Re: [Gimp-developer] Don't make an architectural mistake based on a groundless premise

• From: Simone Karin Lehmann <simone lisanet de>
• To: "gimp-developer-list gnome org" <gimp-developer-list gnome org>
• Subject: Re: [Gimp-developer] Don't make an architectural mistake based on a groundless premise
• Date: Tue, 7 Oct 2014 01:57:23 +0200

```Hi,

although you and Elle are discussing this topic, I'd like to give my 2 cents

```
```Am 06.10.2014 um 21:54 schrieb Øyvind Kolås <pippin gimp org>:
To facilitate
cooperation between scientists, engineers and others we have developed
a convention of tagging numbers we use to refer to temperature with a
unit qualifier, like thus: 37.7°C 100°F 310.9°K. That way, given a set
of conversions formulas, it is possible to operate in the preferred
unit.
```
```
Of course, you can do operations in your preferred unit, but that does not mean, that your computation will
give identical results after you convert your result of your preferred unit back to the original unit. And
that's what you implicitly say: operating in a "converted unit" and converting back will give identical
results, as if operating in any original unit only. Or in GEGL/BABL words: operating in unbounded sRGB and
converting back to the original space will give identical results as operating in the original space only.

You've given a very good example for that:

If
x C = y F
and
x C = z T, where T is your "TCS" , your "temperature connection space"
is true,

you know that

2*x C != 2*y F
and
x C + 10 C != y F + 10 C
and
x C + 10 C != y F + 10 F

is true too.

and so although
2*x C = 2*z T
there is
2*z T != 2*y F
and
z T + 10 T != y F + 10 F

So doing an operation in T, either multiply or adding, and converting back, won't be the same as computing in
the original unit in your example. Same applies to color space computations and various operations.

BTW, I've noticed, that although Elle always gives equations or real world examples and images to prove her
statements, you don't. So, I'd like to ask you for such a mathematical equation or real world example for