601/709 to RGB Filter

A common problem taking a video from Avid to Final Cut is color space- Avid works in 601/709, and Final Cut works in RGB. This leads to low contrast video when using a video exported with Avid in FCP. Luckily, Avid can export as RGB as well.

Take for instance, this still from a video of quaking aspens shot with an iPhone. The one on the top was exported from Avid as 601/709, and the one on the bottom was exported as RGB.

The difference is slight, but the darks aren’t as dark, and the lights aren’t are light in the one exported as 601/709. Putting the 601/709 version on top of the RGB version in the FCP timeline and changing composite mode to difference on the 601/709 version shows where there are differences. It’s hard to see (try staring at it for several seconds, or adjusting your viewing angle of the screen), but the waveform shows there is up to 10% difference in the colors.

A quick overview of the difference between RGB and 601/709- a digital color is made up of a Red, Green, and Blue value. Each can have a value of 0 to 255.

In 601/709, black has a value of 16,16,16, and white has a value of 235,235,235. Here’s the waveform for the aspens shot which was exported in 601/709-

In RGB, black has a value of 0,0,0, and white has a value of 255,255,255. Here’s the waveform of the aspens shot, exported as RGB-

Notice the differences between the two waveforms- the RGB one stretches further into black, and further into white (to the point of clipping – thanks, iPhone).

Both color spaces their perks- 601/709 can handle values blacker than black, and whiter than white, but RGB has more information (256 steps between white and black, versus 220 for 601/709).

To handle this difference, I wrote a filter, that basically takes each value from a 601/709 file, and “stretches” it out to RGB space.

Here’s what the filter does with the aspen shot- the top is the original exported as 601/709, the middle is exported as 601/709, with the filter, and the bottom is the original exported as RGB.

The filter has brought the 601/709 footage much closer to the RGB, how it should be in Final Cut. How close? Using the same difference composite mode technique, I can see it’s much closer, in fact within 3%.

As you can see, it will not match exactly, but it will work in a pinch. If you can reexport the file as RGB, that is preferable, but there are many instances (lost master, time constraints) where that isn’t possible.

Download the filter by right clicking and saving- 601-709RGB.fcfcc.

To install, unzip the file, and place the filter into /Library/Application Support/Final Cut Pro System Support/Plugins/ and relaunch Final Cut Pro. It will be in the Image Control folder in the Video Filters section. Apply it to a 601/709 clip, and it should be fine. If it’s a bit off, try messing with the “Adjust” Parameter until it’s correct.

Let me know how the filter works for you!

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2 comments on “601/709 to RGB Filter
  1. Sergio García says:

    Thanks James!

    But is there any possibility to keep 601 with final cut in order not to lose quality?

    Best regards,

    S.

  2. James says:

    Sadly, no. The only way would be to export from Avid as 601/709.

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