… for Codecs & Media

Tip #1043: Comparing HDR Grayscale to SDR

Larry Jordan – LarryJordan.com

HDR HLG matches SDR shadows and midtones, but adds more highlights.

As I was researching my recent webinar on “New Features in Adobe Premiere Pro,” I came across an interesting graph that compares HDR HLG grayscale values with SDR.

We are all familiar with the grayscale values in SDR (Standard Dynamic Range) media. It’s the Rec. 709 HD footage we work with on a daily basis.

While HDR consists of more than simply brighter pixels, grayscale is the relevant concept here. HDR has two formats: HLG and PQ. HLG (Hybrid Log Gamma) is optimized for broadcast, while PQ is optimized for digital display. Both Final Cut and Premiere support HLG media. But, what does it mean to say “optimized for broadcast?” That’s where this chart comes in.

SDR grayscale values are essentially linear, a “straight line” from 0 IRE (pure black) to 100 IRE (pure white). This range of 100 IRE values is what the entire broadcast signal path is designed to support.

HDR HLG mirrors the linear SDR grayscale values from 0 to 75 IRE – though there is some variation between standards in different countries – then expresses highlights as log values, rather than linear for the top 25% of highlights.

This allows HDR HLG to pack much brighter highlights than SDR, yet still fit within a 100 IRE range. However, there’s a trade-off. While HDR HLG is compatible with broadcast, HDR PQ has more highlight detail. Both HDR formats are much brighter than SDR.

EXTRA CREDIT

If you are creating an HDR project, it is important to know what format your distributor supports BEFORE you do the color grade, because grading HLG and PQ is not the same and you can not switch between them.

… for Codecs & Media

Tip #1049: HDR HLG vs PQ on SDR Monitors

Larry Jordan – LarryJordan.com

HLG looks better on SDR than PQ. But PQ looks better on HDR monitors.

Tip #1043 compared the grayscale differences between HDR HLG and SDR. This tip illustrates the differences between watching HLG and PQ on an SDR monitor.

NOTE: The screen shot and the information in this article are taken from a Venera Technologies article.

To display the digital images on the screen, display devices need to convert the pixel values to corresponding light values. This process is usually non-linear and is called EOTF (Electro-Optical Transfer Function).

While SDR uses Rec. 709, HDR defines two additional transfer functions to handle this issue – Perceptual Quantizer (PQ) and Hybrid Log-Gamma (HLG). HDR PQ is an absolute, display-referred signal while HDR HLG is a relative, scene-referred signal. This means that HLG-enabled display devices automatically adapts the light levels based on the content and their own display capabilities while PQ enabled display devices need to implement tone mapping to adapt the light levels.

Under ideal conditions, dynamic PQ based transformation will achieve the best quality results at the cost of compatibility with existing display systems.

As you can see from the screen shot, HLG images look better on SDR monitors than PQ images. However, while PQ based transforms promise to display the best quality results on HDR enabled monitors, in comparison to HLG, PQ requires proper tone mapping by the display device.

EXTRA CREDIT

As you may be able to see in the screenshot, PQ offers more detail in the highlights than HLG.

… for Codecs & Media

Tip #1013: The Coming File Size Tsunami

Larry Jordan – LarryJordan.com

The impact of increasing frame size AND frame rate requires exponential growth in storage.

Last week, I presented a webinar on media management that applied to both Premiere and Final Cut. During the presentation I was discussing the impact frame size, frame rates and bit depth have on the file size of our media files.

The world of 8K images is coming – whether we like it or not; though, personally, I’m not looking forward to it. But, the impact of 8K on our storage capacity and bandwidth is dramatic!

As I was presenting, I realized I was missing a chart that showed the result of both frame size AND frame rate increasing. So, here it is. As this chart shows, as both frame size and frame rate increase, we see an exponential growth in file size and bandwidth.

• 720p24 uses 23 GB/hour
• 1920p30 uses 66 GB/hour
• UHD/30 uses 530 GB/hour
• 8K/60 uses 2,263 GB/hour

This means that as you plan future projects make sure your storage system has the capacity to handle it!

… for Codecs & Media

Tip #991: HDV vs. “Normal” Media

Larry Jordan – LarryJordan.com

Make sure your projects match the aspect ratio of the pixels, as well as project.

The big difference between HDV and “normal” media is the aspect ratio of each pixel. Just today, I got an email from a reader asking why their footage looked “stretched.” Here’s what you need to know.

Back in the old days, as we were making the transition from standard definition video to HD, cameras and storage devices were neither big enough nor fast enough to capture and record a full HD video stream.

To solve this problem, Sony and Panasonic created HD formats with non-square pixels. This meant that they could record fewer pixels, then stretch them horizontally in the final display so that fewer pixels would fill more space.

For example, while HDV records 720p footage using square pixels, instead of recording an image at 1920 x 1080, it records it using 1440 x 1080, then stretches each pixel’s width to fill the space of 1920 pixels, using only 1440 of them.

The problem this causes in editing is that, today, NLEs expect HD pixels to be square. When you work with older footage, if your image looks squished, check your pixel aspect ratio – or your project settings – to make sure you are compensating for these earlier rectangular pixels.

EXTRA CREDIT

Here’s a link from a few years ago that looks at HDV in more detail.

… for Codecs & Media

Tip #996: More Proxy Options in Compressor

Larry Jordan – LarryJordan.com

Proxy workflows are very helpful for multicam edits, as well as frame sizes greater than 4K.

With the 4.4.7 update to Apple Compressor, Apple added more proxy options as compression settings. In the past, we could only convert proxies to ProRes Proxy. Now, however, we can create proxies using either ProRes or H.264.

NOTE: Well, that statement isn’t completely true. You could create custom compression settings for just about any format, but this update makes proxy creation a lot easier by pre-building more compression presets.

A new “Proxy” category was added to Compressor. Inside you can choose between ProRes Proxy and H.264. H.264 files will be smaller, but ProRes will be more efficient to edit (meaning they will render and export faster).

NOTE: Using HEVC for editing proxies is not recommended because the complexity of the compression format makes them tend to bog down the system.

In addition to the two codecs, you can also choose the frame size of the proxy as a percentage of the frame size of the master file. Reducing the frame size shrinks file sizes still smaller, but also decreases image quality. To minimize storage requirements, pick the smallest proxy file that still shows enough detail to make informed editing decisions. If space isn’t an issue, use one-half size; that always yields the highest image quality.

I did a quick test. Starting with a 1 GB ProRes 422 master, a half-size ProRes Proxy file was about 90% smaller than the original. In comparison, H.264 was about 10% the size of each ProRes Proxy file. As well, each reduction in frame size cut file size by roughly 2/3.

If file storage is not a big issue or if you are editing on an older system, choose ProRes Proxy. This is a highly-efficient codec, optimized for editing, that runs well on slower systems. It also provides a slightly higher image quality, compared to H.264.

If conserving file storage is important, you need to share project files with another editor, or you have a newer system, H.264 may be the better choice.

Most of the time, we just need to see proxy files to make basic editorial decisions. When the time comes for adding effects and color grading, its a single click in the NLE to switch back to full-quality masters. As with all projects, run tests to see what works best for you before starting a major project. On the other hand, you can always regenerate proxy files and relink them, if you change your mind.

EXTRA CREDIT

You can use Compressor to create proxy files for any NLE. Final Cut also replicates these same proxy formats, so you can use the built-in proxy creation process in FCP X, if you prefer.