I made a mistake in this week’s webinar – Apple Final Cut Pro 11 Power Tips – when I said that ProRes did not support Log video. (I corrected this in the edited final version.)
It does.
WHAT IS LOG VIDEO
Log video is a way to record grayscale values to capture a wider dynamic range in highlights and shadows. In other words, rather than over-exposing highlights, or mushing all the dark shadows into glop, it uses logarithmic math (hence the name: “log”) to retain that detail.
However, cameras require both hardware and firmware to support this feature. You can’t convert non-log video to log in post-production. The video needs to be recorded that way. As well, all log video requires color grading. If you are in a hurry, log video is a bad choice.
Here’s an easy way to visualize why log is so helpful. Normally, Rec. 709 records video where the grayscale difference between each IRE value is the same. (This is the straight green line.)
While this creates perfectly fine images, it also means that any grayscale values that are too bright are recorded as over-exposed. And, once over-exposed, nothing can be done to restore the original detail. In this chart, we are only able to record grayscale values from 0 – 100.
What log video does is scale recording values so the differences between IRE values are small in the shadows, but large in the highlights. This allows us to record much brighter highlights without over-exposure. Again, in this chart, we can record grayscale values from 0 – 450!
Click to see larger image.
As you might expect, there’s no free lunch. Log images are very gray.
Though we have captured all these values, the limited grayscale range of Rec. 709 – which we must honor when creating our final program – means that, during color gradine, we need to select which parts of the image we want to show. Maybe we emphasize shadows, or mid-tones, or highlights. The choice is ours, but we can’t show everything, the specs don’t allow it.
NOTE: This is exactly the reason that HDR was invented. HDR allows a MUCH greater range in grayscale values. With HDR, shooting log means we can capture more highlights and show them on the screen.
Since log footage needs to be recorded by the camera, most log footage is not ProRes. Popular log formats include:
Additionally most cameras record log video using codecs other than ProRes. For example, Panasonic records V-log using AVC1.
PRORES 422
The reason all this matters is that, using Final Cut Pro, optimizing or rendering your media means you are converting it from its source format into ProRes 422. If ProRes did not support log format video, you’d be stuck.
But it does.
Let me illustrate using video shot on a Panasonic EVA-1, using Panasonic V-log.
An ungraded, Panasonic V-log image. Click to see larger picture.
Here is the original image (left) in its ungraded, log state. On the right is the same image rendered into ProRes 422.
NOTE: Panasonic records using the AVC1 codec. This can be edited natively in Final Cut, without requiring optimizing media. But, rendering transcodes this into ProRes 422. If you want to edit camera native, don’t optimize your media.
Click to see larger image.
All log formats require applying a camera LUT before color grading to convert the video into the correct color space for your project. Here’s the same frame with the Panasonic V-log LUT applied, but no other color grading.
Click to see larger image.
Here’s the same frame fully color graded. In all cases, the ProRes 422 version looks the same as the camera native version.
SUMMARY
As we can see from these examples, ProRes 422 fully supports log video. Which means you won’t lose anything if you need to transcode from the log format the camera shot into ProRes.
However, all log footage will need a camera LUT applied to convert it into the Rec. 709 color space, then a polishing color grade to make it look the way you want.
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2 Responses to Yes, ProRes Supports LOG Video
Sending RED RAW (R3D) to VFX house is it better for them to return in log or with LUT conversion?
If you converted Log file to ProRes without a LUT, what LUT would then be applied as a starting point?
I assume ProRes log would require a full grade without a LUT
Brad:
1. Log vs. LUT. This depends upon what you want to do with the non-VFX footage and where color grading will occur. In general, you would want the VFX house to return footage in a format that matches the rest of your project. That way, you grade them all the same. This answer depends upon who’s doing the grading, what’s involved in integrating the VFX footage with that which is shot in camera, your level of expertise, the project itself and so on. Chat with your colorist and VFX folks and see what they recommend.
2. If the ProRes copy matches camera native, ie both are log, then apply the same camera LUT to ProRes as you would apply to the camera native media.
3. Log files – with or without a LUT – need a color grade. LUTs get you close, but they never get you fully there.
Larry