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

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

      This data set uses the Committee on Data Management and
      Computation (CODMAC) data level numbering system. The MSL
      MAHLI 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,
      2 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).


      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 2 zstack data types (1 image, 1 thumbnail) 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, MAHLI 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.

      Focus merge images are always JPEG 444 color images based on
      the 2 to 8 source images.

      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 produced 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 a smaller
      image which is then JPEG compressed.  The extraction of these
      coefficients is the only way MAHLI images are ever sub-sampled.

      The following is a table of the different zstack product types 
      generated by MAHLI which are contained within the raw camera 
      data record. 
 
      Type  Product                 Format     Pixel bits
      -----------------------------------------------------
      R     Focus Merge Image       JPEG 444   48
      T     Focus Merge 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 MAHLI data
      products and RDR processing.

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