MIL-HDBK-1300A
TABLE I. Application guidance for bandwidth compression algorithms. - Continued
Compression Algorithm |
Image Type |
Use |
ARIDPCM (IC field code C2) |
Grayscale/color eight-bits, 11-bits per pixel unblocked images |
When speed of compression or rate control of the compressed data is more important than image quality. The JPEG should be used for compression for all other instances of grayscale/color images. NITF 2.0 implementations are not required to compress images using ARIDPCM, but must be capable of interpreting them. |
JPEG DCT (IC field code C3 or M3) |
Grayscale/color eight-bits, 12-bits per pixel images |
This is the default for compressing grayscale/color images. This provides greater compression than ARIDPCM for similar image quality. |
Vector Quantization (IC field code C4 or M4) |
Gray scale/color, any pixel depth |
Very fast decompression, slow compression Good for static images (i.e. map backgrounds, etc.) Good image quality at moderate compression ratios (4:1 to 8:1) Can easily be combined with color quantization to increase compression ratios (12:1 to 24:1) |
5.5.1.1 Bi-level compression. The bi-level compression algorithm is used for encoding bi- level image and overlay information. This algorithm is consistent with the one- and two-dimension coding algorithms specified by Recommendation T.4 of the International Telegraph and Telephone Consultative Committee (CCITT) and MIL-STD-188-161 for group 3 facsimile devices. Uncoded or uncompressed data are represented by on bpp. This encoded data are composed of alternating run lengths of pixels of identical color with a maximum of 2560 pixels in one horizontal scan line or binary overlay information. Compression is achieved by encoding the run lengths with a series of specified Huffman codes. The one-dimensional algorithm codes individual scan lines. The two-dimensional algorithm is an extension of the one-dimensional method where vertical correlation between pixels is encoded in addition to the horizontal correlation. These algorithms are a lossless coding of bi-level information that can be decoded without incurring any degradation in the data. More detail on this specific algorithm can be found in MIL-STD-188-196.
5.5.1.2 ARIDPCM. The ARIDPCM is a compression algorithm that compresses 8- and 11-bit gray scale image data. This algorithm met the needs of the NITF in 1984 for low complexity or high speed compression on a PC-AT class personal computer. ARIDPCM is a spatial compression algorithm that uses simple linear and bilinear interpolation to predict image pixel values that are subtracted from the original values to produce delta values in a local 8 x 8 neighborhood. These delta values are quantized using a static look-up table. Figures 6 and 7 show the procedure for the ARIDPCM compression and decompression. Three modes of the ARIDPCM: are nondriven, driven, and composite. The nondriven mode is chosen when a specific quality is desired, but the length of the coded image is variable. To guarantee a specific average number of bpp over the entire image, the driven mode is chosen. The driven mode is defined with four selectable compression rates (4.5, 2.3,
1.4, and 0.75 bpp) for 8-bit data and four compression rates (6.4, 4.5, 2.3, and 1.4 bpp) for 11-
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