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#Actualskytiger

Posted 31 March 2013 - 08:05 AM

Yes

 

I agree with what you say

 

But I think that few people realise that:

 

"gamma correction" on a digital camera

is actually lightness (aka brightness) correction

it has NOTHING to do with monitor gamma

and is used to ensure sufficient precision for the dark shades in an 8 bpp image (to avoid banding)

 

whereas:

 

gamma correction on a gpu

is really gamma correction

it has NOTHING to do with human perception

and is used to solve the problem of non-linear monitor response

 

the fact that you can use the same gamma for 2 completely different purposes is purely COINCIDENCE

 

and has a useful side-effect that direct display of the gamma corrected image on a monitor looks OK

 

 

PS

 

"Luminance" is not a physical value, it is a Photometric value

"Radiance" is a physical value

 

They are almost identical within the visible spectrum of light

so for our purposes they are the same ...

 

But Luminance is adjusted for the non-linear response of human eye based on wavelength

 

Renderers work with Radiance - the mapping from Radiance to Luminance happens inside the human eye

 

Outside of the visible spectrum Luminance is always ZERO

 

luminance = radiance * is_visible(wavelength) ? 1 : 0;


#2skytiger

Posted 31 March 2013 - 08:03 AM

Yes

 

I agree with what you say

 

But I think that few people realise that:

 

"gamma correction" on a digital camera

is actually lightness (aka brightness) correction

it has NOTHING to do with monitor gamma

and is used to ensure sufficient precision for the dark shades in an 8 bpp image

 

whereas:

 

gamma correction on a gpu

is really gamma correction

it has NOTHING to do with human perception

and is used to solve the problem of non-linear monitor response

 

the fact that you can use the same gamma for 2 completely different purposes is purely COINCIDENCE

 

and has a useful side-effect that direct display of the gamma corrected image on a monitor looks OK

 

 

PS

 

"Luminance" is not a physical value, it is a Photometric value

"Radiance" is a physical value

 

They are almost identical within the visible spectrum of light

so for our purposes they are the same ...

 

But Luminance is adjusted for the non-linear response of human eye based on wavelength

 

Renderers work with Radiance - the mapping from Radiance to Luminance happens inside the human eye

 

Outside of the visible spectrum Luminance is always ZERO

 

luminance = radiance * is_visible(wavelength) ? 1 : 0;


#1skytiger

Posted 31 March 2013 - 05:43 AM

Yes

 

I agree with what you say

 

But I think that few people realise that:

 

"gamma correction" on a digital camera

is actually lightness (aka brightness) correction

it has NOTHING to do with monitor gamma

and is used to ensure sufficient precision for the dark shades in an 8 bpp image

 

whereas:

 

gamma correction on a gpu

is really gamma correction

it has NOTHING to do with human perception

and is used to solve the problem of non-linear monitor response

 

the fact that you can use the same gamma for 2 completely different purposes is purely COINCIDENCE

 

and has a useful side-effect that direct display of the gamma corrected image on a monitor looks OK

 

 

PS

 

"Luminance" is not a physical value, it is a Photometric value

"Radiance" is a physical value

 

They are almost identical within the visible spectrum of light

so for our purposes they are the same ...

 

But Luminance is adjusted for the non-linear response of human eye based on color

 

Renderers work with Radiance - the mapping from Radiance to Luminance happens inside the human eye

 

Outside of the visible spectrum Luminance is always ZERO

 

luminance = radiance * is_visible(wavelength) ? 1 : 0;


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