TITLE:
Perceptually Lossless Compression for Mastcam Multispectral Images: A Comparative Study
AUTHORS:
Chiman Kwan, Jude Larkin
KEYWORDS:
Perceptually Lossless Compression, Mastcam Images, JPEG, J2K, X264, X265, Daala, Multispectral, PCA, Video Compression
JOURNAL NAME:
Journal of Signal and Information Processing,
Vol.10 No.4,
November
28,
2019
ABSTRACT: The two mast cameras, Mastcams, onboard Mars rover
Curiosity are multispectral imagers with nine bands in each. Currently, the
images are compressed losslessly using JPEG, which can achieve only two to
three times of compression. We present a comparative study of four approaches
to compressing multispectral Mastcam images. The first approach is to divide
the nine bands into three groups with each group having three bands. Since the
multispectral bands have strong correlation, we treat the three groups of
images as video frames. We call this approach the Video approach. The second
approach is to compress each group separately and we call it the split band
(SB) approach. The third one is to apply a two-step approach in which the first
step uses principal component analysis (PCA) to compress a nine-band image cube
to six bands and a second step compresses the six PCA bands using conventional
codecs. The fourth one is to apply PCA only. In addition, we also present
subjective and objective assessment results for compressing RGB images because
RGB images have been used for stereo and disparity map generation. Five
well-known compression codecs, including JPEG, JPEG-2000 (J2K), X264, X265,
and Daala in the literature, have been applied and compared in each approach.
The performance of different algorithms was assessed using four well-known
performance metrics. Two are conventional and another two are known to have
good correlation with human perception. Extensive experiments using actual Mastcam images have been performed to
demonstrate the various approaches. We observed that perceptually lossless
compression can be achieved at 10:1 compression ratio. In particular, the
performance gain of the SB approach with Daala is at least 5 dBs in terms peak
signal-to-noise ratio (PSNR) at 10:1 compression ratio over that of JPEG.
Subjective comparisons also corroborated with the objective metrics in
that perceptually lossless compression can be achieved even at 20 to 1
compression.