Editing log and HDR footage in Video by Zaweba

Many cameras and phones can record a flat, grey looking picture called log, or record HDR video in HLG or PQ. Both hold more of the scene's range than ordinary video, but neither looks right until it has been converted. Video by Zaweba handles that conversion per clip: you tell it what the footage is, and it turns it into the normal Rec.709 picture that the rest of the app works in.

Why footage needs an input colour space

A log curve squeezes a wide range of brightness into the signal so the camera can keep detail in both shadows and highlights. Played back as if it were normal video, that squeezed signal looks washed out and low in contrast. The camera maker's curve has to be undone first.

HDR formats store brightness differently again. HLG was designed for broadcast and PQ for HDR streaming and discs, and both can describe highlights far brighter than a normal screen shows. On top of that, many of these recordings use a wider range of colours, called a wide gamut, than standard video.

What you can choose

Each clip has an input colour space setting. The options cover the log curves from Sony, Panasonic, ARRI and Canon, plus HLG and PQ for HDR. Pick the one that matches how the clip was recorded, and the picture changes from flat or strange to something close to normal.

Wide gamut colour is converted to Rec.709 with filmic tone-mapping into SDR. Tone-mapping is the step that fits a wide range into a narrower one. A filmic curve rolls the brightest highlights off gently, the way film does, instead of cutting them off flat, so bright skies and lamps keep some shape. There is an exposure control alongside it, so you can choose which part of the range sits in the middle of the picture.

The honest limit

The working pipeline in Video by Zaweba is 8-bit, and there is no HDR output. HDR clips come in and are turned into standard dynamic range video for the edit and the export. For most people delivering to the web, social sites or a television that plays ordinary video, that is what is needed anyway. If you must deliver a true HDR master, that is a job for a different tool.

The 8-bit pipeline also means it pays to get the conversion right at the start. Setting the correct input colour space before you grade gives the grade the best picture to work with.

A workflow for log footage

Set the input colour space on the first clip and check it looks sensible. Then copy that setting to every other clip from the same camera. Use the exposure control in the conversion to place your subject well, and then move on to normal correction: white balance, contrast and the rest.

Some people prefer a camera maker's LUT instead. That works too through the input LUT slot, which accepts .cube or .3dl files and is applied before the grade. Use one method or the other on a clip, not both, or the curve gets undone twice.

Where log footage goes wrong

The wrong curve is the big one. Sony, Panasonic, ARRI and Canon curves are similar but not identical, and choosing the wrong maker gives a picture that is almost right, which is harder to spot than one that is obviously wrong. Check the camera's settings or the file's details if you are not sure.

Grading the flat picture is another. If you correct log footage as if it were normal video, you can get something watchable, but it takes far more effort and the colours are rarely right. Convert first.

Lastly, watch the highlights with the scopes. Tone-mapping keeps them gentle, but if the exposure control is pushed too high they still crowd up against the top of the waveform.

With the input colour space set properly, Video by Zaweba lets footage from serious cameras sit happily next to phone clips on the same timeline.