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By now you should have a general understanding of what a raw file is. In this part I will try to explain how raw files are typically used in some camera systems.
Each camera system samples an image and creates a raw file in a unique way – sort of how a chef writes a recipe or a doctor writes a prescription. Even if the person reading it – maybe a pharmacologist or sous chef – is a highly trained professional, he/she still needs to deal with the idiosyncrasies of the person writing the recipe or prescription. Interpretation is everything.
Information from a sensor can be interpreted in infinite ways, and no program or hardware can be perfect. At best, a raw file is a set of instructions on how the sensor interpreted light that fell on it under certain conditions. In an ideal world, we’d have perfect raster images, uncompressed, coming out of sensors with well defined color spaces – that day isn’t here yet. So the onus lies on us to use whatever software is available to create our own raster images the way we see fit.
Keeping this in mind, let’s take a brief look at how some manufacturers deal with raw files. For the sake of simplicity, I’m avoiding metadata – but they do impact the size of a file by about 5% to 10%, or even more if it’s a quirky system.
DSLR RAW – CR2 and NEF
The two giants of the still camera industry – Nikon and Canon – both have proprietary raw files – NEF and CR2. A lot of information about these files is hidden from the general public, for reasons nobody need care about.
Typically, the file size of a NEF or CR2 file is one-third the size of an uncompressed file of the same resolution. If you take a photo with either camera and then convert them into a TIFF file in a raw converter – you should be able to learn quite a bit about the system.
Nikon D800 NEF 7360×4912 14-bit
Uncompressed size, without metadata, should be = 181 MB
Canon 5D Mark III CR2 5760 x 3840 14-bit
Uncompressed size, without metadata, should be = 110.74 MB
LEICA M9 – DNG
DNG 5212×3472 14-bit
ARRI ALEXA – ARRIRAW
Arriraw 2880 x 1620 12-bit Log
Data Rate @ 24 fps = 168 MB/s
RED EPIC – REDCODE RAW
Redcode Raw 5120 x 2700 (Full Frame 1.90:1) 12-bit (and 16-bit, as claimed by Red)
Redcode compression = 3:1
So, is Redcode really 16-bit? You decide.
BLACKMAGIC CINEMA CAMERA – CINEMA DNG
CinemaDNG 2432 x 1366 12-bit
Maximum Data rate @ 30 fps = 150 MB/s
This article should have clearly shown why the word ‘raw’ should not be used as if it meant just one thing. Its properties, size and quality can vary as any other file type – either by commission or omission on the part of the camera manufacturer.
One universal feature of raw files are that they are smaller in size than full raster files – but this is because they don’t have full color information. Furthermore, due to the nature of bayer sensors, one isn’t getting the full resolution of the sensor, too.
The challenge for those working in raw, then, is that they have find algorithms that will take this one-third quality sensor data and interpolate it to the best quality raster RGB file possible for delivery.
If this can be done to the subjective satisfaction of the end user, then raw files are indeed an excellent option to get great quality at approximately a third of the data rate of uncompressed media. In the next and last part I’ll look at a few software options for raw conversion.