Re: [EXTERNAL] Re: Conformance files in PQ, HLG, SDR-BT.709?

Hi all,

Finally had a play with the PNG Chunk program you linked.

One item we may need to address is that it seems to me to be possible using that program to create a PNG file with sRGB, cHRM, iCCP and cICP chunks, all with different primary chromaticities.

I think we need to check that this is correctly dealt with in the specification and in any conformance checks.  I’m checking with colleagues about how known incorrect test files are usually issued – we don’t want people to assume that because a file is available in the conformance set, it is valid.

Best regards

Simon


Simon Thompson
Senior R&D Engineer

BBC Research & Development


From: Simon Thompson - NM <Simon.Thompson2@bbc.co.uk>
Date: Thursday, 7 December 2023 at 11:19
To: Chris Blume (ProgramMax) <programmax@gmail.com>, Seeger, Chris (NBCUniversal) <Chris.Seeger@nbcuni.com>
Cc: Portable Network Graphics (PNG) Working Group <public-png@w3.org>
Subject: Re: [EXTERNAL] Re: Conformance files in PQ, HLG, SDR-BT.709?
Hi all,

Would it be useful to have a table which lists the test files, the chunks present and what the expected behaviour is (and is not).

(Also, being slightly pedantic, but in the release notes we may have to explain what is meant by a BT.709 CICP with the Full Range Video Flag set as there is no full range in BT.709)

Best Regards

Simon


Simon Thompson
Senior R&D Engineer

BBC Research & Development


From: Chris Blume (ProgramMax) <programmax@gmail.com>
Date: Wednesday, 6 December 2023 at 23:23
To: Seeger, Chris (NBCUniversal) <Chris.Seeger@nbcuni.com>
Cc: Portable Network Graphics (PNG) Working Group <public-png@w3.org>
Subject: Re: [EXTERNAL] Re: Conformance files in PQ, HLG, SDR-BT.709?

External: Think before clicking
I'm not sure why the PQ image has transfer function 22 and the HLG narrow has 24.
Is the HLG full also 24? Is it behaving correctly?

I'm happy to work alongside Jerome to figure it out if they want to email me directly.
I checked the files again and they should be good.
Given that the values should have been 16 and 18, it sounds like 6 is somehow being added to those values.

On Wed, Dec 6, 2023 at 6:15 PM Seeger, Chris (NBCUniversal) <Chris.Seeger@nbcuni.com<mailto:Chris.Seeger@nbcuni.com>> wrote:
Jerome also said:

“PNG-PQ-BT.2111-ColorBars-16bit-CICP-FR.png has Transfer Function of 22 and PNG-HLG-FancyColorBars-16bit-CICP-NR.png has Transfer Function of 24”

Do you know why this would be?

-Chris

From: Chris Blume (ProgramMax) <programmax@gmail.com<mailto:programmax@gmail.com>>
Date: Wednesday, December 6, 2023 at 6:13 PM
To: Seeger, Chris (NBCUniversal) <Chris.Seeger@nbcuni.com<mailto:Chris.Seeger@nbcuni.com>>
Cc: Portable Network Graphics (PNG) Working Group <public-png@w3.org<mailto:public-png@w3.org>>
Subject: Re: [EXTERNAL] Re: Conformance files in PQ, HLG, SDR-BT.709?
(Oh, the files are already named "SDR-BT.709" and not just "SDR". So the file names are fine.)

On Wed, Dec 6, 2023 at 6:07 PM Chris Blume (ProgramMax) <programmax@gmail.com<mailto:programmax@gmail.com>> wrote:
I'm creating those .chunk files now.
But I realized a potential mistake I made in the batch of 5 images I sent you.

You provided the correct CICP values and I blindly copied them. However, they need to be adapted for PNG.
PNG currently only supports the identity matrix. So the third field should always be 0.

Values I used:
SDR CICP: 1-1-1
PQ CICP: 9-16-9
HLG CICP: 9-18-9

Values I should have used:
SDR CICP: 1-1-0
PQ CICP: 9-16-0
HLG CICP: 9-18-0

(Also, I want to rename the file from "SDR" to "BT709". I'll also create an sRGB file.)

Will these CICP values be a problem for your testing? Should we revisit the CICP chunk to allow non-zero matrix coefficients?

On Wed, Dec 6, 2023 at 5:42 PM Seeger, Chris (NBCUniversal) <Chris.Seeger@nbcuni.com<mailto:Chris.Seeger@nbcuni.com>> wrote:
I’ve sent the example files to MediaArea to see if they can add detection to MediaInfo.

