不是图像的实例。使困惑？我是。幸运的是，Python 的 Wand 库让这一切变得简单。请尝试以下操作。

# Require wand's API library and basic ctypes
from wand.api import library
from ctypes import c_void_p, c_size_t

# Tell Python's wand library about the MagickWand Compression Quality (not Image's Compression Quality)
library.MagickSetCompressionQuality.argtypes = [c_void_p, c_size_t]

# Do work as before
from wand.image import Image

with Image(filename=filename) as img:
    img.resize(width=scaled_width, height=scaled_hight)
    # Set the optimization level through the linked resources of 
    # the image instance. (i.e. `wand.image.Image.wand`)
    library.MagickSetCompressionQuality(img.wand, 75)
    img.save(filename=output_destination)

原答案

png格式有多种“优化”类型，但我的印象是您正在寻求一种减小图像大小的方法。

我相信wand.Image.compression_quality这就是你要找的。

# Require wand's API library and basic ctypes
from wand.api import library
from ctypes import c_void_p, c_size_t

# Tell Python's wand library about the MagickWand Compression Quality (not Image's Compression Quality)
library.MagickSetCompressionQuality.argtypes = [c_void_p, c_size_t]

# Do work as before
from wand.image import Image

with Image(filename=filename) as img:
    img.resize(width=scaled_width, height=scaled_hight)
    # Set the optimization level through the linked resources of 
    # the image instance. (i.e. `wand.image.Image.wand`)
    library.MagickSetCompressionQuality(img.wand, 75)
    img.save(filename=output_destination)

以上不会像您期望的JPEG格式那样将质量降低到 75% ，但会指示使用哪个 PNG 压缩库/算法/过滤器。请参阅PNG 压缩和更好的 PNG 压缩示例。

from wand.image import Image

with Image(filename=filename) as img:
    img.resize(width=scaled_width, height=scaled_hight)
    img.compression_quality = 75
    img.save(filename=output_destination)

因此，将质量设置为75将7在执行adaptive过滤器后使用 zlib 级别进行压缩。请注意，这只是级别和过滤器，而不是优化策略。可以使用 CLI 选项设置优化策略，-define png:compression-strategy=zs但是wand尚未实现图像伪影方法。