lostpckt Documentation

lostpckt - Find lost packets (dropped compression blocks) in IMP
lostpckt searches for lost packets that contain compression blocks
in a MPF IMP image.  These packets have a signature of 0s in the
blocks.  Currently, there are two types of compression used during
IMP image downlink.  RICE (lossless) and JPEG (lossy).  RICE will
typically be a 1x8 (1 sample, 8 lines) block and JPEG usually
is an 8x8 block.

It has been noted that on some of the JPEG blocks, not all the pixels
are 0s.  Instead, you will see about 2 pixels in the middle with 0s
and then a gradual increase in pixel value three pixels in each
sample direction.  This is typically consistant in the line direction
with the 0s predominately maintained.

Blocks that are found to be part of lost packets are filled with
the ISIS NULL value.

Programmer: Kris Becker, USGS, Flagstaff, Arizona

File name of the cube
to search

NONE

Output file name

--

Number of 0s that must
occur in block in order
for it to be declared
dropped

--

Number of pixels
surrounding a dropped
JPEG block that will be
additionally NULLed

1

Number of pixels
surrounding a dropped
RICE block that will be
additionally NULLed

0

ADDITIONAL NOTES:

Parm	Description
FROM	The name of the input cube file. This file will be searched for dropped packets that evaluate to numerous dropped compression blocks (Default extention is .cub)
TO	The output cube file created by lostpckt. Will be the same pixel type as the input file. (Default extenstion is .cub) Note that this parameter need not be specified. For this case, the blocks that were found will be NULLed out and this result will be written to the output file.
NZEROS	The minimum number of zeros that are required to exist in a block in order for it to be counted as a dropped block. Pixel values of 0 are the signature of dropped data in a given compression IMP block. Some filtering has occured that will fill some of the dropped blocks so, in JPEG cases, not all the pixel values will be 0s. RICE encoding seems to have all 0s in dropped blocks, however. lostpckt will determine the nominal pixels that must exist in a compression block in order for it to be declared a dropped block. This parameter allows the user to provide this value.
JPEGPAD	When filling a JPEG encoded dropped block, extra pixels may need to be NULLed to eliminate the effects of filter bleeding. This value will extend in both sample and line directions the number of pixels NULLed in the output TO image when provided by the user.
RICEPAD	When filling a RICE encoded dropped block, extra pixels may need to be NULLed to eliminate the effects of filter bleeding. This value will extend in both sample and line directions the number of pixels NULLed in the output TO image when provided by the user. Note that RICE encoding usually does not have filtering effects like JPEG does but adding this parameter makes applying padding easier.