"Luminance" image data?

[Sage_Rat]

I’m working with a library for loading images called DevIL. Image formats that it supports are RGB, BGR, RGBA, BGRA, color index, and luminance. What’s a “luminance” data format? Is it just a fancy word for grayscale?

[griffin1977]

@Sage_Rat

I’m working with a library for loading images called DevIL. Image formats that it supports are RGB, BGR, RGBA, BGRA, color index, and luminance. What’s a “luminance” data format? Is it just a fancy word for grayscale?

Pretty much, yeah. Its a bit more complicated than that (strictly speaking luminance represents the brightness of an image taking into account how bright the different color channels appear to the human eye), but for all intents and purposes a luminance format is graysacale.

[Ximenean]

Perhaps they mean a system such as YCbCr. The article YUV probably explains the motivation behind it better.

[Sage_Rat]

Hm, well apparently they have the same value in OpenGL.

@OpenGL Documentation

GL_LUMINANCE
Each pixel is a single luminance component.
This component is converted to the internal floating-point format in
the same way the red component of an RGBA pixel is.
It is then converted to an RGBA pixel with red, green, and blue set to the
converted luminance value,
and alpha set to 1.
After this conversion, the pixel is treated as if it had been read
as an RGBA pixel.

Which seems to indicate that whatever it is, it does store color information, even if it’s in some wonky format.

[griffin1977]

@Sage_Rat

Hm, well apparently they have the same value in OpenGL.
Which seems to indicate that whatever it is, it does store color information, even if it’s in some wonky format.

No, only one component is stored in the luminance texture. After reading the value from the texture the resulting RGBA value will have identical RGB values set to whatever that value was (and an alpha value of 1.0).