Remap RGB value range to HDR?

[eobet]

For some quick and dirty photo matching 3D renders, I just bash a background photo onto a equirectangular layout and save it out as a HDR. This enables me to import it into a 3D application and use it for fake environmental lighting and reflections.

However, sometimes the lighting comes out really flat, even though it's quite a high contrast photo. The reason is of course that the RGB colors in the photo doesn't have any values that extend in the HDR range.

Is there a way to fake this? Is there a way to boost RGB colors into the HDR range in Affinity Photo? I tried with Gamma & Exposure in the 32-bit preview panel, but that's just a preview, isn't it?

[James Ritson]

24 minutes ago, eobet said:

For some quick and dirty photo matching 3D renders, I just bash a background photo onto a equirectangular layout and save it out as a HDR. This enables me to import it into a 3D application and use it for fake environmental lighting and reflections.

However, sometimes the lighting comes out really flat, even though it's quite a high contrast photo. The reason is of course that the RGB colors in the photo doesn't have any values that extend in the HDR range.

Is there a way to fake this? Is there a way to boost RGB colors into the HDR range in Affinity Photo? I tried with Gamma & Exposure in the 32-bit preview panel, but that's just a preview, isn't it?

Hi @eobet, if you're just taking SDR-encoded images and using them as a lighting model, it almost seems pointless encoding them in an HDR format—I think the majority of 3D authoring software lets you use SDR-encoded formats as well? (With the understanding that lighting will be substandard)

However, if you want to artificially expand the range into HDR, you could convert your document to 32-bit HDR using Document>Convert Format / ICC Profile. This will convert the values to floating point, with 0-1 being the range for SDR values.

What you could then do is add an Exposure adjustment and push the exposure up linearly for all pixel values—try +1 or +2 to start. You could then use a Brightness / Contrast adjustment and bring the brightness down and also experiment with the contrast. The Brightness / Contrast adjustment only works on the 0-1 range of pixels, so you leave the HDR >1 pixels as they are. This would allow you to artificially expand the dynamic range of the scene.

The Curves adjustment, by default, also works between 0-1, so you could also use this to manipulate contrast of just the 0-1 SDR pixel values. However, on the Curves dialog, you can set the min/max values—so you can use a max greater than 1 and it will now also affect HDR values.

Then of course you would export to OpenEXR or Radiance HDR and bring that into your 3D software.

The 32-bit Preview Panel options are purely for the final display presentation only, so as you've discovered they will not modify the pixel values in your document at all. If you have an HDR/EDR display you can enable HDR/EDR preview to see pixel values >1. Otherwise, you can move the Exposure slider down to see those bright values.

Hope the above helps!

[eobet]

Thank you for the detailed explanation!

I will experiment with this.