Videographers who transition between shooting in Log and RAW video might find that it isn’t always smooth, especially when it comes to color grading.
According to Syrp Lab, the difference between shooting in Log versus Raw has to do with approach, and to better understand these approaches, it’s important to understand how a camera saves image data.
As light hits the sensor of the camera, it is transformed into an electric charge. Electrical charges are greater for brighter light. This charge is then transferred to the processor which processes it into digital data, which is then saved and written to storage.
But there’s a problem: The electrical signal is “analog” so as the electricity flows up and down, so goes the value of the signal strength and a processor has to assign a specific value and break it down into steps. It can be thought of akin to going down a slide or descending a flight of stairs: both go down, but very differently. The value that is assigned to each individual pixel at a given moment is then rounded up by the camera. This is called bit depth. Syrp describes an 8-bit file as having 256 possible values while a 12-bit file will have over 4,000 possible values. The file will be larger if it has more data.
When saving video to RAW, all data values are preserved and will remain available. During color grading, the image remains smooth because of all the data values it has available to it. This is much like a slide: smooth and consistent.
In Log, there is a certain amount of data latitude to grade with, especially in higher bit rates, however, there is a point where the image begins to break. Log will remove some repeatable images from an image to reduce the file size. It is best to change slowly and not make drastic changes.
“Once you get into the grade and you realize, hey this shot could do with being a little different, you start to stretch your values along that curve, and things… break,” says Chase Madsen of Film Science. “Think of it as that staircase again. When you need to change the shape of the staircase, some of the stairs become too big to climb up.”
Even a 12-bit image is mapped to an 8-bit curve. Image banding is caused by changes to the data. The image can be rendered unusable if it is not compressed, reduced in noise, or sharpened.
This is where saving images in RAW comes in handy for color grading. This allows for greater flexibility and keeps all available data at that bit rate. But when using Log, the grade can only do so much before it begins to break.
Using the highest possible bitrate will save more data and color values. Even shooting in 10-bit over 8-bit will provide four times the amount data, so videographers should shoot in the highest bit rate they can if they plan to color grade the footage.
If Log is not an option or the best choice, then videographers should ensure that they properly light a scene, and use the highest bitrate possible to allow for as much post-production flexibility. RAW will be your best option, though it may require more storage space in both the camera and the edit bay.
More information and examples of these principles can be found on Syrp Lab’s website ..
Image credits: Photos by Syrp Lab