DSLR Raw Photos Explained

Many good-quality DSLR cameras I’ve seen will have the ability to save your photos in a few different formats, JPEG, TIFF, or some form of raw format.

If you’ve every tried to use one, you’ll quickly realize they’re not like normal photos and don’t quite work the same. So what exactly is this, and what is it used for?

A raw file is also known as a ‘digital negative’, and that’s actually a rather good comparison. It stores the unmodified, unprocessed, raw sensor output, in a format that’s capable of being tweaked and changed slightly.1 And like a physical film negative, you need to process and prepare them before you can use it as an actual photo.

Since it’s just the output, there’s a lot more values that can be played with unlike a traditional photo file:

  • Demosaicing method (we’ll discuss this later)
  • Defective pixel removal (We’ll cover this and a little more in another post)
  • Better white balance tweaking
  • Noise reduction
  • and more

You can essentially tweak one and “re-expose” the image, using just some appropriate software.

Raw files are usually not compressed at all, or compressed with a lossless format, meaning that you don’t lose any quality for using them, and in most cases, will be one of the highest quality formats you can save shots… and also the biggest, meaning you’ll have less pictures per storage device, be it is SD card, CompactFlash, what have you.

If you have the few minutes it takes, saving to raw, grabbing one of many free programs for processing (RawTherapee is my choice, though I head DarkTable can be pretty good too), and exporting from that, is going to be a good way to get the highest quality possible. Then again, what you do is up to you. I’m just providing information.

Now, Demosaicing

Fun fact: a CCD or CMOS image sensor is actually, in a way, black and white only. It can’t sense color, it just counts photons, which by themselves have no “color” when you’re just counting them. To overcome this limitation, all (digital) cameras will contain a filter that gives each sensor pixels a color, one of the most common and longest-running designs is the Bayer filter.

The Bayer filter colors 50% of the sensor pixels green, 25% red, and 25% blue. Now, if you’ve ever zoomed into any picture, this isn’t what they look like. A program has taken this pattern of colors and reconstructed the ‘actual’ (or best approximation) colors that were present in the scene. This process is called demosaicing.

There’s many different methods that can be used to demosaic a photo, and each has its strengths and weaknesses. Some are better for producing less noise, some are better in lower light, some work better on different color filters.

So if you’re obsessed enough, or have a high enough quality standard that you want to change every single processing step, replace whatever the camera usually does with whatever you direct, then raw files are probably your best bet. Unless you’re a professional photographer or just someone who likes to tinker around, it’s not a requirement, it’s just fun trivia.

  1. Not 100% true, there’s some processing done to the file, and I’m not talking about the packing and encoding to put it into whatever, well file the camera exports. You will never have a literal raw output from the sensor, but it’s as minimal as you can realistically get. ↩︎