5 things you need to know before shooting raw files

18/10/2012

By Digital Camera Magazine

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Shooting raw files has become one of the most important photography tips we offer our readers on a daily basis. Yet while most photographers agree it's important to shoot raw files, the nuance of fine-tuning and editing raw files is often at the top of said photographers' list of most common photography problems. In this post we aim to demystify the experience of shooting and editing raw files by asking the question, 'What are raw files?' We'll also address four other key things you need to know before shooting.

Many photographers will have tried to shoot raw files because there's no doubt that you can end up with richer, more detailed images as a result. Left to its own devices, your camera will shoot in JPEG format, which, while certainly convenient, means that you automatically lose some of the original image’s detail. With raw, you don’t lose anything. Sadly, many readers will also have discovered that raw can be a pain in the rear. Images saved in raw can be huge, and they don’t always open 
in your photo-editing software. Frustratingly, camera makers can’t agree on a unified format for raw shots, which causes a lot of needless hassle.

The good news is that once you’ve got your head around shooting and editing raw shots, it’s 
a relatively painless process that can really take your photography to the next level. In this tutorial, we’ll start from the beginning, explaining the whys and wherefores of raw files. On the next page we'll address some of the most common questions about shooting raw and hopefully address some of your concerns.  

1. What are raw files?

 

To understand raw, it helps to know how a digital camera actually produces an image. When you fire the shutter, the image you take is recorded on your camera’s sensor, where the light is converted into an electrical signal that forms the image data. This ‘raw’ data is what makes up the majority of a raw file. Simple so far. What happens next differentiates raw files from the JPEG image format. The raw file is simply this image data, along with the information needed to construct the image, which is written to your memory card (find out how memory cards work). With a JPEG, before the image is written to the card the original raw data is processed (how it’s processed depends on what camera settings you’ve chosen, eg White Balance or a specific Picture Style). The file is then converted to JPEG format and finally written to your memory card. So, to recap: your camera produces raw files as a matter of course, but it’s up to you whether you let the camera process these for you to produce a JPEG, or whether you stick with the original raw file (check out these reasons why you want to shoot JPEG).  

2. Are all raw files the same?

No, and this is where much of the confusion surrounding raw files starts. Unlike JPEGs, there isn’t a standard for the raw files produced by most 
of the cameras made by big-name manufacturers. Each manufacturer has its own raw file format, and even more confusingly each model of camera 
has its own version of this format. So, current Canon cameras will produce a raw file with a .cr2 suffix, and the raw file from an EOS 1100D SLR will actually be slightly different to one from an EOS 7D. In use, these differences are only relevant if you’re editing files from more than one camera, or have updated your camera without installing new software on your PC, 
as the way that they work (and the way that you use them) will be the same. To further confuse matters, there is an exception to this rule. DNG is a file format developed by Adobe, which can be used by any manufacturer, but of the main SLR manufacturers only Pentax has included it on its cameras. Even if you use another brand of camera, DNG can still be a useful format, because it can be used as a 
way of opening raw images from new cameras in old versions of Photoshop and Elements. Raw files allow you to make subtle adjustments to colour without any loss in quality. Our image straight from the camera.

Our image after a few subtle adjustments:

3. Why can’t I view raw files 
on my computer without using special software?

Because a raw file is just a package of data – your computer doesn’t 
know what to do with it. Unlike a standard format, such as JPEG, a raw file doesn’t contain the information needed for your PC to decode it. Think of it like the words on a page: JPEG is like the finished article containing words, paragraphs and all of the correct punctuation; raw is like having all of the same letters written down, but not necessarily in the same order and without a structure that you can easily understand.  

4. So are raw files uncompressed?

 

Yes and no. Compression is a 
way of reducing the size of an image using complex maths. The important thing to remember is that there are two types – lossy and lossless. With lossy compression, as the name suggests, some of the image data is lost during the compression process. However, the files can be made much smaller than is possible with lossless compression. Some raw formats, such as Nikon’s .NEF files, can be saved 
in this form, as a way of achieving smaller file sizes, but this can result in lower-quality images, especially if they contain smooth tonal areas, like skies. All JPEG files use lossy compression. You may have noticed that when you save a JPEG you have 
to choose a quality setting. This is because the smaller you save the image the more information is lost, 
so a high-quality JPEG is a much larger file than a low-quality one. This quality loss can be acceptable if you only save the image once, but each time you resave the image more data is lost, reducing its overall quality. Lossless compression retains all 
of the data in the original file, but the resulting files are often only a little smaller than the original. Most raw formats use this type of compression to ensure that there is no loss in quality when you resave your files. Hence the higher image quality.  

5. What do 8-bit, 12-bit, 14-bit and 16-bit mean when it comes to raw files?

Every image you take contains a range of tones from pure black through to pure white, and the ‘bit-depth’ simply tells you how many different values there are. All JPEGs are 8-bit files, so they contain 256 tones, while raw images are usually 12- or 14-bit, 
so contain at least 4,096 tones. It’s generally considered that you need around 250 different tones to produce an image that appears smooth and natural, which is why the 256 tones 
in an 8-bit image are considered to be enough in most situations.

The problem comes when you start to manipulate the image using Levels or Curves in Photoshop. These commands compress or stretch an image’s tones, creating gaps in the image histogram that can cause unsightly banding or ‘posterisation’ in the finished image.

Using Curves or Levels on an 8-bit image can lead to a loss of tones, visible as gaps in the histogram display:

The greater tonal information of a 16-bit image means that you get a better quality result using the same adjustments:

This is particularly noticeable in areas of smooth tones such as a blue sky, where the steps between the different tones can become visible. With a raw file you start with many more tones, which allows you to make more extreme adjustments without these problems occurring (find out how far you can push a raw file). Photoshop 
can’t edit 12- or 14-bit files, so most raw editing software gives you the option of converting the image to 8 
or preferably 16-bit format. Why more bits equal more tones Bit depth 8-bit 12-bit 14-bit 16-bit Tonal values 256 4,096 16,384 65,536