MIL-HDBK-1300A
elements that may duplicate communication protocol standards (for example, originator, classification, date-time-group). A diagram of the NITF file structure is shown on figure 5.
FIGURE 5. NITF file structure.
5.3 Data types. The NITF explicitly supports inclusion of four types or kinds of data: images, symbols, labels, and text. In addition, the NITF accommodates future needs and user-specific needs by providing a structured way to incorporate new kinds of data.
5.3.1 Images. The image data type is used in the NITF to store the image data, which encompasses multispectral imagery and images intended to be displayed as monochrome (shades of gray), color-mapped, or true color. That is, an image may include multiple data bands and color LUT, the latter within the image's header fields. True color images (three band) may be specified to be interpreted using either the RGB (Red, Green, Blue) or the YCbCr601 (Y = Brightness of signal,
Cb = Chrominance (blue), Cr = Chrominance (red)) color system. Images may be represented with user-selectable (from a variety of choices) blocking and interleaving of the image pixel values.
5.3.1.1 Blocked images. In some instances, an NITF image may be represented by an orderly set of subimages (or subarrays) called blocks. Image blocks are of uniform size within a single
image, and are arranged in n rows and m columns to form a complete image. The blocks are recorded/transmitted sequentially, in row major order; that is, all of the blocks of the first row are recorded/transmitted, followed by all of the blocks for the second row, and so on. Image blocks must be complete, so pad (transparent) pixels are added to fill out the images to the nearest block
boundary.
5.3.1.2 Blocked image masking. In some instances, a blocked image may have a considerable number of empty blocks. This might occur when a rectangular image is not north aligned, but has been rotated to a north up orientation. In this case, it is sometimes useful to not record or transmit empty blocks. However, if empty blocks are not recorded/transmitted, the image loses its logical structure as an image with n x m blocks. In order to preclude the loss of logical structure, and to allow the exclusion of empty blocks, a mask structure has been defined. The mask identifies the location of non-empty blocks, and tags empty blocks so that the using application can
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