Indigo Renderer Forum

Why is the C value for the exponent slot set to 100 by default? I always set this back to 0... Should I not be doing this?

An exponent of zero is extremely rough. A default of 100 is a more realistic roughness for a black texel in an exponent map.

This sounds like Exporter related, isn't it?

The C value should be 0 by default!

Afaik it is something like a plain addition (or subtraction) to the exponent Value.

So if you have for example a B value of 128 with a exponent Map and a C value of 50.
Then your Exponent map will drive the exponent with pure black from 50 to pure white 178.

OnoSendai wrote:An exponent of zero is extremely rough. A default of 100 is a more realistic roughness for a black texel in an exponent map.

But we use the B value for the base Exponent value. Why bother with a C default different then 0, simply set the B default to 100!

Zom-B wrote:But we use the B value for the base Exponent value. Why bother with a C default different then 0, simply set the B default to 100!

My point exactly. It's not that B value I'm referring to but the C value... This isn't exporter related it's if you make a new material in Indigo when you click on the exponent slot to load an image the C value is always set to 100...

Zom-B wrote:

OnoSendai wrote:An exponent of zero is extremely rough. A default of 100 is a more realistic roughness for a black texel in an exponent map.

But we use the B value for the base Exponent value. Why bother with a C default different then 0, simply set the B default to 100!

huh - I always think of the C value as the base and the B as the multiplier. so if I have a plastic that should be shinier/more-polished in spots, the C is the roughest I would want my material to be at any point. I would pretty much never use a value of 0 for the exponent of any phong. but 100 is definitely higher than what I use for some materials...just depends on the case.

It is entirely within the realm of posibily that I have been using this incorrectly for years! That's why I thought I'd ask

bubs wrote:huh - I always think of the C value as the base and the B as the multiplier. so if I have a plastic that should be shinier/more-polished in spots, the C is the roughest I would want my material to be at any point. I would pretty much never use a value of 0 for the exponent of any phong.

just so I understand... If I have an exponent with a B of 1000 and a C of 100 are you saying that when I use a black & white image file the completely white areas will effectively have an exp value of 1000 and the completely black areas a value of 100?

bubs wrote:

bubs wrote:huh - I always think of the C value as the base and the B as the multiplier. so if I have a plastic that should be shinier/more-polished in spots, the C is the roughest I would want my material to be at any point. I would pretty much never use a value of 0 for the exponent of any phong.

just so I understand... If I have an exponent with a B of 1000 and a C of 100 are you saying that when I use a black & white image file the completely white areas will effectively have an exp value of 1000 and the completely black areas a value of 100?

that has been my understanding. though it probably depends on gamma setting of the texture somewhat too. but this could probably be confirmed using a nice solid black and white checker texture and comparing to normal phong exp values set in the B and C slots

edit:
yeah, just confirmed this, see attached. regular phong with exp 1 and 1000, respectively, and then using a 100% black, 100% white checker texture for exponent with C value 1 and B value 1000.

every day is a school day! I've really always ignored the A & C values because I wasn't sure what they did... (still have no clue about A )

Might want to revisit every material I've ever uploaded to the database!

bubs wrote:Might want to revisit every material I've ever uploaded to the database!

Why that, he controlled everything using the B value, only raising the lowest exponent to 1 by having C @ 1!

P.S.
Here some more talk about ABC: http://www.indigorenderer.com/forum/vie ... 37&t=11633

Well it's just that if I've managed to get a material that looked like it had a good exponent value it's probably been a lot of good luck! I feel I have a much better understanding now...
It was always the preview image in the Indigo GUI which put me off altering the C value... as soon as you put it to 100 by image was always blown out completely to white... Maybe it's just me, but I don't think this element is very well explained in the manual... Thinking of this more as a maximum and minimum value is very helpful

bubs wrote:

bubs wrote:huh - I always think of the C value as the base and the B as the multiplier. so if I have a plastic that should be shinier/more-polished in spots, the C is the roughest I would want my material to be at any point. I would pretty much never use a value of 0 for the exponent of any phong.

just so I understand... If I have an exponent with a B of 1000 and a C of 100 are you saying that when I use a black & white image file the completely white areas will effectively have an exp value of 1000 and the completely black areas a value of 100?

No, the black will be 100 and the white 1100.
In the example from FakeShamus it will be 1 and 1001

By the way, a trick I give sometimes : you get more control over your exponent maps when setting a very high gamma to them, such as 4

Etienne