Image conversion changed btwn 6.14.1 and 7.12.0

[Quoth]

You can use a compromise size for all ebooks and a different size for POD, or even the same for them all.

I'd not use actual Adobe Photoshop now as it's too expensive. There are many good enough free tools. Not used Photoshop for years.

These are clearly what are required. And again these are based on the output that I was getting from Calibre 6.14.1 and which produce an output that looks good on the specified platforms.

No, they are not. As these are larger images a percent is needed. Kobo has not just 300 dpi, but 6" and 6.8" screens with lower DPI.

Apple has phones and tablets.

We distribute the same content (same file inc images) to Amazon, Apple, Barnes & Nobel, Google Playbooks, Kobo, Tolino etc.

I used to use Paint Shop Pro7 and still MS Word after Photoshop, then changed to The GIMP (go first to settings and make the GUI, toolbox and Icon theme sane) and LO Writer. This was still on XP. I used Win7 for a while and then changed to Linux Mint with Mate Desktop.

I had to export all my PSP7 files as Photoshop for The GIMP to read them.

There is nothing wrong with Calibre. It's brilliant for converting docx to epub2 and leaving the images exactly as they are. Then I do some CSS edit (with preview).
The css sections with auto all had pt on the Calibre conversion from docx.

.calibre1 {
  height: auto;
  width: 66.67%;
}
.calibre2 {
  height: 45pt;
  width: 70.3pt;
}
.calibre3 {
  text-decoration: none;
}
.calibre4 {
  height: 43.1pt;
  width: 43.1pt;
}
.calibre5 {
  display: block;
}
.calibre6 {
  height: auto;
  width: 75%;
}
.calibre7 {
  height: auto;
  width: 20%;
}
.calibre8 {
  font-style: italic;
}
.calibre9 {
  height: auto;
  width: 80%;
}
.calibre10 {
  height: auto;
  width: 50%;
}
.calibre11 {
  height: auto;
  width: 66.67%;
}
.text_ {
  color: #000080;
  text-decoration: underline solid;
}

Some small images are left as pt, because


Text and margins and padding can be in pt or em. By default 12 pt = 1em, though kepub may not use that for margins.

A px is not a pixel. A 1 px line is "the finest line to render without anti-aliasing" (may not be quite true).
Images should use px or % or auto, but pt may work well for small images. In this case 12pt = 16 px if the renderer doesn't scale images in pt. On some apps/ereaders the image is scalled with font if it's set in pt. It's never scaled if it's in px.

There is no pixel setting.

A body font is assumed to be 1em if not stated and the user can increase or decrease, but unlike zoom on PDF, everything reflows and margins, padding and line spacing change, assuming line spacing isn't set.
Never set line spacing for an ebook (that's for web pages and paper). The spacing is then set by font size and font metrics.

Never use cm, inch etc for anything, those are for paper.

Never use px for fonts, margins or padding. Use em, pt (12 pt = 1em) or % (100% = 1em).

Web pages don't work exactly the same. Calibre viewer and some other ereader apps are really web browsers using ebook-like rules, so sometimes behave differently to physical ereaders. Kindle AZW3 is much like epub2. The Kindle KFX and Kobo kepub handle text spacing and kerning a bit different and may allow image zoom.

We proof as epub2 and copy/paste wordprocessor content for epub into a new template for paper POD.

The epub3 can be similar to epub2, or be quite diifferent. Some of the epub3 features just mimic PDF and others mimic a multimedia framework.

I edit odt files with an extra docx only for Calibre. I used to interchange docx, but the others are all now using LO Writer instead of Word. Traditional publishers want docx. Self-publishing entirely uses epub2 (though other formats possible) for real ebooks (reflowable & no multimedia/interactive) and pdf for POD or fixed layout.

We don't deal with Apple (painful), Kobo, Barnes & Noble etc direct, but via Smashwords/Direct2Digital. Amazon and Google get separate uploads.

Amazon unfortunately has over 92% of English Language title sales world-wide and Google mysteriously tiny. We've had almost as many sales on non-Amazon (all combined) as Amazon and none on Google! So I suspect many are only uploading to Amazon.