What is a raw file and why should it not be called RAW?


People who don't use raw files are sometimes confused as to what they're all about so I decided to write this little help sheet. 

First bits

When you take a photo with your camera you are allowing light coming through the lens to pass through the shutter and fall onto the sensor. The sensor detects the light colours and strength as information, or data, records it into memory, then converts or processes it into a picture file, almost always a JPG, (some use JPEG) and compresses it, like you would Zip a Word document.

Sometimes you can set your camera to do certain things when it converts the data into a picture file. You can tell it to drop all the colours and have only Black and White, you can tell it to add a filter to make the picture sepia, or you can add simple things like a little extra brightness, more contrast, and even a little sharpness. This all happens when you take the picture and you don't see anything going on, you simply see the preview screen show you the shot you just took. 

Most cameras allow you to save to JPG Small, Medium and Large, or Fine. JPGs are compressed data as said and some of the data can be dropped without most noticing any difference. This saves on space mostly but as space in computers is relatively cheap now, there's little point in choosing any other than the best quality option. That is, the largest file. 

You then transfer the JPGs to your computer and edit them in photo editing software (list of programs available coming soon)...or not! Most people edit to a small degree, even if that's fixing the horizon cos it's wonky, adjusting the exposure cos it was too dark/bright, or enhancing the colours by saturating them slightly. 

Some cameras allow you to save in TIFF or DNG format, we'll not worry too much about them here. 

Next bits

Most cameras nowadays have a setting also called raw. Unlike TIFF, JPG and DNG, raw doesn't stand for anything. That data that your sensor collects, it's just unprocessed, or raw data, it's RGB values for each sensor pixel. That's why it's called raw. Most cameras allow you to save a raw file and a JPG at the same time. This is simply so you have a JPG file you can look at quickly once it's on your computer. When you've decided which ones you're going to keep, you can delete all the JPG's if you like. 

To do anything with this raw data you need some software and everyone uses the software that they prefer. My preference is Lightroom, but there are many out there, some are even freeware, free to download and use from the internet.

When you open the raw file in whatever software you use, it does what's called de-mosaicing. This is a term which simply means the software reads the data, and presents it in a form that you can see on screen. You may notice that at first the picture isn't as pretty as a JPG, but that's because the camera didn't choose how to convert that data like it does with JPG, it's sometimes flat and doesn't look very nice.

However, some programs like Lightroom can do what is called 'non-destructive' editing. What happens is this:

Lightroom loads the raw file and de-mosaics it so you see an image. You can alter that image in many ways and Lightroom keeps a record of what you did in a special file so each time you load the raw file it also loads the special file and shows you the image as it would appear with your changes.

Once you are happy with all the changes you can then export a JPG from it. The raw file is still untouched, the special file still retains all the edits you made, but the JPG is there for you to do with whatever you want.

Final Bits

Now here's a beautiful thing. In fact 2 beautiful things.

First beautiful thing:

Every time you view a JPG you are actually decompressing the compressed file (remember I said earlier it's like a compressed zip file?) and when you close it you are re-compressing it. Every single time you do this with a JPG you lose a tiny bit more detail, this is called lossy compression. So over time the JPG deteriorates. If that happens or if you simply lose the JPG, you can go back and export another one from your raw file. There is no limit to how many you can export. You can even export one small JPG for your Facebook, a larger one for your blog and a much larger one to print out.

Second beautiful thing:

Let's say you miscalculated your exposure and it's slightly dark. No problem, use Lightroom or other raw processing software to give more exposure. Raw files allow you approximately 3 stops over and under. What they can also do is allow you to slightly darken a too-bright sky, but slightly lighten a too-dark shadow. Then when it's right, export your spot on JPG. There are a myriad of alterations you can make in raw software and the beauty is you can simply click 'reset' and your raw file is back instantly to how it was when you first transferred it from your camera. Both Canon and Nikon cameras all ship with their own software too so you don't have to buy a separate program if you don't want to.

You can't break anything and making digital costs you nothing, so why not try raw and see what you think?

Some extra bits...

JPEG (pronounced jay peg) stands for Joint Photographic Experts Group, who first determined how JPEGs would work. They're usually called JPGs simply because file extensions in Windows only used to be able to be 3 letters, hence myphoto.jpg. This is still the preferred and most commonly used file format, although often produced from a raw file. 

TIFFs are Tagged Image Format Files and they are not compressed like JPGs are, so take up lots more room. 

PNG is Portable Network Graphic. This format unlike JPG's does not lose info each time it is compressed and was made to replace the GIF which has limited or no use in photography. It's use is highly debatable. 

GIFs is Graphic Interchange Format and only contains 256 colours so is not usually much use to digital photography.