How to make an HDR test image with text so bright!

[pomesio]

Hi all

I don't quite remember where I saw it, it was a normal pure white image when displayed on SDR screen, but the text "HDR" reveals when displayed on HDR screen O_O, I'm trying to replicate it but it turns out harder than I thought!

I tried set the background to 100 nits, and the words to 4000 nits, after I exported it to tiff with Rec2020 PQ 1000 nits, and I displayed it on my SDR screen, I think the system software tone mapped it to an acceptable level, so the background looks darker, and the text is pure white. What I want is to clip the brightness that are above the max brightness of the SDR screen, any ideas?

BTW I'm using Davinci resolve.

[RealNC]

It was probably an image with a gain map. Those images are basically two images in the same file. One is SDR, one is HDR. The HDR image is generated by the gain map.

AVIF supports gain maps. UltraHDR does as well (UltraHDR is based on JPEG.) There might be other formats that support this as well, not sure. You need software that can create gain maps. In such software, you supply two images, one is SDR and one is HDR. The software then uses those to generate a gain map. As a result, on SDR displays, the SDR image will be displayed. On HDR displays, the HDR version of the image is generated by applying the game map on top of the SDR image.

To create an image like the one you described, you would simply put the text "SDR" in the SDR image, and "HDR" into the HDR image. Then export then as a single gain map image. Obviously the software that is used to view the image must support gain maps. Most browsers do.