Jump to content
Evan Richards

How are movies that end up on 4k blurays being converted to HDR?

Recommended Posts

I'm not sure I understand what's going on with 4k blurays. So, these films are somehow scanned at 4k resolution in High Dynamic Range using Rec 2020 colorspace? How is this accomplished? I've mainly worked in VFX, and I know that the films I've done VFX for did not have effects shots that were high dynamic range. A lot of matte paintings, sky replacements, etc were decidedly low dynamic range.

I can understand if all the the negatives were re-scanned then you could capture something that might be higher dynamic range than you had baked into the digital version found on a standard bluray, but how can SDR footage be converted to HDR?

I'm asking out of curiosity because I've been trying to get 4k stills out of movies as reference images, but they all end up looking very different from the regular HD/bluray. I don't know much about the conversion process, but it SEEMS like you should be able to take 10bit HDR footage and make it look like the 8bit SDR HD footage. Any thoughts?

Share this post


Link to post
Share on other sites

HDR Film scanning is generally a 2 pass process. The first pass is the entire image as it sits. The second pass is generally the black's only, then the image is combined. They call it HDR because it does have more dynamic range, specifically in the blacks, than a normal scan does. I usually work with these scans in raw data mode (DCI-P3 color space) in Resolve. Getting a rec 2020 output for UHD BluRay is  easy from there and it works very nicely. The reason why film isn't naturally HDR is because of the printing and projecting process, it naturally compresses the dynamic range quite a bit unfortunately. However, there is more data on the film than most people think there is. 

Is it real HDR? I guess? I mean it for sure looks better than a normal scan in the blacks. The amount of detail that can be pulled from the film stock is amazing, no more muddy blacks. I can't even show you how good it looks on a computer because there is no web playback program capable of delivering the black levels correctly. On my grading monitor it's night and day. 

Digital SDR footage can't be converted to HDR unless they went back to the original source files and re-colored the entire movie. 

I don't know how one would grab stills from a UHD BluRay source. Also, very few UHD BluRay's are HDR, most of them are SDR made from 2k sources. The studio's have put in little effort to re-scan their movies in 4k for UHD releases. Most of them took archival 2k scans and up scaled them to UHD for the releases, which really sucks. I think Warner Brothers is the only studio pushing for real UHD finishes for their releases. Heck the main benefit UHD BluRay is the 10 bit 444 codec, which until UHD BluRay was released, was impossible achieve at the home video level. 
 

Share this post


Link to post
Share on other sites

Visual effects are usually delivered in log gamma (or on older titles, laser recorded onto film internegative, so they have the same gamma as the rest of the negative) so unless Rec.709 / P3 was baked into the only masters, then going back to a log gamma master should provide enough dynamic range for an HDR version.  

I can't imagine a major movie shot raw / log -- or on film scanned to log -- is cutting in display gamma (Rec.709) vfx shots into their log master. Certainly when I'm color-correcting my current show for Amazon, I can see that the vfx shots are delivered in log gamma. But I'm not denying that some shows might be delivering vfx in Rec.709, but usually that would be for a TV show.

Share this post


Link to post
Share on other sites
Posted (edited)
On 4/18/2020 at 3:28 PM, Tyler Purcell said:

I don't know how one would grab stills from a UHD BluRay source. Also, very few UHD BluRay's are HDR, most of them are SDR made from 2k sources.

Hmmm. That's interesting. I haven't found that on the blurays I've examined, but I guess I haven't looked at bery many. The ones I examined were "The Post", "Atomic Blonde", and "Moonlight".  If what you say is true, that most are SDR made from 2k sources, it seems like you'd be able to apply a rec 2020 to rec 709 LUT to make the 4k bluray footage match the HD footage? But I haven't found that to be the case. Check out these 4 images from Atomic Blonde (slight nudity warning). https://imgur.com/a/1jZD3jm

The First image is taken from the bluray, the second image is taken from the UHD bluray and had the color tweaked as it was being extracted. They don't look too similar. The UHD images look much more colorful, contrasty, and overall brighter. It seems like the way the UHD looks would have the original intention for how it should look, but both of these images are backed down to JPGs which means they COULD have gotten this look in the HD bluray, but chose not to. So...maybe the was the HD bluray looks IS more or less how the film was expected to look?

Edited by Evan Richards
Clarification

Share this post


Link to post
Share on other sites
On 4/18/2020 at 3:37 PM, David Mullen ASC said:

Visual effects are usually delivered in log gamma.

Yes. I suppose that's true. I had forgotten that as we always have the show LUTs built into Nuke and RV that automatically convert our images to the proper viewing space without us having to do anything.

Share this post


Link to post
Share on other sites
On 4/18/2020 at 3:40 PM, David Mullen ASC said:

You might find this interesting, it's about putting HDR frames up for a blu ray review website when they know people are not watching on HDR monitors.

http://www.dvdbeaver.com/film/DVDCompare3/saving_private_ryan_UHD_blu-ray.htm

Thank you, this is very useful as this is exactly what I am trying to do. To my eye though, the color of the "simulated" images seems far enough away from the original Bluray that it make me wonder which image more closely represents the DP's vision. I mean, people have been watching blurays on standard HD TVs for years, but does the fact that the UHD blurays look so different mean that standard blurays never truly represented what the DP wanted you to see?

Share this post


Link to post
Share on other sites

Considering the DP's often color-corrected the home video master, and since D.I.'s the same correction for theaters was used for home video once trimmed for Rec.709, I think the standard blu-rays represented what the DP wanted you to see IF they supervised it.

