JpegLL(3)
NAME
JPEG Lossless compressor/decompressor − JPEG Lossless compressor/decompressor for compressed image sequences
DESCRIPTION
The JPEG Lossless compresor/decompressor is the lossless variant of the Jpeg series of codecs (see Jpeg(3)). The lossless compression technique uses Differential Pulse Code Modulation (DPCM) with two-dimensional prediction and Huffman coding. It is the only codec in the current XIL compression suite which can operate on pixel data with greater than 8 bit precision. This compressor will accept input data of type XIL_BYTE or XIL_SHORT.
For more information and example programs, see the XIL Programmer’s Guide.
Creating a CIS
To compress a compressed image sequence (CIS) with the XIL JPEG Lossless compressor, specify "JpegLL" for the compressorname argument in xil_cis_create(3).
Getting and Setting Attributes
Use xil_cis_get_attribute(3) and xil_cis_set_attribute(3) to get and set JPEG Lossless CIS attributes. These attributes are described in the following sections. Refer to the example section for additional information.
JpegLL Compression Attributes
The following paragraphs describe the JPEG Lossless CIS attributes available with the XIL library. All structures and enumerations are defined via xil.h. Note that some attributes are "set-only" and others are "get-only." This is noted under the Access heading for each attribute.
Note that if you are setting an attribute and that attribute is a structure, you must pass the address of that structure. If you are getting an attribute, you must always pass its address.
COMPRESSED_DATA_FORMAT
Description defines output format for JPEG Lossless compressor
Access set
Type typedef enum{
INTERCHANGE, ABBREVIATED_FORMAT
} XilJpegCompressedDataFormat;
Values INTERCHANGE: Use JPEG interchange format. All quantization and entropy-coding table specifications needed by the decoding process are included in each compressed frame. ABBREVIATED_IMAGE: Use JPEG abbreviated format for compressed images. Quantization and entropy-coding table specifications are not included in a compressed frame if the specifications are defined in a previous frame in the compressed sequence. If any table values change after they are defined in the compressed sequence, a new table definition is included in the first compressed frame that uses the new table values.
Default ABBREVIATED_IMAGE
Notes This does not include the third type: ABBREVIATED_TABLE, in which a frame contains only table specifications. However, the decoder will accept this format.
ENCODE_INTERLEAVED
Description If the image to compress is composed of 4 bands or less, having this attribute set to TRUE will generate an interleaved JPEG-compliant bitstream. In this form, encoded pixels are interleaved by band. If the number of bands exceeds 4 or if this attribute is set to FALSE, a noninterleaved JPEG-compliant bitstream is generated. With non-interleaved format, all encoded pixels of one band precede all encoded pixels of the following band.
Access set-only
Type Xil_boolean
Values TRUE: For images of 4 bands or less, produce an interleaved JPEG-compliant bitstream. FALSE: Produce a noninterleaved JPEG-compliant bitstream.
Default TRUE
HUFFMAN_TABLE
Description Set values in specified Huffman table
Access set-only
Type typedef struct {
int table;
XilJpegHTableType type;
XilJpegHTableValue ∗value;
} XilJpegHTable;
typedef enum {
DC, AC
} XilJpegHTableType;
typedef struct {
int bits;
int pattern;
} XilJpegHTableValue;
Values table: A value in the range 0-3. type: The only valid value is DC. value: A pointer to an array of 17 data pairs, each pair representing a Huffman code. The first element ‘bits’ indicates the length of the Huffman code word. The second element ‘pattern’ contains the actual value of the Huffman code in its least significant ‘bits’ bits. Entry value[k],k=0,16, represents the code for a difference (prediction error) of size category k. See section H.1.2.2 of the Jpeg Specification (ITU Recommendation T.81 - 09/92), for more detail on JpegLL Huffman table specification.
Default By default, the values in each of the tables are pre-initialized to the example values given in Annex K of the ANSI JPEG specification. Tables 0 and 2 contains the same values used to encode DC differences on Jpeg luminance components. Tables 1 and 3 contain the same values used to encode DC differences in Jpeg chrominance components. Both sets of tables are extended to accomodate 16 bit pixel values.
