WebAIM - Web Accessibility In Mind

E-mail List Archives

Re: Color Contrast

for

From: Sven Jenzer
Date: Jun 4, 2009 3:45AM

i know these discussions with designers and let me add some arguments to
localise the problem:

1. Photoshop is allways showing the original size of a picture. This
size is relativ! If you have a print-quality image with 300 Pixel / Inch
and you put 14pt Text on it, this text will have an other output-size
than 14pt Text on the same picture scaled down to Screensize 72 Pixel /
Inch. The output-size depends on the definitions of the filesize and is
absolute. But the view of the file in Photoshop is not.
A Designer uses in Photoshop to display a picture in 100% - what does
this 100% mean? It means that 1 Original Pixel of the Image is one real
Pixel of the Screen you are using. Measuring this size or comparing it
with real measures is dangerous, it needs a scaling to a defined
output-size first. Beware of comparing Font-Measures with Photoshop.

2. If your AD need exact work: Use a DTP-Program like Quark, Indesign or
Illustrator (in Print-Modus !) to compare the Font-Sizes in DTP-Points.
You could print-out Arial in 14 pt and 18 pt and stick it on the frame
of the screen.

3. The font-size comparison given by Jared is supposably the simple
truth for WCAG. The hole world is relative (as we know since Albert
Einstein ;-)

best regards
Sven Jenzer


David Ashleydale schrieb:
> Hi,
>
> Sorry to keep harping on this, but could someone help me find a definitive
> answer to the points vs. pixels thing? My designers keep telling me that
> Photoshop, Illustrator, etc. are their main tools and that when the WCAG
> standard says "14 pt / bold" can be considered "large", they think they
> should be able to choose 14 pt and bold in Photoshop and have that work. I
> took a look at what Photoshop considers to be 14 pt and it's a lot smaller
> than what HTML considers to be 14 pt.
>
> But they insist that they are following the WCAG standard because they chose
> 14 pt in Photoshop.
>
> Do any of you have an explanation for this that I can give to them? Is there
> a reason that 14 pt in Photoshop would be different than 14 pt in HTML?
> Which one did the WCAG mean? When I look at WebAIM's Color Contrast Checker,
> there is a sentence that says "I am big text." I looked at the source and it
> says that it is 14 pt and bold. This 14 pt is much larger than the 14 pt
> that Photoshop uses by default.
>
> 1.2 em and 1.5 em are useful units, but how big is 1 em? If it's 16 px, then
> 1.2 em would be about 19 px and 1.5 em would be 24 px. But one of our
> designers said he thought that 1 em was equal to 12 px, not 16 px.
>
> If choosing 14 pt in Photoshop is incorrect for following this standard,
> what should the procedure be for using Photoshop?
>
> Any help on this would be greatly appreciated. It's causing quite a stir in
> my company. ;-)
>
> Thanks,
> David
>