Keep in mind that if you do a D.I. for theatrical release in a DCP,  it's in P3 color space / gamma which is not far removed from Rec.709 display gamma for monitors.  It's only for some special IMAX and Dolby Cinema presentations using laser projectors that you can even make an HDR version for cinema.

It could be argued for older titles, it's the HDR version that looks different than the movie ever looked in the past.  A contact print projected may have had the black levels closer to an HDR release but it never had the image brightness of HDR because projection was standardized to 16 foot-lamberts and was usually a bit lower.  And HDR is capable of displaying all 14 to 15 stops of information on the film negative, which a film print or a P3/Rec.709 version didn't if they wanted decent contrast.

I wouldn't think of HDR vs. SDR in terms of which is more "accurate" but just as another way of looking at images.

Share this post


Link to post
Share on other sites
Posted (edited)
7 minutes ago, David Mullen ASC said:

Considering the DP's often color-corrected the home video master, and since D.I.'s the same correction for theaters was used for home video once trimmed for Rec.709, I think the standard blu-rays represented what the DP wanted you to see IF they supervised it.

Keep in mind that if you do a D.I. for theatrical release in a DCP,  it's in P3 color space / gamma which is not far removed from Rec.709 display gamma for monitors.  It's only for some special IMAX and Dolby Cinema presentations using laser projectors that you can even make an HDR version for cinema.

It could be argued for older titles, it's the HDR version that looks different than the movie ever looked in the past.  A contact print projected may have had the black levels closer to an HDR release but it never had the image brightness of HDR because projection was standardized to 16 foot-lamberts and was usually a bit lower.  And HDR is capable of displaying all 14 to 15 stops of information on the film negative, which a film print or a P3/Rec.709 version didn't if they wanted decent contrast.

I wouldn't think of HDR vs. SDR in terms of which is more "accurate" but just as another way of looking at images.

Thank you David. This clarifies a lot of my questions.

Edited by Evan Richards

Share this post


Link to post
Share on other sites
2 hours ago, Evan Richards said:

That's interesting. I haven't found that on the blurays I've examined, but I guess I haven't looked at bery many. The ones I examined were "The Post", "Atomic Blonde", and "Moonlight".

Well, that's because those are all 2k movies. The Post was shot on 35mm, but there was no negative cut made, so the 2k DI is the "master". Both Atomic Blonde and Moonlight were both shot on sub 4k cameras and finished in 2k. So no, you can't really compare those UHD releases to actual UHD releases. Ya gotta go out and buy an "actual" UHD release, which is why I recommended Dunkirk. Another good modern title would be Once Upon a Time in Hollywood. Both films are shot on film, both were over-scanned (5k - 11k) and then finished in 4k. You can't get a better example of what UHD BluRay is suppose to look like, than those two films in my opinion. 
 

3 hours ago, Evan Richards said:

If what you say is true, that most are SDR made from 2k sources, it seems like you'd be able to apply a rec 2020 to rec 709 LUT to make the 4k bluray footage match the HD footage?

Ok so maybe this is the disconnect. The way UHD BluRay works, is the display device will tell the player if it can work with HDR material and if it can, the player will spit out the Rec 2020 version. Otherwise, if there is no Rec 2020 device connected, it will actually create a 709 version on the fly. 

You can turn Rec 2020 into Rec 709. You can't turn Rec 709 into Rec 2020. Once you've compressed the image, you can't get the missing information back. 

2 hours ago, David Mullen ASC said:

I wouldn't think of HDR vs. SDR in terms of which is more "accurate" but just as another way of looking at images.

I agree... when you watch films restored on HDR UHD BluRay, they don't look like the film. I have a few releases done like that and it's quite astounding how much they can pull from the film, but it doesn't reflect what the movie was originally looked like. 

Share this post


Link to post
Share on other sites
1 hour ago, Tyler Purcell said:

You can turn Rec 2020 into Rec 709. You can't turn Rec 709 into Rec 2020. Once you've compressed the image, you can't get the missing information back.

But if the UHD version has an extra layer of blacks for more contrast, then I guess it wouldn't be as simple as a LUT. You'd have to do some tone mapping I guess (for going from Rec 2020 to Rec 709)?

Share this post


Link to post
Share on other sites
On 4/20/2020 at 1:55 PM, Evan Richards said:

But if the UHD version has an extra layer of blacks for more contrast, then I guess it wouldn't be as simple as a LUT. You'd have to do some tone mapping I guess (for going from Rec 2020 to Rec 709)?

It's not that simple sadly. Rec 2020 to Rec 709 is a completely new grade. I do it all the time and it's not a LUT fix. You have to literally re-grade 

Share this post


Link to post
Share on other sites

Join the conversation

You can post now and register later. If you have an account, sign in now to post with your account.

Guest
Reply to this topic...

×   Pasted as rich text.   Paste as plain text instead

  Only 75 emoji are allowed.

×   Your link has been automatically embedded.   Display as a link instead

×   Your previous content has been restored.   Clear editor

×   You cannot paste images directly. Upload or insert images from URL.



  • Glidecam



    CineLab



    Visual Products



    Ritter Battery



    Tai Audio



    Gamma Ray Digital Inc



    Serious Gear



    FJS International



    Metropolis Post



    Rig Wheels Passport



    New Pro Video - New and Used Equipment



    G-Force Grips



    Broadcast Solutions Inc



    Paralinx LLC



    Abel Cine



    Media Blackout - Custom Cables and AKS



    The Original Slider



    Wooden Camera



    Just Cinema Gear


    Cinematography Books and Gear
×
×
  • Create New...