From: Seeger, Chris (NBCUniversal) <Chris.Seeger@nbcuni.com<mailto:Chris.Seeger@nbcuni.com>>
Date: Wednesday, December 6, 2023 at 5:41 PM
To: Chris Blume (ProgramMax) <programmax@gmail.com<mailto:programmax@gmail.com>>
Cc: Portable Network Graphics (PNG) Working Group <public-png@w3.org<mailto:public-png@w3.org>>
Subject: Re: [EXTERNAL] Re: Conformance files in PQ, HLG, SDR-BT.709?
Hi Chris,

Do you have the raw cicp.chunk files with each value (of the 6 variations).  We can use them to change future files.

Thx.

From: Chris Blume (ProgramMax) <programmax@gmail.com<mailto:programmax@gmail.com>>
Date: Wednesday, December 6, 2023 at 5:12 PM
To: Seeger, Chris (NBCUniversal) <Chris.Seeger@nbcuni.com<mailto:Chris.Seeger@nbcuni.com>>
Cc: Portable Network Graphics (PNG) Working Group <public-png@w3.org<mailto:public-png@w3.org>>
Subject: Re: [EXTERNAL] Re: Conformance files in PQ, HLG, SDR-BT.709?
Attached are the 5 images with the CICP values you provided. I changed the file names so the "NoCICP" part is now just "CICP".

I'm also attaching a file named cicp.chunk. This simplifies if we want to add cICP chunks to other PNGs in the future. Here is how:
The cicp.chunk file has the CICP values 0-0-0-0. You can use a hex editor like HexEd.it<https://urldefense.com/v3/__http:/HexEd.it__;!!PIZeeW5wscynRQ!ojwrBR6jR3-svspWLLmi1N_ZGz0nu2iGkJRX82x3p2CR9ElYZ4ANFsR04-MBHxq5KizMxgWA4AwDvSxkTFCy$> to open the cicp.chunk file and change the last 4 bytes to different CICP values. Save your changes.
Then, with TweakPNG<https://urldefense.com/v3/__https:/entropymine.com/jason/tweakpng/__;!!PIZeeW5wscynRQ!ojwrBR6jR3-svspWLLmi1N_ZGz0nu2iGkJRX82x3p2CR9ElYZ4ANFsR04-MBHxq5KizMxgWA4AwDvZ-Skuci$>, you can use the menu Edit -> Import Chunk... and select the cicp.chunk file. This will add the cICP chunk to the PNG you have open.

It is a bit of a pain to need to manually edit the cicp.chunk file every time. But the benefit of using this approach is you don't need to manually compute the chunk's CRC values, since TweakPNG will add them for you.
Also, since this process is a pain I'm happy to do this for people in the future.

Hope this helps :D

On Wed, Dec 6, 2023 at 1:57 PM Seeger, Chris (NBCUniversal) <Chris.Seeger@nbcuni.com<mailto:Chris.Seeger@nbcuni.com>> wrote:
I haven’t made contact with Pixelmator folks yet. But here are the Affinity Folks.

I’m corresponding with:

Andy Somerfield asomerfield@serif.com<mailto:asomerfield@serif.com> (dev)
John Atkin john@serif.com<mailto:john@serif.com> (PR)

This is what Andy shared so far:

Internally, Photo manipulates HDR content as ICC profiled, linear 32bit floating point data. Conversion from PQ / HLG is dealt with at import time (for example, a PQ encoded HEIF from a Canon camera will be converted to Linear sRGB).

All compositing is then done in a linear colour space and we support a number of clipping visualisation options as well as native HDR display (which is presently a bit better on Mac than Windows - Apple’s approach to HDR display is the right approach, but others are yet to properly copy it). A large number of (nearly all) Photo features work properly in 32bit HDR - aside from the obvious (Invert, etc. where there is no logical “Maximum”).

We currently do not support encoding to PQ / HLG at export time - although it’s something we are actively looking to do. I guess we are waiting for the format war to conclude (or rather, to begin..)

Our 32bit compositing pipeline was developed primarily for VFX users - so our EXR round-trip stuff is pretty good - but that’s not what you’re looking for, I assume.

-Chris


From: Chris Blume (ProgramMax) <programmax@gmail.com<mailto:programmax@gmail.com>>
Date: Wednesday, December 6, 2023 at 1:45 PM
To: Seeger, Chris (NBCUniversal) <Chris.Seeger@nbcuni.com<mailto:Chris.Seeger@nbcuni.com>>
Cc: Portable Network Graphics (PNG) Working Group <public-png@w3.org<mailto:public-png@w3.org>>
Subject: Re: [EXTERNAL] Re: Conformance files in PQ, HLG, SDR-BT.709?
Do we have contacts at either of those two companies?

On Wed, Dec 6, 2023 at 12:39 PM Seeger, Chris (NBCUniversal) <Chris.Seeger@nbcuni.com<mailto:Chris.Seeger@nbcuni.com>> wrote:
Thanks so much 😊. This will move us forward more quickly.

