Kindle Previewer 4.0.1 and size of kfx files

troubledMan · 10-02-2026, 12:16 PM

Hi all,

Does anyone know why the new (for me) version of Kindle Previewer (4.0.1; MacBook Air M1 16/512) produces larger kpf files than the previous version? I converted an ePub using the previous version and it was 2.5 Mb, whereas the same ePub converted using version 4 of Kindle Previewer is 3.7 Mb.

TIA

(It is kpf, not kfx, excuse me!)

jhowell · 10-02-2026, 09:12 PM

I haven’t compared file sizes with 4.0.1, but with the latest version 4.0.2 the KPF files I see are essentially the same size as those produced by version 3.107.

troubledMan · 10-03-2026, 04:26 AM

I’ve just installed version 4.0.2 and carried out some more tests. Depending on the ePub, the issue I encountered still persists: the resulting KPF file produced by version 4 is larger than the one obtained with KP version 3. But only in some cases: as I’m comparing text-only ePubs (excluding the cover), I imagine this difference must be related to the type of image used on the cover; I can’t think of any other explanation. In most cases, as you say, the size is the same. Thank you.

JSWolf · 10-03-2026, 03:26 PM

I've read somewhere that Amazon is switching to AVIF image format.

jhowell · 10-03-2026, 08:49 PM

Quote:

Originally Posted by JSWolf

I've read somewhere that Amazon is switching to AVIF image format.

As far as I know that is only on the website, not in Kindle formats.

JSWolf · 10-04-2026, 05:43 AM

Quote:

Originally Posted by jhowell

As far as I know that is only on the website, not in Kindle formats.

That's bit was left out.

10-02-2026, 12:16 PM	#1
troubledMan Connoisseur Posts: 66 Karma: 10 Join Date: Jun 2016 Location: In a city that is Real (for real) Device: KPW SE 12	Kindle Previewer 4.0.1 and size of kpf files Hi all, Does anyone know why the new (for me) version of Kindle Previewer (4.0.1; MacBook Air M1 16/512) produces larger kpf files than the previous version? I converted an ePub using the previous version and it was 2.5 Mb, whereas the same ePub converted using version 4 of Kindle Previewer is 3.7 Mb. TIA (It is kpf, not kfx, excuse me!) Last edited by troubledMan; 10-02-2026 at 12:49 PM. Reason: wrong file type

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10-02-2026, 09:12 PM	#2
jhowell Grand Sorcerer Posts: 7,435 Karma: 96111109 Join Date: Nov 2011 Location: Charlottesville, VA Device: Kindles	I haven’t compared file sizes with 4.0.1, but with the latest version 4.0.2 the KPF files I see are essentially the same size as those produced by version 3.107.

10-03-2026, 04:26 AM	#3
troubledMan Connoisseur Posts: 66 Karma: 10 Join Date: Jun 2016 Location: In a city that is Real (for real) Device: KPW SE 12	I’ve just installed version 4.0.2 and carried out some more tests. Depending on the ePub, the issue I encountered still persists: the resulting KPF file produced by version 4 is larger than the one obtained with KP version 3. But only in some cases: as I’m comparing text-only ePubs (excluding the cover), I imagine this difference must be related to the type of image used on the cover; I can’t think of any other explanation. In most cases, as you say, the size is the same. Thank you.

10-03-2026, 03:26 PM	#4
JSWolf Resident Curmudgeon Posts: 85,243 Karma: 154365101 Join Date: Nov 2006 Location: Roslindale, Massachusetts Device: Kobo Libra 2, Kobo Aura H2O, PRS-650, PRS-T1, nook STR, PW3	I've read somewhere that Amazon is switching to AVIF image format.