# Blender 3D: Noob to Pro/Baking

Blender can render radiosity, a method of calculating realistic lighting, in which light is emitted and transferred using a method similar to that by which heat is transferred.

## Tutorial, Introduction to Radiosity

No tutorial as of yet.

## Terms Used for Blender Radiosity

Element
    Light-receiving mesh, data to be lit. (Meshes with material's emit value set to zero will only be treated as elements.)
Patch
    Light-emitting faces of a mesh, where the material applied to that face has an emit value above zero.
Note Once lit, elements will be used as patches, so that light can bounce a number of times.
Patches can also be lit by other patches and therefore treated as elements.

## Lighting Geometry

In Blender detail in lighting is gained by subdividing the mesh, therefore baked meshes will usually have many more faces than the original.
Some facts about radiosity
* The centre of the face is used when emitting light.
* The area of the face will determine how much light it casts.
* Triangles often cause uneven subdivision, giving worse results and less even lighting. Use quads where possible.
* For best results when making a mesh for radiosity baking, long skinny faces will cause artifacts, triangles even more so.
* Radiosity is an iterative process that is continually refined until any of the user-set limits are reached (i.e. the smallest element or the maximum number of elements is reached.) You may stop radiosity calculation early by pressing escape at any time even though your limits are not reached.

## Radiosity Settings

Hemires
    This adjusts the resolution of the Hemicube,
    The hemicube is a 3D Grid than spans the bounding box of all objects to which you are applying radiosity.
    This grid is used for calculating the path of light emitted from one object to another.
    The resolution is the number of subdivisions along the X,Y and Z axis, not related to Blender units, affecting how fine grained the light calculations will be.
    A low value may result in noisy scattering of colour, whereas a higher value will be smooth in tone.
    Note that with smaller scenes that are less complex, a lower resolution may give good results much more quickly.
Max Iterations
    Limits the number of radiosity rounds, 0 is unlimited. If used, this value should be greater or equal to the total number of emitting faces. :Hint It is probably best to keep this value at 0 to make sure all light-emitting faces are evaluated.
Add New Meshes
    Adds new radiosity baked meshes into active current layers.
    Hint leave some empty layers to add the new mesh into, keeping the original meshes separate from the radiosity allied mesh.
Multi and Gamma
    Lighting adjustment, use after radiosity is baked.
Convergence
    Sets the threshold for light to keep bouncing. lower threshold will keep lower energy light bouncing.
    A high Convergence can prevent dim lights from being used at all.
    A higher value is faster.
Collect Meshes
    Collect selected meshes for radiosity computation.
PaMin
    This will effects 2 things,
    1) The minimum size of faces that will be used as a light-emitting patch, and
    2) the minimum size to which a light-emitting face will be subdivided.
PaMax
    This will effects 2 things,
    The maximum size of faces that will be used as a light-emitting patch, and the maximum size at which an element may be used as a light, when it is subsequently lit by another patch.
    This is important because large faces my be evaluated as a single patch and light surrounding faces from the faces centre point, causing uneven lighting.
SubSh Patch and Element
    Sub Shoot Patch/Element effects how many times the face is tested for subdivision. More tests mean that it will incrementally subdivide, calculating the patch/element that needs the most detail each time, rather then performing subdivisions fewer times, resulting in a more uniformly subdivided area.
    The subdivisions are limited by the ElMin and PaMin, and will stop if all faces reach this size limit.
    A Zero value will for either of these makes the number of possible tests unlimited.
SubSh Patch
    Subdividing shoot patches is a way of having patches that are originally large patches subdivided so that lighting casts from each new subdivided patch, resulting in softer shadows.
    The subdivisions are limited by PaMin, which sets how small patches may be before they stop subdividing.
SubSh Element
    Sub Shoot Patch effects how many times per shoot elements can be subdivided.
    Subdividing elements is the method used to add detail in what would otherwise be a flat area of colour.
MaxEl
    The total number of faces for the final result. This value is useful for limiting the quality and time taken for the final result. Use a lower value to start with. For meshes that are already highly subdivided you can even use 0 and have no subdivision.
    Also Note that sometimes a lower value will distribute polygons more effectively and give as good a result as a higher setting.

## Trouble Shooting

Q. The result looks bad: tone is uneven, as if added in the wrong areas.
A. Its likely your mesh has skinny faces. Try make your mesh with even faces, quads where possible.
Q. The tone on areas that should be smooth is uneven and blotchy.
A. Setting a higher Hemires will solve this problem.
Q. I'm getting light refracted white areas when one element reflects onto another.
A. Your PaMax setting is too high. Your element is reflecting light from the centre of an area that is too large. and will reflect light from a small number of large patches. Make the PaMax lower.