BAND_HUFFMAN_TABLE
Description Instructs the encoder to use a specific Huffman table for a given band.
Access set-only
Type typedef struct {
int band;
int table;
XilJpegHTableType type;
} XilJpegBandHTable;
Values band: Can have a value in the range 0-255. table: A value in the range 0-3. type: The only valid value is DC.
Default Band 0 is encoded with table 0. All other bands are encoded using table 1.
Notes Bands may be assigned to tables that have not yet been set. However, the tables must be set before a call to compress is made or an error occurs.
OPTIMIZE_HUFFMAN_TABLES
Description Provide a hint to the compressor, enabling it to generate optimal Huffman tables instead of using the default example values specified in the ANSI specification. This is only a hint; the compressor is free to ignore the hint. For Lossless JPEG, setting this option attribute on or off keeps the current tables loaded. No optimal Huffman tables are provided for Lossless JPEG.
Access set-only
Type Xil_boolean
Values TRUE: Huffman tables may vary from image to image to achieve higher compression. FALSE: Use fixed Huffman tables for each image in the sequence.
Default FALSE
LOSSLESS_BAND_SELECTOR
Description Associates a band of an image to a predictor selection for the Lossless JPEG compressor. In the following discussion under the Values heading, Px = prediction for pixel "x", A = pixel left, B = pixel above, C = pixel diagonally above and left.
C B
A x
Access set-only
Type typedef struct {
int band;
XilJpegLLBandSelectorType selector;
} XilJpegLLBandSelector;
typedef enum {
ONE_D1,ONE_D2,ONE_D3,TWO_D1,TWO_D2,
TWO_D3,TWO_D4
} XilJpegLLBandSelectorType;
Values band: Can have a value in the range 0-255. NO_PRED: Invalid selection for Lossless JPEG. ONE_D1: Px = A ONE_D2: Px = B ONE_D3: Px = C TWO_D1: Px = A + B - C TWO_D2: Px = A + ((B - C)/2) TWO_D3: Px = B + ((A - C)/2) TWO_D4: Px = (A + B)/2
Default All bands default to selector ONE_D1.
LOSSLESS_BAND_PT_TRANSFORM
Description Associates a band of an image with a point transform, PtTransform, for the Lossless JPEG compressor. If PtTransform is non-zero, the input image band is divided by 2∗∗PtTransform before lossless encoding.
Access set-only
Type typedef struct {
int band;
int PtTransform;
} XilJpegLLBandPtTransform;
Values band: Can have a value in the range 0-255. PtTransform: Can have a value in the range 0-15.
Default All bands default to PtTransform = 0.
EXAMPLES
The following example opens and closes a JPEG Lossless CIS using the XIL library:
XilSystemState State;
XilCis cis;
State = xil_open();
cis = xil_cis_create(State, "JpegLL");
-- calls to JpegLL-specific compression routines --
xil_cis_destroy(cis);
xil_close(State);
The following example sets a JPEG Lossless CIS attribute called ENCODE_INTERLEAVED to TRUE. Note that because this attribute is not a structure, it is not necessary to pass the address of ENCODE_INTERLEAVED when setting it.
XilCis cis;
xil_cis_set_attribute(cis,"ENCODE_INTERLEAVED", (void ∗) TRUE);
The following example returns the value of a JPEG Lossless CIS attribute called ENCODE_INTERLEAVED. Note that when getting an attribute it is always necessary to pass the address.
Xil_boolean encode_type;
XilCis cis;
xil_cis_get_attribute(cis, "ENCODE_INTERLEAVED",
(void ∗∗) &encode_type);
NOTES
The xil_cis_set_attribute () and xil_cis_get_attribute () calls are used to modify the default behavior of a specific compressor. Generic attributes of compressors are set by individual function calls.
SEE ALSO
xil_cis_create(3), xil_cis_get_attribute(3), xil_cis_get_bits_ptr(3), xil_compress(3), xil_decompress(3).
SunOS 5.6 — Last change: 14 April 1993