compress_news_images and png images?

[snarkophilus]

Would it be much work to make compress_news_images work for PNG files too? One news site I use has some 3-10MB PNG images that would be nice to resize like is already possible for JPG files.

I see that scale_image() in src/calibre/utils/img.py looks like it can deal with PNG files, but rescale_image() in src/calibre/web/fetch/simple.py only tries to rescale JPEG/JPG files. It looks like we convert anything that isn't PNG/JPEG/JPEG to these formats, so could it be as simple as changing the rescale check from

                    if self.compress_news_images and itype in {'jpg','jpeg'}:

to

                    if self.compress_news_images:

?

(I know enough python to be dangerous, but probably not be useful!)

[kovidgoyal]

Look at the implementationof rescale_images() in fetch/utils.py you will see it works by using a compression_quality parameter which is decreased in steps to get the desired file size. There is no such parameter in PNG since it is a lossless format.

[snarkophilus]

Ah, of course! I forgot that PNG was lossless.

I grabbed a couple of these large PNGs and using ImageMagick's convert program and could shrink these to a much smaller files that are still more than usable for a news recipe. These are converted with convert -resize 100000@ :

img15.png PNG 1975x465 1975x465+0+0 8-bit sRGB 631111B 0.000u 0:00.000
img15_small.png PNG 651x153 651x153+0+0 8-bit sRGB 70669B 0.000u 0:00.000
img1_u1.png PNG 3840x2160 3840x2160+0+0 8-bit sRGB 6.93234MiB 0.000u 0:00.000
img1_u1_small.png PNG 421x237 421x237+0+0 8-bit sRGB 168503B 0.000u 0:00.000

-rw-rw-rw-  1 simonb   631111 Aug  1 06:01 img15.png
-rw-r--r--  1 simonb    70669 Aug  4 00:38 img15_small.png
-rw-rw-rw-  1 simonb  7269085 Aug  1 06:01 img1_u1.png
-rw-r--r--  1 simonb   168503 Aug  4 00:38 img1_u1_small.png

I see that calibre used to have a dependancy on ImageMagick but no longer does. Do we have any other options for doing something like what the convert program does?

[kovidgoyal]

You can resize images as much as you like, using the function in utils/img.py to load a QImage and then using the QImage::scaled() function.

[snarkophilus]

Ok, thanks. I'll have a look and see if I can hook that into a recipe.

[MasterPlexus]

Originally Posted by snarkophilus

Ok, thanks. I'll have a look and see if I can hook that into a recipe.

Hi. Did you succeed? I'm also interested to shrink png's, as my magazine is quite too big with them

A short reusable example would be great!

[epubli]

Here is a short code example to resize PNG images within a news recipe:

from calibre.utils.magick import Image

...
    def postprocess_html(self, soup, first):
        maxwidth=800
        # Shrink large PNG images
        for tag in soup.findAll(lambda tag: tag.name.lower()=='img' and tag.has_key('src')):
          iurl = tag['src']
          if iurl.upper().endswith('PNG'):
              img = Image()
              img.open(iurl)
              width, height = img.size
              if( width > maxwidth ):
                factor=maxwidth/width
                img.size=(int(width/16 * factor)*16, int(height/16 * factor)*16)
                img.save(iurl)
        return soup