Firstly, let me apologise for the fact that it’s been so long since my last post. Life has been rather hectic recently, including the always-painful process of buying and setting up a new computer, but things are now back on an even keel again, and I plan to add post regularly once again. So, on to the subject of this post!
All good cameras give you the option of storing pictures either in JPEG format (the default), or using “Camera RAW” format. In RAW format, you’re storing (as the name suggests) the raw information from the camera’s sensor. RAW files are much larger than JPEGs, and they need to be processed on a computer before they can be posted online or transferred to a phone or tablet, but, nonetheless, there are excellent reasons why you should always shoot pictures in RAW mode, a couple of which I’ll go into in this blog post.
Firstly and most importantly, a RAW picture contains all the information from the camera’s sensor, as well as a complete record of the camera’s settings at the time the picture was taken. The camera I use most often, an Olympus EM1 Mark II “micro four-thirds” mirrorless camera, has a 12-bit sensor, which means that when a picture is taken, each pixel of the image records the brightness of that particular picture element in one of 4096 intensity levels for each of the red, green, and blue components of the pixel.
When you use the camera’s default action of storing a picture as a JPEG file, those 4096 intensity levels get reduced to 256 levels, which means that 94% of the information collected by the sensor is literally being thrown out. The computer inside your camera is pretty good at deciding which 256 intensity levels from the 4096 collected by the sensor it should retain, but it will never be as good as a human being at making such decisions, and once that information has been discarded, there’s no way to get it back again.
To illustrate the problem, consider the following picture I took at Philae temple in Aswan on 17th January 2019:
This picture has all sorts of problems! The camera’s light sensor has tried to cope with the fact that the portico is in deep shadow while the courtyard and pylon are in bright sunlight, but it’s finished up with the portico in shadow and the sky and pylon of the temple massively over-exposted. If I’d shot a JPEG image this picture would have been a dead loss; there would have been virtually nothing I could have done to recover useful information from it. Fortunately, however, I shot it in RAW mode, and using Adobe Lightroom (my preferred image processing processing application) I can reduce the overall exposure of the image to correctly expose the open court and sky, and then pull up the information in the shadows to see details on the column. When I do this, the picture looks like this:
It’s still no masterpiece, but now both the scenes on the column and those of the temple’s pylon are reasonably correctly exposed, and the picture is perfectly usable. I can now carry out other image processing to improve the picture still further (such as correcting the geometric distortions in the pylon and the column), but it’s the fact that the RAW image contains all 4096 intensity levels collected by the camera’s sensor that’s enabled me to recover from what at first seemed like a hopeless situation. The image still gets reduced to 256 intensity levels, of course, when I export it from Lightroom as a JPEG image, but now it’s me, rather than the computer inside my camera, who has decided which 256 of those 4096 intensity levels are the important ones! It took me no more than a couple of minutes to process this image.
Another situation where RAW images are hugely beneficial is when it comes to the white balance of a picture. The sensor of your camera always records a “colour neutral” image which, when the image is converted to a JPEG file, the computer inside the camera will change the colours of in accordance with the “white balance” setting of the camera in order to try to make the picture match the colours that the human eye perceives. Generally speaking, in ourdoor scenes the camera does a pretty decent job of getting the colours correct if you use the “auto white balance” setting, but it can get seriously confused when it comes to artificial light.
Philae temple is built from sandstone which is (unsurprisingly!) sand coloured. The camera does a good enough job of reproducing that when I take an outdoor picture:
But if I take a picture inside the temple where the scene is lit by fluorescent lighting, I end up with incorrect colours in the picture:
This is exactly the same type of stone that’s in the previous picture, but the fluorescent lighting of the scene has confused the auto white-balance setting of the camera, making the picture look a lot redder than it should be. If I’d been taking JPEG images, I’d need to manually change the white balance setting of the camera from “auto white balance” to “fluorescent” to get a proper colour balance in this picture, but shooting in RAW there’s no need to do that; I can adjust the colour balance in Lightroom to correctly match the colour I know the stonework should be:
(I’ve also increased the overall exposure and adjusted the geometry of the image here).
I hope these two simple examples have convinced you of the benefits of shooting in camera RAW mode rather than JPEG! RAW files can be manipulated on your computer to your heart’s content to get the very best out of your pictures, while JPEG pictures are “set in stone” and what you take is what you’re stuck with. I’ll be writing a lot more about image processing in the future, including the details of how to make the type of adjustment I’ve made to the images I’ve used here.
I’d love to hear your thoughts on this in the comments section below.