2160p HDR to 1080p HDR

[Erikk64]

hi 
again

i recently did an encoding from 2160p to 1080p hdr ,and the result was a slightly different color..





did i miss something or should i expect results from dimension reduction
also , i did the following:
enable hdr + cll and fall from input + resize method 9-lanczos

and i missed those :
enable hdr opt
enable master display


..
the source MediaInfo 
Color range                              : Limited
Color primaries                          : BT.2020
Transfer characteristics                : PQ
Matrix coefficients                      : BT.2020 non-constant
Mastering display color primaries        : Display P3
Mastering display luminance              : min: 0.0050 cd/m2, max: 4000 cd/m2
Maximum Content Light Level              : 10000 cd/m2
Maximum Frame-Average Light Level        : 596 cd/m2
Original source medium                  : Blu-ray

the result:
Bit rate                                : 18.0 Mb/s
Width                                    : 1 920 pixels
Height                                  : 1 080 pixels
Display aspect ratio                    : 16:9
Frame rate mode                          : Constant
Frame rate                              : 23.976 (24000/1001) FPS
Color space                              : YUV
Chroma subsampling                      : 4:2:0
Bit depth                                : 10 bits
Bits/(Pixel*Frame)                      : 0.362

Color range                              : Limited
Color primaries                          : BT.2020
Transfer characteristics                : PQ
Matrix coefficients                      : BT.2020 non-constant
Maximum Content Light Level              : 10000 cd/m2
Maximum Frame-Average Light Level        : 596 cd/m2

[Selur]

Yes, changing the resolution will (expectedly) at least somehow change the color perception.

Note that your way of comparing the colors might be flawed.
Depending on the player and the used video renderer, opening multiple instances might produce different color handling.
You might want to check whether the displayed colors change, if you open the files in a different order.

Personally, I would
a. open the files in a Vapoursynth script (without the HDR data) for comparison. (assuming the hdr metadata are the same, one can ignore them for comparing)
b. not use Lanczos, but SSIM, DPID, ResampleHQ or Spline64 for down scaling. (not sure whether they all work fine on HDR content)

Not knowing what you really did in Hybrid, I doubt this is a bug.

Cu Selur

[Erikk64]

(not use Lanczos, but SSIM, DPID, ResampleHQ or Spline64 for down scaling.)


i also tried this ,but the result was the same

[Selur]

No clue whether the HDR2SDR routine you use does anything different when confronted with HDR on HD content.
Does the Vapoursynth Preview also show the color change?

Cu Selur

[Selur]

Do these files show different colors for you?
(I uploaded a UHD HDR test file and re-encoded it to a HD HDR test file.)
=> https://www.mediafire.com/folder/j415iw3euq43k/HDR+Test
(they show no real color difference for me on my HDR display)

Cu Selur

[Erikk64]

no




I don't remember exactly
Because I did a lot of things and made many attempts
Then I deleted the files to save space


But I started asking because I got frustrated and expected that I made a mistake in something I haven't noticed yet

[Selur]

Since you didn't read the sticky, I have no clue what you did.
You can use the Vapoursynth Preview to see whether the resizing does change the colors (without the HDR data).
On reencoding, you should make sure that the signaling is set properly.
Can't reproduce the problem, so my guess is that you made some mistake in whatever you did.

Cu Selur

[Erikk64]

Yeah, haha,

I really thought about giving up on the idea completely, but my mind is still insisting. I'll give this matter more time later with some digging.

[Selur]

Do that, also use the latest dev, this way you are sure you used the same version I used for my test.

Cu Selur