The 'A' in RGBA: What does it mean?

Kenny_Strawn · 03-08-2010, 08:48 PM

I know about Red, Green, and Blue, but I'm not so sure about the 'A'. What does it really mean?

I want to know this for this code:

Code:

int rgba (int Red, int Green, int Blue, int <WhateverTheAStandsFor>)
{
    return;
};

Essentially, I want to be able to use this code to fine-tune RGBA to my preferences, not just with "true" and "false", but with in-between options, so that I can control how transparent or opaque the desktop is going to be.

And I will do this with C++, not original C, unlike the existing Gtk RGBA module.

Sergei Steshenko · 03-08-2010, 08:51 PM

Quote:

Originally Posted by Kenny_Strawn

I know about Red, Green, and Blue, but I'm not so sure about the 'A'. What does it really mean?

I want to know this for this code:

Code:

int rgba (int Red, int Green, int Blue, int <WhateverTheAStandsFor>)
{
    return;
};

Essentially, I want to be able to use this code to fine-tune RGBA to my preferences, not just with "true" and "false", but with in-between options, so that I can control how transparent or opaque the desktop is going to be.

And I will do this with C++, not original C, unlike the existing Gtk RGBA module.

http://en.wikipedia.org/wiki/RGBA_color_space - are all your WEB search engines blocked ?

sundialsvcs · 03-09-2010, 10:26 PM

Briefly... the fourth channel ("A") is Alpha, which represents transparency.

A pixel with A=1.0 is "solid." A=0.0 is invisible. A=0.5 is a translucent "ghost."

This channel of information is used when blending multiple "layers" of material into a single image.

John VV · 03-09-2010, 10:53 PM

please use Google before posting

Alpha Chanel, for transparency

H_TeXMeX_H · 03-10-2010, 10:40 AM

Yeah, and that's why there is no real 32-bit color, it's 24-bit color + 8-bit alpha channel.

sundialsvcs · 03-10-2010, 10:43 PM

That depends upon your particular display hardware.

Remember... "RGB(A)" is simply a color space, just like CMYK and HSV(A). It is an agreed-upon method of representing color. The integer (or, as the case may be, floating-point) domain of each value can vary from file to file, application to application, or device to device.

The essence of "RGBA" is that "a color value is expressed by a 4-tuple {r,g,b,a}." That's it. That's all.