TIFF Tag ImageLayer
|Code||34732 (hex 0x87AC)|
|Type||SHORT or LONG|
Defined in the Mixed Raster Content part of RFC 2301, used to denote the particular function of this Image in the mixed raster scheme.
Image layers are defined such that layer 1 is the Background layer, layer 3 is the Foreground layer, and layer 2 is the Mask layer, which selects pixels from the Background and Foreground layers. The ImageLayer tag contains two values, describing the layer to which the image belongs and the order in which it is imaged.
ImageLayer = 1, 2, 3.
1: Image is a Background image, i.e., the image that will appear whenever the Mask contains a value of 0. Background images typically contain low-resolution, continuous-tone imagery.
2: Image is the Mask layer. In MRC, if the Mask layer is present, it must be the Primary IFD and be full page in extent (no gaps.)
3: Image is a Foreground image, i.e., the image that will appear whenever the Mask contains a value of 1. The Foreground image generally defines the color of text or lines, but may also contain high-resolution imagery.
1: first image to be imaged in this layer,
2: second image to be imaged in this layer,
ImageLayer describes the image order. In MRC, this may be considered the strip number. Since MRC mode currently does not allow overlap between images within a layer, the order value does not have any visual effect.