Recipe - Indian times and new function! PNG Cover

[VoHegg]

Hi, kovid, hi guys,

here is a new recipe. I only create it to show how i insert PNG coverfiles into my RSS feeds.
I found out that only jpg/jpeg files are shown as calibre covers. But mostly i got PNG files with alpha channel for this. (as i search on google-pictures for e.g. indian times ;-)
So i wrote a python function to convert this for me. May it is possible to add this functionality into the code? If not , this works like charm. Try it.

#!/usr/bin/env python2
# vim:fileencoding=utf-8
from __future__ import unicode_literals, division, absolute_import, print_function
from calibre.web.feeds.news import BasicNewsRecipe

# some modification to get png as coverurl
from PIL import Image
from urllib2 import urlopen
from tempfile import mkdtemp
    
# (my) calibre only allow jpeg files as cover.
# mostly i got fine png files  so i convert them
def png_to_jpg(url):
    # e.g. url is 'http:\wiki.com\myfinecover.png'
    # first we take the extension of the url if we got one
    ext = url.rsplit('.', 1)[-1]
    # now ext = png 
    # now we check if png match. May later we want other extension to? like svg ...?
    if ext.upper() in ('PNG'):
        # load the png url file to memory
        im = Image.open(urlopen(url))
        # if our png file has a alpha channel - remember jpg could not have one
        if im.mode in ('RGBA', 'LA'):
            # if we got alpha pictures, we create a backgound as a RGB Colored image with size of our original
            bg = Image.new(im.mode[:-1], im.size, (255,255,255))
            # and past the loaded image in front of the background
            bg.paste(im,im.split()[-1])
            # rewrite our loaded image with the new one
            im = bg
        # next to create a temporary directory and add the jpg extension . Finally we get a temp jpg filename
        tmp = mkdtemp()+ '.jpg'
        # save our picture as a jpg file
        # variable tmp holds the filename
        im.convert('RGB').save(tmp,"JPEG") #this converts png image as jpeg
    else: # no png extension, so we pass the url to the output
        tmp = url
    return tmp    
   
class AdvancedUserRecipe1583667870(BasicNewsRecipe):
    title			= 'The Times of India'
    description		= 'just a little demo to show the PNG cover function'
    __author__ 		= 'vohe'
    publisher 		= 'i guess: The Times Group'

    use_embedded_content = False
    language = 'en'
    rescale_images = True
    remove_empty_feeds = True
    timeout = 5
    no_stylesheets = True
    oldest_article = 2
    max_articles_per_feed = 200
    auto_cleanup   = True
    
    cover_url = png_to_jpg('https://upload.wikimedia.org/wikipedia/en/thumb/8/82/The_Times_Group.svg/1200px-The_Times_Group.svg.png')
    
    feeds          = [
        ('Times of india', 'https://timesofindia.indiatimes.com/rssfeeds/-2128936835.cms'),
    ]

[kovidgoyal]

calibre will automatically convert images to jpeg as needed.