Dynamic Range and HDR question(s)?

[Marcus Friedlander]

Hi everyone!

I have a question about dynamic range in relation to HDR mode. Do you need to exactly match DR for a whole scene (much in the same way you would match lighting on set or coloring in post) in order to maintain continuity? Can the human eye notice the difference between different shots cut together with different Dynamic Ranges? For instance, if I was shooting a basic shot reverse shot scene, and one of the actors had their backs to a window, could i put on HDRx 4 to give me 20.5 stops of DR and then intercut it with the reverse shot which would be shot normally with 16.5 stops of DR? Or would I also need to do HDRx 4 on the reverse shot to bring them both up to 20.5 stops of DR.

Thanks in advanced for any answer answers, tips, or advice!

 

[Burke Doeren]

Marcus, from what I've seen in my own work, HDRx currently works as a sort of luma key, where any blown out information from the A-Track is replaced by info from the X-Track.

You really only benefit (dynamic range wise) from using HDRx if you have a bright source in your frame that is clipping, otherwise, the difference is not really noticeable.

I actually use HDRx quite a bit for bright practical lights and windows, and I found that HDRx + 3 works like a dream. It seems to be the perfect hand off of color tones and luminance values between A and X tracks.

When you activate HDRx in REDCINE-X PRO or Davinci, your perceived brightness value of your image will get darker, but you can always use FLUT or ISO to boost it back up so your A-track has the original brightness you intended, and your X-track just fills in the bright details. Boosting FLUT or ISO after turning on HDRx will not add noise like you may think it would, it just re-balances the middle gray because HDRx seems to shift it by adding all the new highlight stops.

Also, as far as perception goes, if you just use HDRx and a normal toolset for grading (i.e. no tone-mapping) your results will feel very normal and not jarring from one shot to the next. If handled properly, you can get some brilliant results. HDRx was actually used quite a bit on Netflix's House of Cards to fill bright window detail.

 

[Marcus Friedlander]

Thanks for the response Burke! I have a couple of follow up questions if you don't mind.

1. "HDRx currently works as a sort of luma key, where any blown out information from the A-Track is replaced by info from the X-Track." Is there anyway to do the opposite of this? Can the X-track be used to save the shadow detail instead? If not do you recommend exposing for the shadow in the A-track and saving the highlights in the X-track? If that's true, then the further you under expose the A-track (assuming you still have a reasonable exposure) the more dynamic range you can "force" into the image, correct? And more dynamic range GENERALLY equals a more pleasing image correct?

2. "I found that HDRx + 3 works like a dream. It seems to be the perfect hand off of color tones and luminance values between A and X tracks." I didn't know that HDRx affected color rendition, do you happen to know why? And more importantly, why and how does adding more or less HDR change the color? I love the idea of potentially adding dynamic range but the more it affects continuity the harder it will be to sell to clients.

3. "...but you can always use FLUT or ISO to boost it back up so your A-track has the original brightness you intended, and your X-track just fills in the bright details. Boosting FLUT or ISO after turning on HDRx will not add noise like you may think it would, it just re-balances the middle gray because HDRx seems to shift it by adding all the new highlight stops." Just to clarify, assuming you shot an X-track, after you turn on HDRx the ISO and FLUT sliders will use the X-track for their information instead of creating noise to brighten an image? That's an awesome little secret and might be useful on its own as a safety measure in case you are shooting a low key setup. Now you have the information you NEED (proper exposure) sitting safely on your hard drive next to the info you WANT (contrasty low key look).

Thank you again for your time and information!

 

[Hrvoje Simic]

Can the human eye notice the difference between different shots cut together with different Dynamic Ranges?

What is shot and displayed on the monitor is compressed within the same dynamic range regardless of the scene DR.
Typical LCD with 1000:1 contrast displays up to 10 stops.

Human eye is not aware of how bright the highlights and how dark the shadows were in the original scene.

For instance, if I was shooting a basic shot reverse shot scene, and one of the actors had their backs to a window, could i put on HDRx 4 to give me 20.5 stops of DR and then intercut it with the reverse shot which would be shot normally with 16.5 stops of DR?

Those numbers are more theoretical but yes.