Bug 466653

Summary:	a5 300dpi resolution it not following iso standards
Product:	[Applications] krita	Reporter:	Isabelle <isabelle.axrup>
Component:	General	Assignee:	Krita Bugs <krita-bugs-null>
Status:	REPORTED ---
Severity:	minor	CC:	halla, lynx.mw+kde
Priority:	NOR
Version First Reported In:	5.1.5
Target Milestone:	---
Platform:	Ubuntu
OS:	Linux
Latest Commit:		Version Fixed/Implemented In:
Sentry Crash Report:

Description Isabelle 2023-03-01 12:40:47 UTC

The preset dimension for a5 300dpi is eh, kind of incorrect but maybe not, it's a bit confusing. 
Currently the dimensions are 1754 x 2480, but according to a bunch of website and the ISO standard (with a few calculations) it should be 1748 x 2480. The width is off by just a few pixels.

The width should be 1748 according to:
https://www.papersizes.org/a-sizes-in-pixels.htm
https://www.graphic-design-employment.com/a5-paper-dimensions.html
https://www.quill.com/content/index/paper-buying-guide/a5-paper-size-dimensions-usage/default.cshtml

It should be noted that adobe are rolling with the 1754:
https://www.adobe.com/uk/creativecloud/design/discover/a5-format.html

But I did some calculations myself:
According to the standard ISO_216 the size is rounded to millimeters. The dimension in mm for a5 is 148 x 210.
We only care about the width in this case, so let's keep working with only that: 148 mm
According to https://en.wikipedia.org/wiki/Inch the conversion number is 0.03937008
148 * 0.03937008 = 5.82677184 inches
Resolution is 300ppi
5.82677184 * 300 = 1748.031552 pixels
Rounding that gives 1748 pixels.

So 1748 x 2480 seems to be the ISO compliant dimensions for an a5 at 300ppi.

Comment 1 Halla Rempt 2023-03-01 15:24:05 UTC

But if we'd change it from 1743, we'd get all Adobe users after us with pitchforks...

Comment 2 Lynx3d 2023-03-11 23:05:53 UTC

I think the reason is very simple, A4 long edge is 3508 px (which is correctly rounded), and someone figured that A5 short edge (and A6 long edge) must obviously be 3508/2 = 1754. Who knows, it may even have slight practical advantages. A3 vs. A4 does not have that issue luckily, it rounds to exactly factor two.

As for being compliant, ISO also specifies a tolerance of +/- 1.5mm for lengths <= 150mm, so you can argue the "wrong" 1754 px (148.5...mm) is still easily within specs.