[SLS-DC] [EXTERNAL] Re: 123B2 Corrigendum
Kiely, Aaron B (US 332B)
aaron.b.kiely at jpl.nasa.gov
Wed Aug 4 17:17:05 UTC 2021
Hi Everyone,
Happily, Ian is correct and no change is needed to the Blue Book. Hopefully this incident can serve as a cautionary reminder of just how dangerous it is to spend too many hours staring at the Green Book.
Mark, when D=3, the test for setting the value of k can never produce a value of k=2 (see Annex F of the Green Book). It can produce a value of k=1, but the standard does not allow it. So all samples for an image with D=3 will be encoded as low-entropy samples. Performance would be better if we allowed k=1 in this case, but that would be one more code option to implement for negligible benefit.
Aaron
> On Aug 4, 2021, at 7:48 AM, Wong, Englin (GSFC-5670) <mark.wong at nasa.gov> wrote:
>
> Hi Aaron,
>
> Is it correct to assume for D=3 case defined in current definition k_z(t)=2, although rare, the compression is not optimal under the high entropy mode? Or, possibly not compressing?
> I agree with the changes proposed to put D=3 to be all low entropy samples if high entropy condition is rare. Also, I agree the note in 5.4.3.3.5.1.4 needs to be updated as well.
>
> Best,
> Mark Wong
> NASA GSFC Flight Microwave & Telecommunication Systems Branch
> Phone: 1-301-286-6549
>
> From: SLS-DC <sls-dc-bounces at mailman.ccsds.org> On Behalf Of Gian.Paolo.Calzolari at esa.int
> Sent: Wednesday, August 4, 2021 4:26 AM
> To: Roberto.Camarero at esa.int
> Cc: sls-dc at mailman.ccsds.org; SLS-DC <sls-dc-bounces at mailman.ccsds.org>
> Subject: [EXTERNAL] Re: [SLS-DC] 123B2 Corrigendum
>
> Just an hint.
> We have already a Technical Corrigendum 3 to CCSDS 123.0-B-2, Issued February 2019 and I fear the (unwritten) rule is that 3 is the maximum number of corrigenda.
> Therefore you better check with Tom (cc'ed here) about this.
>
> CIao
>
> Gian Paolo
> (Not AD :o)
>
>
>
> From: Roberto.Camarero at esa.int <mailto:Roberto.Camarero at esa.int>
> To: "Kiely, Aaron B (US 332B)" <aaron.b.kiely at jpl.nasa.gov <mailto:aaron.b.kiely at jpl.nasa.gov>>
> Cc: "sls-dc at mailman.ccsds.org <mailto:sls-dc at mailman.ccsds.org>" <sls-dc at mailman.ccsds.org <mailto:sls-dc at mailman.ccsds.org>>
> Date: 04-08-21 09:52
> Subject: Re: [SLS-DC] 123B2 Corrigendum
> Sent by: "SLS-DC" <sls-dc-bounces at mailman.ccsds.org <mailto:sls-dc-bounces at mailman.ccsds.org>>
>
>
>
> Dear Aaron, dear all,
>
> Good catch Aaron.
> My only question would be if we are not missing a definition for t>0 and D=3 in that case, in which k_z(t)=1 should be used according to Annex F in the Green Book.
> If not, I understand that by this change we force D=3 samples to be encoded with low entropy codes only. In that case we should probably also change Annex F and the Note in 5.4.3.3.5.1.4 to "When D<=3, the condition...".
>
> Kind regards,
>
> Roberto
>
>
>
>
> ESA – European Space Agency
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> Onboard Payload Data Processing Engineer
> TEC-EFD / Electrical Engineering Department
> ESTEC
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> From: "Kiely, Aaron B (US 332B)" <aaron.b.kiely at jpl.nasa.gov <mailto:aaron.b.kiely at jpl.nasa.gov>>
> To: "sls-dc at mailman.ccsds.org <mailto:sls-dc at mailman.ccsds.org>" <sls-dc at mailman.ccsds.org <mailto:sls-dc at mailman.ccsds.org>>
> Date: 08/04/2021 12:52 AM
> Subject: [SLS-DC] 123B2 Corrigendum
> Sent by: "SLS-DC" <sls-dc-bounces at mailman.ccsds.org <mailto:sls-dc-bounces at mailman.ccsds.org>>
>
>
>
> Dear Working Group,
>
> There is a minor issue with 123B2.
>
> The NOTE in 5.4.3.3.5.2 of 123B2 states that, “For high-entropy samples, it can be shown that k_z(t)>=2.” In fact, as the standard is written this isn’t true, it’s just extremely rare – it can only happen when bit depth is D=3. (See Annex F of the Green Book.)
>
> We intended for the idea of this note to be normative, eliminating the need to implement a code that would be used only for a very special case. I believe we should request a corrigendum to do the following:
> 1. In 5.4.3.3.5.2, change
> k_z(t) is the largest positive integer k_z(t)<=max{D-2,2}, such that…
> to
> k_z(t) is the largest integer 2<=k_z(t)<=max{D-2,2}, such that…
> 2. Delete the NOTE in 5.4.3.3.5.2.
> 3. In 5.4.3.3.5.1.4, change
> For t>0…
> to
> For t>0 and D>3, …
>
> Please let me know if this looks right, and if we have consensus I’ll forward this to the Editor and Area Director.
>
> Thanks,
> Aaron[attachment "smime.p7s" deleted by Roberto Camarero/estec/ESA]
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