3 replies to this topic

[sky_blue]

hi,

i want to estimate the albedo map of a face image. i need guidelines on how to do this.
P.S. the image doesn't have to be a human face--it can be anyother object. i just need the general technique.

[Reedbeta]

I'm not sure exactly what you mean by albedo map - I've only heard that term used to mean the same thing as the diffuse color map, which would just be the image itself. Can you clarify what you're looking for?

[sky_blue]

The ratio of the amount of light reflected by an object to the amount of incident light is termed as albedo.

I have a list of irradiance value and the corresponding light source direction.
from these information I have to compute surface normal. then I can determine the incident light as "incident light = light source direction dot surface normal".

so if u can tell me the formula for computing surface normal using light source direction, it will be of great help.

[Reedbeta]

So, you know what the albedo of a pixel is, and where the light is coming from, and you want to figure out the surface normal? Well, it depends on the surface's BRDF. If you assume a Lambertian BRDF, for instance, then reflected light is simply light-color * albedo * dot(normal, light-direction). The dot product is of course the cosine of the angle between those vectors, so you could take the arc-cosine. That would establish a cone of possible directions for the surface normal. You can't narrow it down any further than that by looking at one pixel at a time, though you might be able to do better by taking into account neighboring areas of the image, or if you have multiple light sources with linearly independent colors.