Videographers transitioning between shooting in Log and RAW video may find it’s not always smooth, especially when it comes to color grading.
According to Syrp Lab, the difference between Log and Raw shooting has to do with the approach, and to better understand these approaches, it’s important to understand how a camera records image data.
When light passes through the lens and lands on the camera’s image sensor, the light is converted into an electrical charge. The brighter the light, the greater the electrical charge. This charge is then transferred to the processor which transforms it into digital data, which is then saved and written to storage.
But there is a problem: the electrical signal is “analog” so that as electricity flows from high to low, the signal strength value increases and a processor must assign a specific value and break it down into steps. It can be likened to descending a slide or descending a staircase: both descend, but very differently.
The value assigned to each pixel at that exact moment is then rounded up or down by the camera, which is the bit depth. Syrp describes an 8-bit file as having 256 possible values while a 12-bit file will have over 4000 possible values. Therefore, the higher the bit depth, the more information and the larger the file.
When recording a video in RAW format, the bit depth will retain all possible data values and these values will be available. During color grading, the image remains smooth due to all the data values it has. It’s a bit like a slide: smooth and consistent.
In Log there is some data latitude to assess, especially at higher bitrates, however, there is a point where the picture starts to break. So it’s best to make gradual and not extreme changes due to Log removing some of the repeatable values from an image to reduce file size.
“Once you get into the rating and realize that this shot might be a little different, you start stretching your values along that curve, and things…break,” says Film Science’s Chase Madsen. “Think of it again as that staircase. When you need to change the shape of the stairs, some stairs become too tall to climb.
Even a 12 bit image is mapped to an 8 bit curve. Therefore, when changes are made, this data is not available to be adjusted and hence image banding occurs. Add file compression, noise reduction, and image sharpening, and banding can become very noticeable and the image becomes unusable.
This is where saving images in RAW format is useful for color grading. It retains all available image data values for that bit rate and therefore provides much greater latitude. But when using Log, the note can’t do much before it starts breaking.
Shooting at the highest possible bit rate will preserve more color values and data. Even shooting 10-bit over 8-bit will provide four times the data. Videographers should therefore shoot at the highest possible bit rate if they plan to grade the footage.
If Log is the only option, or the preferred one in order to reduce storage requirements, videographers need to ensure that they are properly lighting a scene and using the highest possible bitrate to give themselves the most leeway in post. RAW will however be the better bet, even if it means it requires much more storage capacity in the camera and in the editing bay.
More examples and a larger description of the principles explained above can be found on the Syrp Lab website.
Picture credits: Photos by Syrp Lab