DPX, ProRes and EX 35Mb/s comparison tests – what a nightmare!


Now I thought this would be simple. Set up my PMW-F3 with a Convergent Design Gemini and an Atamos Samurai and shoot a few shots so that I could compare the output from each recording codec. Well, the shoot side of things went just fine, a couple of different shots recording to DPX on the Gemini, ProRes on the Samurai and the internal recordings on the F3. The shots were exposed using a grey card exposed at 38%. The F3 was set to output 444 Dual Link S-Log.

However all sorts of strange things are happening when I bring the clips into my edit applications. What’s worse I get different results with different apps. For example bringing in all the material in to Adobe CS5.5 results in different luma levels for all the clips. Not only that, I also created some ProRes 4444 clips from the uncompressed DPX files and these are different again. This makes it really hard to analyse the footage when black levels are different or brightness and saturation are different. Heck all the clips were shot at exactly the same moment in time or at least within a few seconds of each other. The ONLY difference should be between the quality of the recordings. This is just more Apple Quicktime weirdness making my life difficult.

Anyway, after much head scratching and trying FCP, Avid and Premier to view the clips I was able to draw some useful conclusions which I’ll share with you here. Now the first, which may seem obvious, is that of the bunch, the Convergent Design Gemini DPX files are without doubt the best. They have zero artefacts and no added noise. After that though things become much more confusing!

Now you would expect (or at least I expected) the F3’s internal 8 bit recordings to be the worst of the bunch as all the others are 10 bit and much higher bit rates, but you know what the F3 recordings stand up really well. Why? Well in the tests I did the S-Log footage really didn’t need much of a grade to produce a nice looking image, so the clips were not being pushed very hard. One thing I’ve noticed about ProRes in the past and once again noticed in these tests, is that it’s noisy, or at least adds noise on the first encode. When you look at the Grey card in the frame grabs you can see that all of the ProRes clips show more noise than the DPX files or the F3 internal recordings, I conclude from this that ProRes is adding noise.

So in a low motion, fairly static scene the F3 recordings hold up impressively well against the ProRes ones. However I also know from experience that when you start adding in a lot of motion to a scene that 35Mb/s Mpeg can start to soften a little and in extreme circumstances really struggle and this is where ProRes starts to win as the extra data the HQ version uses really helps.

Going back to the clips from this test and looking more closely at the my wife’s face there is a difference in the way the EX codec and the ProRes codecs look. The ProRes is showing a little less blockiness and this would be a big help if you were harding the material harder. Again the clear winner is the DPX files from the Gemini, but then what do you expect!

So these are my conclusions from this test:

The Gemini DPX files produce the cleanest most gradeable images.

ProRes is noisy compared to the original source.

F3 S-Log recordings using the internal codec can be graded successfully by small amounts without obvious degradation, but I would not recommend it as you never know how much the colourist may want to push the material.

I need to shoot more challenging scenes for this type of test.

Registered users can download a 45MB zip file containing full resolution frames, graded and un-graded recorded using the Gemini, Samurai and F3. If you are not a registered user you will get the option to create an account.

[downloads_box title=”Download The Frame Grabs”]
Codec Tests Frame Grabs, 45MB

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