= Deep raster effects =

You can use the extra information in deep raster images, such as Depth,
Normals, and various mattes, in more advanced compositing operations.
See [rendering deep raster images|] .

== Merge deep raster information in separate files ==

    The renderer can store the extra information in a single deep-raster
    file format (`.pic`), or in multiple "shallow" files. You may need
    to merge color planes together with the deep raster information, for
    certain operations (like [Z Composite|Node:cop2/zcomp], which
    requires `Zdepth` to be present in the input).

    For deep rasters that have been saved over several files, you will
    need to merge the deep raster planes and the color planes into a
    single sequence. See  [how to import an image as a plane of another
    image|planes] .

== Adjust render passes ==

    * In your surface shaders, you can export float (or vector3)
      variables such as diffuse, specular and ambient. You must write
      the appropriate values to them; they are not automatically filled
      in.

    * With scalar (matte) information, you can use the mattes as masks
      for color correction operations, or other filters like blur, to
      adjust portions of the image.

    * With vector3 (color) information, you can subtract the pass color
      from the image color (C), manipulate it, and then add it back into
      the composite. You can also use vector3 mattes as masks, just as
      scalars, but the mask will be applied as a 3 channel mask (Mask.R,
      Mask.G, Mask.B) and affect the different color channels
      differently.

    * You can do similar operations on shadow passes, allowing you to
      darken, blur or add noise to shadows.

== Z-depth compositing ==

    Z depth compositing is useful for compositing volumes or particles.
    For example, compositing falling snow around foreground elements.

    steps>>
        # To do Z depth compositing, each COP needs either a depth
          (`Pz`) or point (`P`) plane.

        # Use the [Z Composite operator|Node:cop2/zcomp] to composite
          the images, instead of a traditional " [over|layers] ".
          In addition to transparency, Z Composite looks at the Z depth
          of each point to see if it should be in front of or behind the
          other image.

    NOTE:
        The depth information is also updated with the new Z positions,
        so you can do multiple Z composites in series correctly.


    TIP:
        If you have many Z composites to perform and some have
        transparency, put all the Z composites dealing with transparent
        images at the end of the Z composite chain, if possible. This
        will minimize problems with Z compositing and transparency
        (since only 1 Z value can be stored, and transparency requires
        one for each transparent surface, plus the final opaque
        surface).

== Relighting ==

    _Relighting_ involves simulating the effect of adding extra lights
    to the rendered image. Houdini uses the depth and angle information
    encoded in the deep raster to calculate the interaction of the new
    lights with the surfaces in the image.

    steps>>
        # To do 3D lighting, you must have Point and Normal planes in
          your image.

        # Use the [Lighting operator|Node:cop2/light] to position a
          single directional or non-directional light in the scene, or
          do volume lighting with the parameters on the Lighting node's
          __Atmospheric__ tab.


    TIP:
        You can generate a normal map from a point map with the
        [Lighting operator|Node:cop2/light], but the results are not as
        smooth as when you render out a real Normal plane.


    NOTE:
        To add multiple lights, input the image to multiple Lighting
        nodes and turn off the __Add to original color__ parameter in
        each. Then  [use an Add or Screen operation|/composite/layers]  to
        combine the output of the nodes.


== Depth of field ==

    You can use the depth information encoded in the deep raster to
    adjust the apparent depth of field in the image, but de-focusing
    parts of the image outside the focus range.

    steps>>
        # To adjust the depth of field, the image must have a Z-depth or
          Point plane.

        # Create a [Depth of Field node|Node:cop2/dof] and a
          [Defocus|Node:cop2/defocus] (recommended) or
          [Blur|Node:cop2/blur] node.

          The Depth of Field operator works by generating a mask plane
          (`M`) from the depth information in the image, which you then
          use as a  [mask|/composite/masks]  for the [Defocus|Node:cop2/defocus] node.

        # Connect the image into the Depth of Field node and the
          [Defocus|Node:cop2/defocus] node. Connect the image into the
          [Defocus|Node:cop2/defocus] node as well. Finally, connect the Depth of
          Field node into the  [mask input|/composite/masks]  of the
          [Defocus|Node:cop2/defocus] node.

          [Image:images/dof.jpg]

        # Append a [Defocus COP|Node:cop2/defocus]; set the __Per Pixel Defocus__ parameter. Adjust the size to get the desired amount of blur.

          [Image:images/depth_of_field_image.jpg]


    TIP:
        See  [how to preview different planes|/nodes/cop2]  in the node
        tile's thumbnail.

== Fog ==

    Use the [Fog operator|Node:cop2/fog] to add various atmospheric
    effects to your network, such as normal fog, layered fog, and heat
    waves. The image must have a Z-depth plane or Point plane.

    * For normal fog, you can specify the color of the fog and its
      density.

    * For layered fog, you can specify the above plus the height that it
      starts/ends at, plus a drop-off region to make the transition
      smooth.

    * You can add 3D noise to the fog to make it more varied (though
      this takes quite a bit longer, as it does ray marching through the
      noise).

    * You can add an image to the Fog node's second input, which varies
      the fog color based on the second image's color.

    [Image:images/normal_fog.jpg]

    [Image:images/noisy_layer_fog.jpg]

== Apply an environment map ==

    Use the [Environment operator|Node:cop2/env] to apply an [environment
    map|/light/map] to an image. The image must have a Point plane and a Normal
    plane.

    The Environment operator supports Spherical, Cube-Strip and
    Cube-Cross maps. You can rotate map around the image, and blend it
    with the original image colors

== World space pixel culling ==

    Use the [Geo Key operator|Node:cop2/geokey] to partition, or cut
    out, areas of the image based upon their 3D position or normal
    direction.

    For images with a Point plane, use clipping planes and distance from
    a point to isolate or remove elements.

    Use a static direction vector to isolate all normals pointing in
    that direction. Use a point to isolate all normals pointing towards
    that point.

    To get a smooth transition, you can use a drop-off area or angle.

    Point:
        All points removed close to a given point.

        [Image:images/geo_clip_point.jpg]

    Angle:
        All points kept facing a certain direction (up).

        [Image:images/geo_clip_angle.jpg]

    Plane:
        All points removed in front of a plane.

        [Image:images/geo_clip_plane.jpg]