Data, Software and More!
Compression Data:
The following file is a .tar archive of all of the compression data I have
collected thus far. When de-tarred, a directory named 'data' appears and the
data files are organized into 'busy', 'sky', and 'atmosphere' subdirectories
(one for each type of image). For each image type, there are data files for
PMEM pages 0-4, each with B values 0, 1, 2, 3, 4, 5, 10, and 15. The first
collumn of each data file contains the name of the image used, the second gives
the compression ratio, and the third gives the rms difference between the
original and the decompressed image. Here's an
example of one of the
data files.
The names of the images listed in the data files conform to the same format.
For example, the image 2.54321.moon.gal.img is a Galileo image of the moon
and has an image entropy of 2.54321.
If you intend to use the data analysis programs from the next section, the directory
'data' should be kept in your home directory and the subdirectory structure
should be left as is.
Download Data Here
Data Analysis Software :
The following are programs I have written to analyze my compression data under IDL.
Each program contains a header with instructions for use.
If you don't want to save each file individually,
Here is
a .tar file containing the following 4 data analysis programs.
read_compression_data.pro
This program reads a compression data file into an IDL array.
This program is required by the following programs!
data_graph.pro
This program plots the best fit lines to the compression data for a given PMEM page,
B value, and image type (busy,sky,atmospheric) and finds the RMS deviation of the data
from the best fit. Optionally, it can also print the best fit equations for the data on
the graph, print the data points as well as the best fit lines, and produce postscript
output.
multi_data_graph.pro
This program plots the best fit lines to compression data for a given PMEM page and image
type with multiple B values, all on the same graph. Useful for assessing the effect of
Increasing B value on compression ratio and data loss. It can optionally produce
postscript output.
plot_vs_b.pro
This program plots the compression data for a given image vs. B value. Postscript output
can be produced.
Compression Related Programs
The following are programs I have written under IDL to calculate image entropy, perform 12:8
compression and 8:12 decompression, deal with the image formats used by the compression
software, write control files for the compression software, calculate the RMS difference
between two images, and read compression ratios from the compression log files. Many of
them have been useful for writing programs to control the compressor via IDL and collect
compression data for large numbers of images.
If you don't want to save each file individually,
Here is
a .tar file containing all of the following programs.
entropy_func.pro
This function returns the image entropy for a given image in IDL. Entropy is calculated in
the manner described in the section on image entropy
conv12to8.pro
,
conv8to12.pro
These programs perform 12:8 compression and 8:12 decompression on an image in
IDL. They require the conversion tables
12to8.dat and 8to12.dat to be placed
in your home directory.
load_codec_image.pro
,
write_for_cod.pro
These programs read and write data between IDL image arrays and files readable by the cod
and decod programs (the Cassini compression simulation software). The image files consist
of a 4 byte header containing the dimensions of the image, followed by 8 bit pixel data.
rms_diff.pro
This program finds the RMS difference between two images. Useful when comparing an original
image to one that has been compressed and decompressed in order to assess the amount of data
lost.
diff_hist2.pro
This program takes rms_diff.pro a few steps further and displays a histogram of the differences
between the corresponding pixels in two different images. Other information, such as maximum
difference, mean difference, and RMS difference is also displayed.
read_compression_log.pro
This program reads a log file generated by the compression software and returns the compression
ratio to an IDL variable.
write_temp_ctl.pro
This program generates a control file for the compression simulation software from IDL.
It accepts an input image name, output image name, PMEM page, and B value. A control
file 'temp.ctl' is generated and can be used for compression and decompression of the
image with the given parameters. It is currently written for 800x800 images, but
can easily be modified for other sizes.
Questions, Comments, Bugs?
If you have any of these, please e-mail me at
obrien@astrosun.tn.cornell.edu.
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