Re: Wavelet-compressed HRV data


David J Taylor GM8ARV 🏴󠁧󠁢󠁳󠁣󠁴󠁿 🇪🇺
 

But we don't know if these lossless wavelet compressed HRV's are
here to stay. (I really hope so !)

Arne, Eumetsat are looking for any reports of problems with the new
format, so if they don't get any such reports I think the likelihood
of keeping the format increases. If anyone has problems with the
new HRV format please do speak now!!

So I should do a new comparison on lossy compressed HRV's from IMPF
(29 Oct) saved in jpg86 and png.
It would be great to get a good recommendation for the JPEG save
quality I set as default. Of course, the user can alter this to get
either smaller files or a better quality, and it is a subjective
measurement....

Currently I am determining new min/max values on MSG-1 and GOES
images using the 10 bit Rob Alblas XRIT2PIC decoder, will let all
know my results later this week.
First observation: The IMPF system does use the 0..1023 range much
better compared to the IIPS.
The min values should be unchanged, as all MSG-1 channels are
processed so that zero radiance is count 51. That was true of the
IQGSE software and remains true with the IMPF software.

You can set a channel temporarily to min:0, max:1023, gamma: 100,
thermal cal:no to see exactly what range is transmitted. The MSG-1
LRIT channels are already processed with those settings, by the
way.

Given the resulting image histogram then says 13..200 (say), the
corresponding values to set for main and max would be four times
that, 52..800, say. There is no one "correct" setting for gamma.
The value of 140 (gamma = 1.4) is designed so that single count
sensor changes around black level appear as single count image pixel
changes, thus preserving as much of the dynamic range as possible in
the dark parts of the image.

Also beware that when measuring the histogram, the off-earth values
are set to zero rather than the minimum sensor count (this
translates to a value of 1 in the JPEG saved LRIT images I just
checked), so be sure to ignore any histogram values below 13 in
unprocessed images.

Cheers,
David

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