Wednesday, 6 March 2013

Why use RAW?

You'll often hear people recommend to use the RAW image file format. But why? What is the reason for using the RAW file format? In this artice, I'll look at an example where it makes a difference.

Most serious cameras have the possibility to record the images in two different file formats: JPEG and RAW. The RAW file format can be of many different types and extensions, but they all have some things in common: The RAW files take up much more space than the JPEG file, and they contain the image as seen by the camera sensor, mostly without any adjustments.

This is in contrast with the JPEG files, which are compressed to take up less space, and where the camera has tried to interpret the image how it thinks you want to see it. With the RAW file format, you can later develop alternative JPEG output files by altering how you want the original RAW file to be interpreted.

Here is an example JPEG image. It was taken with the Panasonic GH2 camera, with the Lumix G 14mm f/2.5 lens at ISO 640, f/2.8, 1/10s.



The shutter speed is too slow for taking a picture with this lens, according to conventional wisdom: To be reasonably sure to avoid camera shake blur, one should use around 1/30s or faster with a wide angle lens like this. However, in this case, I preferred to use a slow shutter speed, and avoid using the flash or a higher ISO. Using the flash would have changed the style of the photo totally. Besides, I like the effect of the slow shutter: The trailing lights from the sparks coming out of the pipe can be seen. And the image is still reasonably sharp.

The picture was taken late dusk, which is what gives it the blueish tint. The blue colour is correct: The scene was in fact blue due to the timing, just after sunset. However, by using the setting "Twilight" in the RAW developer program Silkypix, I can get more natural looking colour tones:



This image has a totally different appearance, with more normal skin tones, and less blue.

One could also go the other way, and exaggerate the blue dusk colours, by changing the white balance and increase the saturation:



Some would say that the colours now look unnatural, others might prefer it for the stronger colours. But the point is that when you have the RAW image, you are free to make these choices later. With only the JPEG image, it is more limited what types of adjustment you can make, without significantly losing colour details.

With that said, you are less likely to want to make colour tone adjustments to images taken in daylight, with a proper exposure. In those cases, you are often well served with the JPEG image only. In my opinion, the RAW image is of more use when the there is dim light, and when the exposure is uncertain. In sufficient daylight, with normal contrast, the camera often does the right choices with the out of camera JPEG image.

1 comment:

  1. Hey guys! Really well done piece on JPEG / RAW. Thanks for presenting both sides to show how it's not an "either this OR that" but rather an option to help the shooter make the best image under the conditions. Thanks very much.
    Will C.

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