# Pictures

RenderWorld has the ability to import rgb images and represent them as "billboards" which may be placed any where in the scene at any orientation, and move about as any other object does. The pictures act as a light emitting flat rectangular surface. In the near-future, the alpha channel of rgba files will be used as a pixel-fraction-unfilled in order to see behind transparent portions of the billboard. Because rgb images are represented in terms of integers and not in terms of physical light levels, the picture object includes parameters for converting the integers to physical light levels.

The form for creating the picture object in the scene file is the same as with all other objects:

           number_of_times 1
           time x   y  z   theta phi  chi
           0    500 0  30  90    180 180
           name: pictureabc
           type: picture
           input: picture_boat.dat
           priority: 3

The x, y, z position of the picture refers to the center of the rectangle the picture lies on. The orientation is with respect to that center. Note that theta=0 means that the picture lies flat, and theta=90 is for a picture oriented straight up facing horizontal. The file `picture_boat.dat` has the form:

           RenderWorld_data_file picture 2 2
           number_of_bands 3
           band_id 1 2 3
           dimensions 300 100
           picture_file boat.rgb
           frontside picture
           min_radiance 0 0 0
           max_radiance 20. 20. 20.
           backside solid
           color 500 100 50
           reflectivity 0 0 0
           transmission 1 1 1
           image_method 0
           end

The `dimensions` of the picture are the physical length and width in units of meters. The file containing the 24-bit sgi rgb format image is listed in the `picture_file` line. The image can be placed on the `frontside` of the picture as shown. If you do not want the image on the frontside, use

           frontside solid
           color 500 100 50
           reflectivity 0 0 0
           transmission 1 1 1

where `color` is the intensity values in each of the channels. Independently the image can also be placed on the backside or not using `backside` `picture` or `backside` `solid`. For `backside` `picture` the `color`, `reflectivity`, and `transmission` lines must be replaced with `min_radiance` and `max_radiance` lines.

The 8 bit/channel digital range of the sgi rgb images is mapped linearly into a minimum and maximum light level separately for each channel in the two lines

           min_radiance 0 0 0
           max_radiance 20. 20. 20.

The lines for `reflectivity` and `transmission` are not currently used. The choice `image_method` `0` puts the billboard picture in the full scene, including its primary image and any reflection/refraction/transmission from other environmental components. The choice `image_method` `1` removes the primary image of the picture object, while retaining any reflection/refraction/transmission.

### Pictures with Alpha Channel Textures and Animation

Pictures can use an alpha channel in the same way as the skydome. The format for the picture input file is:

           RenderWorld_data_file picture 3 3
           number_of_bands 3
           band_id 1 2 3
           dimensions 300 100
           picture_file boat.rgb
           animate frames
           use_alpha 1
           frontside picture
           min_radiance 0 0 0
           max_radiance 20. 20. 20.
           backside solid
           color 500 100 50
           reflectivity 0 0 0
           transmission 1 1 1
           image_method 0
           end

The line beginning with `animate` determines whether the picture images are animated. The options are `no` and `frames`. When `frames` is chosen, RenderWorld tries to read the file `boat.rgb.xxxx` for frame xxxx (with leading zeroes).

The alpha channel of the picture is used when `use_alpha` has the value `1` or `2` (0 is the no alpha choice). For the value `1`, the background is attenuated by the alpha, and for the choice of `2`, the background is attenuated and the picture texture is conditioned by the alpha.

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