Two new apps to test that might be worth some more investigation:

Photomator
https://apps.apple.com/us/app/photomator-photo-editor/id1444636541<https://urldefense.com/v3/__https:/apps.apple.com/us/app/photomator-photo-editor/id1444636541__;!!PIZeeW5wscynRQ!p_ez9avjNcZUjumErOtECBA-lsR2cn4LVb2Y1Z2g_SZ18aSceD1onLjF28JZsu_85wsz__0QELd90TshvzdG$>

Affinity Photo
https://apps.apple.com/us/app/affinity-photo-2/id1616822987?mt=12<https://urldefense.com/v3/__https:/apps.apple.com/us/app/affinity-photo-2/id1616822987?mt=12__;!!PIZeeW5wscynRQ!p_ez9avjNcZUjumErOtECBA-lsR2cn4LVb2Y1Z2g_SZ18aSceD1onLjF28JZsu_85wsz__0QELd90REW-68w$>


Best,
Chris

From: Chris Blume (ProgramMax) <programmax@gmail.com<mailto:programmax@gmail.com>>
Date: Wednesday, December 6, 2023 at 11:52 AM
To: Seeger, Chris (NBCUniversal) <Chris.Seeger@nbcuni.com<mailto:Chris.Seeger@nbcuni.com>>
Cc: Portable Network Graphics (PNG) Working Group <public-png@w3.org<mailto:public-png@w3.org>>
Subject: Re: [EXTERNAL] Re: Conformance files in PQ, HLG, SDR-BT.709?
Simon is right.
I'll work on adding cICP chunks now.

On Wed, Dec 6, 2023 at 11:11 AM Seeger, Chris (NBCUniversal) <Chris.Seeger@nbcuni.com<mailto:Chris.Seeger@nbcuni.com>> wrote:
Yes.  They are public. Can we start with cicp only as they are not required for PQ, HLG or SDR?

If you show me how to do it, and with what tools, maybe I can help.

Best,
Chris

Get Outlook for iOS<https://urldefense.com/v3/__https:/aka.ms/o0ukef__;!!PIZeeW5wscynRQ!uLCseTAx_Hyxx7ImY4JuTY9ZQE6yQqk9WuV4Jp7w5pOovkCOED_tSs63dlwwyry1KgwghWlvJWWUJ5s7UYwx$>
________________________________
From: Chris Blume (ProgramMax) <programmax@gmail.com<mailto:programmax@gmail.com>>
Sent: Wednesday, December 6, 2023 10:37:11 AM
To: Seeger, Chris (NBCUniversal) <Chris.Seeger@nbcuni.com<mailto:Chris.Seeger@nbcuni.com>>
Cc: Portable Network Graphics (PNG) Working Group <public-png@w3.org<mailto:public-png@w3.org>>
Subject: [EXTERNAL] Re: Conformance files in PQ, HLG, SDR-BT.709?

I can hexedit in cICP values.

Although, maybe I should wait until we have mDCv and cLLi values as well? How long do you think it would take to get those values?

My thought is: I don't want to start distributing test images only to later tell people to use these new test images instead (when they don't yet have a way to see which ones are new/old).
But maybe it will take a while to get mDCv and cLLi values. So maybe it would be good to get some new test images sooner?

(Are these images public domain? Can we distribute them widely?)

On Wed, Dec 6, 2023 at 8:53 AM Seeger, Chris (NBCUniversal) <Chris.Seeger@nbcuni.com<mailto:Chris.Seeger@nbcuni.com>> wrote:

Hi Chris and All,



Do we have any conformance files in each format (PQ, HLG, SDR-BT.709)? I’ve got a number of developers who’d like to add the functionality into their apps. Once of them requested test files.



I’ve created test files if someone can add cICp chunks to them:



https://www.dropbox.com/scl/fo/a44vfxw3p21kvkh8nywpc/h?rlkey=v63ekq5y49kd4omg59ng9q3zr&dl=0<https://urldefense.com/v3/__https:/www.dropbox.com/scl/fo/a44vfxw3p21kvkh8nywpc/h?rlkey=v63ekq5y49kd4omg59ng9q3zr&dl=0__;!!PIZeeW5wscynRQ!u3P4S_qNlSUgxiBGGql3lAci2mnjiYXwiMFO_BJmTverJdmVa01jIZup7LNb0VmqqIefc7ZiC_qDHR576Lqb$>



SDR CICP: 1-1-1 (Narrow and Full Range versions marked NR or FR)

PQ CICP: 9-16-9 (Full Range only as there is no benefit to NR PQ)

HLG CICP: 9-18-9 (Narrow and Full Range versions marked NR or FR)



I will send mDCv and cLLI values (just an example at a later date since cICp is most important to get to developers).



Thanks very much,



Chris Seeger

Director, Advanced Content Production

Office of the CTO

C: 551-238-3768

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