# dynamic range

Hi,

I am not sure if I am allowed to ask something out of Radiance commands but I venture this because I don't know any other forum where can someone answer this.

I am studying High Dynamic Range Image Encodings (G. Ward) and in order to undrestand some things better I would like to ask the following:
a) does dynamic range 1000:1 same as 1 order of magnitude?
b) what is maximum dynamic range that can exist in real world?
c) what dynamic range can human eye see?
d) what do we mean with cd/(m^2) ? where m^2: m=base, 2 = exponent

Thanks,
Despina

Despina,

a) does dynamic range 1000:1 same as 1 order of magnitude?

1 OoM is like shifting the decimal point to the left/right by one digit
(divide/multiply by 10), so 1000:1 = 3 OoM

b) what is maximum dynamic range that can exist in real world?

Very much depends on your scene: The sun has a luminance of 10^9 cd/m2,
and 'no light at all' would be 0 cd/m2.

c) what dynamic range can human eye see?

http://luminance.londonmet.ac.uk/webhdr/

d) what do we mean with cd/(m^2) ? where m^2: m=base, 2 = exponent

candela per meter square is the unit of luminance. 2 is not an exponent,
just a simple square.
http://www.learn.londonmet.ac.uk/packages/synthlight/handbook/index.html

Axel

Thanks Axel,
your ansewer was very explanotory and the webHDR webpage as well.

I have another question on this - how we compute Dynamic Range?
If for example: the brightest pixel has luminance 50 000 cd/m^2 and the darkest one 5 cd/m^2
is dynamic range 50 000/5 = 10 000:1? is that correct?
(i.e. 4 OoM)

And something more... is there any standard threshold, that "seperates" dynamic range to High and Low?

Thanks again,
Despina

···

----- Original Message ----- From: "Axel Jacobs" <a.jacobs@londonmet.ac.uk>
Sent: Tuesday, March 29, 2005 5:57 PM

Despina,

a) does dynamic range 1000:1 same as 1 order of magnitude?

1 OoM is like shifting the decimal point to the left/right by one digit
(divide/multiply by 10), so 1000:1 = 3 OoM

b) what is maximum dynamic range that can exist in real world?

Very much depends on your scene: The sun has a luminance of 10^9 cd/m2,
and 'no light at all' would be 0 cd/m2.

c) what dynamic range can human eye see?

http://luminance.londonmet.ac.uk/webhdr/

d) what do we mean with cd/(m^2) ? where m^2: m=base, 2 = exponent

candela per meter square is the unit of luminance. 2 is not an exponent,
just a simple square.
http://www.learn.londonmet.ac.uk/packages/synthlight/handbook/index.html

Axel

_______________________________________________

I have another question on this - how we compute Dynamic Range?
If for example: the brightest pixel has luminance 50 000 cd/m^2 and the
darkest one 5 cd/m^2
is dynamic range 50 000/5 = 10 000:1? is that correct?
(i.e. 4 OoM)

That looks right. It's easier in exponential notation -- the division
becomes a subtraction then: 5*10^5 / 5*10^1 = (5/5) * 10^(5-1) = 10 000

And something more... is there any standard threshold, that "seperates"
dynamic range to High and Low?

Not to my knowledge. However, it's save to assume that all images are low
DR, except for the ones that explicitly say that they are high. They must
then be stored in a file format that supports HDR, _and_ be created
suitably. It is possible to have a LDR image stored in a HDR file (e.g.
orders of magnitude (Just winding you up...)