Data Set Overview
      =================

      This data set contains image products acquired by the MARDI 
      instrument.

      This data set uses the Committee on Data Management and 
      Computation (CODMAC) data level numbering system. The MSL 
      MARDI RDRs are considered Level 4 or Resampled.  The RDRs 
      are created from EDR images and contain irreversibly 
      transformed data due to the nature of JPEG decompression.

      Processing
      ==========

      After extracting and decompressing (if needed) EDR products,
      4 RDR products are created for each EDR.  These are
      generated from validated data. The products are:

      (1) decompressed and radiometrically calibrated (16-bit),
      (2) decompressed, radiometrically calibrated, and color corrected
          (8-bit),
      (3) decompressed, radiometrically calibrated, and geometrically
          linearized (16-bit), and
      (4) decompressed, radiometrically calibrated, color corrected,
          and geometrically linearized (8-bit).


      Data
      ====

      The RDRs produced have detached PDS-compliant labels.
      The Mast Camera (Mastcam), Mars Hand Lens Imager (MAHLI),
      and Mars Descent Imager (MARDI) Experiment Data Record (EDR)
      and Reduced Data Record (RDR) PDS Data Products Software
      Interface Specification contains a detailed description of the
      RDR formatted products.

      There are 9 image data types (6 images, 3 thumbnails) that can be 
      wrapped into the original data format that is transferred from 
      the cameras. Some of these are compressed in a format which can 
      reproduce an image identical to the original image on the 
      instrument (lossless compression), some are transferred in lossy 
      format, some are full-scale and others sub-sampled (the only sub-
      sampled is by a factor of 8, used to produce thumbnail images). 
      The RDR data file includes the camera mini-header generated by
      the camera, followed by original image data as formatted by the 
      camera.

      Not including sub-framing, MARDI can take a variety of image data
      formats and accomplish this by internal processing. The cameras 
      always acquire raw 12-bit data. Normally, the 12-bit raw data
      are converted from 12-to-8-bits through the use of a variety
      of companding (compress/expand) lookup tables, the most generally 
      used being a modified square-root encoding scheme that allocates 
      additional values to low DNs. These companded 8-bit images can 
      then be processed either immediately, and stored into each 
      camera's 8-Gbyte buffer, or they can be stored unprocessed in the
      buffer, and then later processed in response to downlink commands.
      It is this flexibility that leads to the complexities of the raw
      data format and its description.

      In addition to the 12-to-8-bit companding, on-board processing
      includes the following capabilities: Bayer pattern interpolation,
      lossless compression, and JPEG compression. Except for thumbnails,
      the cameras do not support sub-sampling or resampling, but do 
      support sub-framing.

      Thumbnails are created by creating a scratch JPEG image, and 
      extracting the lowest order coefficients of the discrete cosine
      transform 8x8 pixel compression block, or minimum compression unit
      (MCU), which is essentially the average of the 8x8 spatial domain
      MCU. These coefficients are then assembled into an 1/8th sized 
      image, and can then themselves be JPEG compressed. The extraction
      of these coefficients is the only way MARDI images can be 
      sub-sampled.

      The following is a table of the different image product types 
      generated by MARDI which are contained within the raw camera data 
      record. 
 
      Type  Product     Format     Pixel bits
      -----------------------------------------------------
      A     Image       Raster     48
      B     Image       Raster     48
      C     Image       Lossless   48
      D     Image       JPEG gray  16
      E     Image       JPEG 422   48
      F     Image       JPEG 444   48
      G     Thumbnail   Raster     16
      H     Thumbnail   JPEG gray  16
      I     Thumbnail   JPEG 444   48


      Refer to the Mast Camera (Mastcam), Mars Hand Lens Imager (MAHLI),
      and Mars Descent Imager (MARDI) Experiment Data Record (EDR)
      and Reduced Data Record (RDR) PDS Data Products Software
      Interface Specification for further details on the MARDI data
      products and RDR processing.

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