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womble
Posts: 5494
Joined: 3/14/2005
From: Living on the edge
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Colour contrast analyser - 3/19/2007 19:07:19
quote:
...a tool for checking foreground & background colour combinations to determine if they provide good colour visibility. Determining "colour visibility" is based on algorithms suggested by the World Wide Web Consortium (W3C)
quote:
The Colour Contrast Analyser (CCA) is useful to help determine, in particular, the legibility of text on a web page and the legibility of image based representations of text.
Assessing conformance with Checkpoint 2.2 of the Web Content Accessibility Guidelines 1.0
Checkpoint 2.2 of the WCAG 1.0 requires that "foreground and background colour combinations provide sufficient contrast when viewed by someone having colour deficits, or when viewed on a black and white screen."
Use the CCA to test colour combinations against the W3C's suggested algorithm for determining "sufficient contrast".
http://www.nils.org.au/info.aspx?page=628
A nice little app. Enter either the hex number of the background and foreground colours, or use the dropper tool to select the colours, and get a result for both normal vision and different types of colour blindness, as well as seeing a simulation of an area of the screen for different types of colour blindness, and also see what you page might look like to someone with cataracts.
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~~ "A cruel god ain't no god at all" ~~
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mtfm
Posts: 421
Joined: 1/13/2006
From: Mesa, AZ
Status: offline
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RE: Colour contrast analyser - 3/20/2007 15:40:29
Looks cool, from what I can see. Might see if I can find someone round here who will let me try it on their computer.
Kind of ironic, though because this particular item is not available on Mac and therefore not accessible to yours truly.
(I have a Mac at home, and here at work I know better than to even ask about downloading freeware anything.)
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Is this possible? How about this? What about....?
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d a v e
Posts: 4041
Joined: 7/24/2002
From: England (but live in Finland now)
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RE: Colour contrast analyser - 3/20/2007 16:11:24
does the firefox extensions work for mac??
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David Prescott
Gekko web design
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rubyaim
Posts: 757
Joined: 6/22/2005
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RE: Colour contrast analyser - 3/20/2007 20:57:41
Out of idle curiosity I just did a search for luminosity and am really none the wiser.
http://www.w3.org/TR/WCAG20/appendixA.html
quote:
luminosity contrast ratio
(L1 + 0.05) / (L2 + 0.05), where L1 is the luminosity of the lighter of the text or background colors, and L2 is the luminosity of the darker of the text or background colors.
Note 1: The luminosity of a color is defined as 0.2126 * ((R / FS) ^ 2.2) + 0.7152 * ((G / FS) ^ 2.2) + 0.0722 * ((B / FS) ^ 2.2).
*
R, G, and B are the red, green, and blue RGB values of the color.
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FS is the maximum possible full scale RGB value for R, G, and B (255 for eight bit color channels).
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The "^" character is the exponentiation operator.
Note 2: Luminosity values can range from 0 (black) to 1 (white), and luminosity contrast ratios can range from 1 to 21.
The thing at Jucy Studio about Luminosity Contrast Ratio Algorithm was a bit better.
I think I'll just continue to rely on common sense 
Jaybee, maybe #fff and #f00 share too many f's when divided by #ddd, multiplied by 1258.3333345, and then subtracted from 2 
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Sally
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womble
Posts: 5494
Joined: 3/14/2005
From: Living on the edge
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RE: Colour contrast analyser - 3/21/2007 10:41:29
quote:
ORIGINAL: Donkey
If your site passes on the various criteria for colourblind people (simply put if it's legible when viewed in grayscale) that's all that matters. Any non-colourblind person who may have a problem distinguishing between background and foreground colours that look OK in grayscale should be using a screenreader.
This colour facisim is wrong headed and should be rethought before it becomes accepted wisdom and nobody dares to challenge it.
quote:
Any non-colourblind person who may have a problem distinguishing between background and foreground colours that look OK in grayscale should be using a screenreader.
Not true.
As some of you know, I have some visual problems due to a neurological condition, problems which have recently been getting worse, and thus spent this morning online window shopping for screen magnification software, and I discovered the number of sites selling assistive technologies who have serious accessibility problems in some areas is rather alarmingly high. That's a different story though.
Apart from having very variable visual accuity, I also have double vision, which isn't fully corrected by all the prisms my specs are loaded up with. Result? Sometimes, not bad, other times fuzzy and quite a few echoes of the same image overlapping. Even something that's fairly okay in greyscale, when made fuzzy and multiplied, loses it's clarity, so the contrast has to be very strong. Depending on which computer I'm on I can vary the resolution - at work I have particular problems so that's on 800x600 on a 21" monitor at the moment. On a bad day if I'm in the office I'll do stuff that doesn't need the computer, and if it's a 'web' day, the computer unfortunately stays off.
I certainly don't think I'm quite ready for a screenreader just yet though.
Luminosity's also important for a variety of reasons, including incidently sometimes for people with normal vision. I run a forum for people with the same condition I have, and when we recently moved sites and I installed different forum software there were howls of protest at the colour scheme and even one of my admins walked out and refused to come back until I installed a different theme. Why? There was plenty of contrast - because the background was white - #fff. That was a problem because a lot of the forum members suffer from photophobia - a sensitivity to light. Bright white backgrounds have too much 'glare'. Other conditions produce different problems - a friend of mine has Usher Syndrome. As well as having tunnel vision, she has photophobia, and Retinitis pigmentosa so she also has problems with particular colour schemes because she finds it difficult to identify colours (not the same as colour-blindness). A screen reader wouldn't be much use to her because she's also profoundly deaf.
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~~ "A cruel god ain't no god at all" ~~
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