Converted SDR image from HDR looks darker.

[SYama6142]

Hello,

I'm developing an encoder software with Intel VPL with HDR support.

I followed this instruction to implement HDR to SDR conversion.

https://intel.github.io/libvpl/latest/programming_guide/VPL_prg_vpp.html#hdr-tone-mapping

I tested conversion but the image looks darker compared with the original.

I also tested with ffmpeg and same issue happens. Here's the code.

# No color space change (HDR_image.png)
ffmpeg -init_hw_device qsv=qsv_device:0 -filter_hw_device qsv_device -hwaccel qsv -hwaccel_output_format qsv -i <INPUT.mp4> -c:v hevc_qsv -profile:v main10 -preset 1 -async_depth 4 -low_power 1 -b:v 12M -maxrate:v 12M -g 90 -color_primaries bt2020 -color_trc smpte2084 -colorspace bt2020nc -color_range tv <OUTPUT.mp4>
# HDR to SDR conversion using VPP (SDR_image.png)
ffmpeg -init_hw_device qsv=qsv_device:0 -filter_hw_device qsv_device -hwaccel qsv -hwaccel_output_format qsv -i <INPUT.mp4> -c:v hevc_qsv -profile:v main -preset 1 -async_depth 4 -low_power 1 -b:v 12M -maxrate:v 12M -g 90 -color_primaries bt709 -color_trc bt709 -colorspace bt709 -color_range tv <OUTPUT.mp4>
# HDR to SDR conversion using tonemap filter (SDR_tonemap_image.png)
ffmpeg -i <INPUT.mp4> -c:v hevc_qsv -profile:v main -b:v 12M -maxrate:v 12M -g 90 -vf zscale=t=linear:npl=100,format=gbrpf32le,zscale=p=bt709,tonemap=tonemap=hable:desat=0,zscale=t=bt709:m=bt709:r=tv,format=yuv420p <OUTPUT.mp4>

I thought that VPP remaps tone during conversion, but it does not do?

If it is true, I have to think about adding some library...