Reference:Image Pattern

Instead of placing the color of the image on the object like an image_map, an image_pattern specifies an entire texture item (color, pigment, normal or texture) based on the gray value at that point.

This gray-value is checked against a list and the corresponding item is then used for the texture at that particular point. For values between listed items, an averaged texture is calculated.

It takes a standard image specification and has one option, use_alpha, which works similar to use_color or use_index.

Note: See the section Using the Alpha Channel for some important information regarding the use of image_pattern.

Syntax:

PIGMENT:
  pigment {
    IMAGE_PATTERN
    color_map { COLOR_MAP_BODY } |
    colour_map { COLOR_MAP_BODY } | 
    pigment_map { PIGMENT_MAP_BODY }
    }

NORMAL:
  normal {
    IMAGE_PATTERN [Bump_Size]
    normal_map { NORMAL_MAP_BODY }
    }

TEXTURE:
  texture {
    IMAGE_PATTERN
    texture_map { TEXTURE_MAP_BODY }
    }

IMAGE_PATTERN:
  image_pattern {
    BITMAP_TYPE "bitmap.ext" [gamma GAMMA] [premultiplied BOOL]
    [IMAGE_MAP_MODS...]
    }

IMAGE_MAP_MOD:
  map_type Type | once | interpolate Type | use_alpha
  ITEM_MAP_BODY:
  ITEM_MAP_IDENTIFIER | ITEM_MAP_ENTRY...
  ITEM_MAP_ENTRY:
  [ GRAY_VALUE  ITEM_MAP_ENTRY... ]

It is also useful for creating texture masks, like the following:

texture {
  image_pattern { tga "image.tga" use_alpha }
  texture_map {
    [0 Mytex ]
    [1 pigment { transmit 1 } ]
    }
  }

Note: This pattern uses an image to get the gray values from. If you want exactly the same possibilities but need to get gray values from a pigment, you can use the pigment_pattern.

While POV-Ray will normally interpret the image pattern input file as a container of linear data irregardless of file type, this can be overridden for any individual image pattern input file by specifying gamma GAMMA immediately after the file name. For example:

image_pattern {
  jpeg "foobar.jpg" gamma 1.8
  }

This will cause POV-Ray to perform gamma adjustment or -decoding on the input file data before building the image pattern. Alternatively to a numerical value, srgb may be specified to denote that the file format is pre-corrected or encoded using the sRGB transfer function instead of a power-law gamma function. See section Gamma Handling for more information on gamma.