python在将(pdf)转换为jpeg时设置最大文件大小

For subsequent processing purposes, in python I am converting a multi-page PDF (f) into JPEGs (temp?.jpg):

为了后续的处理目的，在python中，我正在将一个多页的PDF (f)转换为jpeg (temp?.jpg):

import os
from wand.image import Image as wimage

with wimage(filename=f,resolution=300) as img:
    for i in range(len(img.sequence)):
        ftemp=os.path.abspath('temp%i.jpg'%i)
        img_to_save=wimage(img.sequence[i])
        img_to_save.compression_quality = 100
        img_to_save.format='jpeg'
        img_to_save.save(filename=ftemp)

I am using wand because of its ability to sequence the PDF pages, but am open to PIL etc.

我之所以使用wand，是因为它可以对PDF页面进行排序，但对PIL等软件开放。

I need the resolution and compression_quality to be as high as possible, but I want each JPEG to be no larger than (say) 300 kb in size.

我需要尽可能高的分辨率和compression_quality，但是我希望每个JPEG的大小不大于(比方说)300kb。

How can I set a limit to the size of the JPEG file?

如何限制JPEG文件的大小?

On the command line I would just do (see https://*.com/a/11920384/1021819):

在命令行上，我只需这样做(参见https://*.com/a/11920384/1021819):

convert original.jpeg -define jpeg:extent=300kb -scale 50% output.jpg

Thanks!

谢谢!

1 个解决方案

#1

The wand library has wand.image.OptionDict for managing -define attributes, but unfortunately all options are locked by wand.image.Option frozenset. IMHO, this renders the whole feature as unusable.

魔棒库有wand.image。用于管理-define属性的选项，但不幸的是所有选项都被wand.image锁定。选择frozenset。IMHO，这使整个特性变得不可用。

Luckily, you can create a quick sub-class to handle this via the wand.api.

幸运的是，您可以通过wand.api创建一个快速子类来处理这个问题。

import os
from wand.image import Image
from wand.api import library
from wand.compat import binary

class wimage(Image):
    def myDefine(self, key, value):
        """ Skip over wand.image.Image.option """
        return library.MagickSetOption(self.wand, binary(key), binary(value))


with wimage(filename=f, resolution=300) as img:
    for i in range(len(img.sequence)):
        ftemp=os.path.abspath('temp%i.jpg'%i)
        with wimage(img.sequence[i]) as img_to_save:
            img_to_save.myDefine('jpeg:extent', '300kb')
            img_to_save.compression_quality = 100
            img_to_save.format='jpeg'
            img_to_save.save(filename=ftemp)

In the near future. The wand.image.Option would be deprecated, and you could simply call img_to_save.options['jpeg:extent'] = '300kb'.

在不久的将来。wand.image。选项将被废弃，您可以简单地调用img_to_save。选择[' jpeg:程度上']= 300 kb。

#1