## Is Octave slow?

January 7, 2010

Some interesting tips from this blog

Advertisements

## MATLAB functions for computing relative luminance in W3C standard

August 11, 2009

I have written two MATLAB functions for computing relative luminance and contrast ratio using the Web Content Accessibility Guidelines (WCAG) 2.0.

Relative Luminance is the relative brightness of any point in a colorspace, normalized to 0 for darkest black and 1 for lightest white. For the sRGB colorspace, the relative luminance of a color is defined as

L = 0.2126 * R + 0.7152 * G + 0.0722 * B

where R, G and B are defined as:

if RsRGB <= 0.03928 then R = RsRGB/12.92 else R = ((RsRGB+0.055)/1.055) ^ 2.4

if GsRGB <= 0.03928 then G = GsRGB/12.92 else G = ((GsRGB+0.055)/1.055) ^ 2.4

if BsRGB <= 0.03928 then B = BsRGB/12.92 else B = ((BsRGB+0.055)/1.055) ^ 2.4

RsRGB, GsRGB, and BsRGB are defined as:

RsRGB = R8bit/255

GsRGB = G8bit/255

BsRGB = B8bit/255

while Contrast Ratio= (L1 + 0.05) / (L2 + 0.05), where

L1 is the relative luminance of the lighter of the colors, and

L2 is the relative luminance of the darker of the colors.

Contrast ratios can range from 1 to 21 (commonly written 1:1 to 21:1). the input is the rgb value (from 0 to 255) of the ligheter and the darker colors.

The WCAG guidelines indicate that contrast ratio should be at least 4.5:1

I have submitted the functions to matlab central. I think you will find there in few days. But I attach here the script

You can find the files at Matlab Central here.

———————————————————————————————————————

function relativeluminance = relativeluminance(erre,gi,bi)

% By Alessandro Farini 11 August 2009

%compute RsRGB as a value between 0 and 1

rsErre=erre/255;

rsGi=gi/255;

rsBi=bi/255;

%compute the value of RGB in sRGB space

if (rsErre>0.03928)

erreFinal=((rsErre+0.055)/1.055)^2.4;

else

erreFinal=rsErre/12.92;

end

if (rsGi>0.03928)

giFinal=((rsGi+0.055)/1.055)^2.4;

else

giFinal=rsGi/12.92;

end

if (rsBi>0.03928)

biFinal=((rsBi+0.055)/1.055)^2.4;

else

biFinal=rsBi/12.92;

end

%compute the relative luminance

relativeluminance = 0.2126*erreFinal + 0.7152*giFinal + 0.0722*biFinal;

——————————————————————————————————————–

function contrastratiow3c = contrastratiow3c(erreMax,giMax,biMax,erreMin,giMin,biMin)

% By Alessandro Farini 11 August 2009

%computing the relative luminance for the lighter and darker colors

elle1=relativeluminance(erreMax,giMax,biMax);

elle2=relativeluminance(erreMin,giMin,biMin);

contrastratiow3c=(elle1+0.05)/(elle2+0.05);

## A Technical blog….

August 10, 2009

Probably the contents of this blog will be quite technical. My non-technical blog is http://www.riflessioniottiche.it. I will use English language (in a terrible way) because in Italy there are very few people interested to this topic. Tommor I hope I will stsrt with the first post devoted to octave and matlab

## Hello world!

August 10, 2009

Welcome to WordPress.com. This is your first post. Edit or delete it and start blogging!