I'm writing my bachelorthesis to finish my studies here in germany. My topic is "production of professional videomaterial to compare different cameras".
I read an article by Art Adams over at provideocoalition about the differences between Raw and Log Files.
I've got a few questions going a bit deeper into the topic though:
Art wrote the following in his article:
16,384: totally saturated sensor (maximum white)
8,192-16,383: First stop down from maximum white
4,096-8,191: Second stop down from maximum white
2,048-4,095: Third stop down from maximum white
1,024-2,047: Fourth stop down from maximum white
512-1,023: Fifth stop down from maximum white
256-511: Sixth stop down from maximum white
128-255: Seventh stop down from maximum white
64-127: Eighth stop down from maximum white
32-63: Ninth stop down from maximum white
16-31: Tenth stop down from maximum white
8-15: Eleventh stop down from maximum white
4-7: Twelfth stop down from maximum white
2-6: Thirteenth stop down from maximum white
1-2: Fourteenth stop down from maximum white
So he's talking about the digital values and the brightness stops they represent using Raw files.
Then in log mode the data is compressed using logarithmic scales.
This is how I imagine it's working:
For every pixel in the image data using Raw is stored like this:
Red: 10111011100000 (representing 12000 in binary values)
Blue: 10011100010000 (representing 10000 in binary values)
Green: 1111101000000 (representing 8000 in binary values)
I dont exactly know what color this would be but just to have some example values.
So in Raw the file is getting quite big because those values
for every pixel is quite much data (at least in 4:4:4 for every pixel).
First question: is this roughly how data is stored (there will be some more meta data in the file, but i guess this is how pixel color data is stored?)
Second question: how are those values compressed in log?
Everyone is always talking about brightness being compressed in log, but i guess what is actually meant are the brightness values for each color channel seperately (as I did in my example above).
Since in log the data has to be stored in binary values too, how are the log values written exactly?
Hope someone is able to help me. I may be asking some more in-detail questions in this thread over the next few weeks while im writing.
Thanks in advance.