Shooting in RAW

Since there has been an amount of discussion in the forum lately regarding this subject, it occurred to me that some may have been left in the dark when it comes to "shooting in raw format". Not all cameras will have the facility for raw format and even if yours has, you may not be using it. Either you don't understand what it does, or you are happy with the format you use now. This tutorial may explain the concept of RAW format and enable you to make a more informed decision as to whether or not RAW is for you.

A digital Camera records each image you take on a sensor chip, either CCD ( Charge-Coupled Device) or CMOS ( Complementary Metal-Oxide Semiconductor). When I say records the image, I do not mean in the same way a film records it. The sensor will record the amount of light that hits each pixel and this is recorded as a voltage level. The camera will then change the voltage signal into a digital representation, there is little point in explaining the system behind this change as you would fall asleep and never finish reading, so I will stop the techie bit here.

If you have the camera set to record your image as a JPG and not RAW the camera's built in software will make some automatic decisions on how your photograph should look before it is downloaded to the computer. Firstly it is important to understand that a sensor (CCD or CMOS) can not record colour, unless it is a Foveon chip which uses three layers, one for each primary colour, however not too many cameras use these. The colour is rendered by placing colour filters over each pixel (Red Green or Blue). Half the pixels are coloured Green and the other half are either red or blue. Using a very complex system these pixels are compared with their neighbouring pixels and the colour is produced.

The camera will also make other decisions such as contrast, sharpness and colour saturation. It also compresses the image quality and converts it to 256 brightness level. Compressing the image is the final setting for a JPG file. This means that in order to produce the smaller file (which is the reason JPG format is used) some of the recorded data will be discarded by the camera. If the compression is set low, very little information will be lost and it will be almost impossible to detect with the human eye. Set it too high and the resulting image quality will be low and disappointing.

When the camera is set on RAW, the camera creates a header in the image file which, stores the same saturation, contrast and sharpening levels but does not apply these to the image. In other words your camera makes no decisions about how the image should look, but holds on to this data within the header, this is known as the RAW data. On most cameras, when using RAW, there is no compression, even if there is, it is very low. NIKON, for instance uses a slight compression but not appreciable loss of quality can be detected.

When your RAW image is loaded onto your computer it will not normally be able to be read by many image software, including PhotoShop 7 or lower and Paint Shop Pro. PhotoShop CS now has raw data readers included and plug ins are available for PS7. Assuming your software can read the RAW data you will be presented with the facility to make all the decisions that your camera would have made as a JPG.

The interface below is taken from Raw Shooter essentials, this has now been discontinued as it was bought out by ADOBE. I now use CS3 and the RAW converter included.

As you can see on the right of the interface one has several choices to make including Colour temperature, shadow detail sharpness etc. The image you see in the centre has had none of these changes added yet and is therefore still in raw format. The image below shows the changes I have made before it is saved. Once saved, I can then open the image in PhotoShop and manipulate the image with all the tools available to me. It is not possible, even with the raw plug in, to use PhotoShop's tools on the raw image.

The sliders on the right will give you some idea of the decisions I made on the RAW data. Remember, this is not the finished image, all the fine detail will be sorted in PhtoShop. This is, if you like my working (rough) file. The finished image will be shown later.

So, A RAW file is the data recorded by the camera, with a few extra bits added but no compression or decisions made as to how the file will look. A JPG file is one that has had the camera apply white balance, contrast, and saturation, and then has had some level compression applied, along with linear conversion, matrix conversion, which I have chosen not to go into for the sake of both our sanity.

Reasons to use JPG

• Files are smaller and will not use up all your card space.
  
• For most applications a JPG will be sufficient quality.
  
• Not so much work to be done before you print or send off to Aunt Sally for her family album.
  
• Some cameras can not record RAW files or the camera works more slowly.

Reasons to use RAW

• Raw files do not have a colour balance. Even if your camera is set to apply a specific colour balance, the information will only be stored in the data but will not apply that change to the image. Using the RAW colour balance conversion is more adjustable. Once the JPG colour balance is set, the white balance is not easily adjusted.
  
• There is no compression to the image. Once the JPG is set each time you save the file, a certain amount of quality will be lost. From the RAW file it can be saved on your computer as a TIF or PSD file, when you make changes to either, no quality is lost. So the photographer can produce the highest possible quality in the image.
  
• The RAW file is never changed. When you make the decisions in the RAW interface, the changes are only stored in the RAW data, you can always go back and work again on the RAW file.
  
• The biggest advantage is that the RAW file is a 16 bit image, this gives you 65,536 levels to use. The JPG converts the 16 bit image to 8 bits and only 256 levels. It should be noted that some tools in PhotoShop will not work on 16 bit images and will therefore have to be converted to 8 bits, however this still leaves you with an uncompressed file.

I could continue with the advantages of RAW but I hope I have given you food for thought. All digital cameras shoot a RAW image, some will allow you to keep the RAW state, others will not give you the choice. If you can choose, and you decide to pick the JPG, your are committing the image to decisions made by the camera. With a JPG file you are committing yourself at the time of exposure to several of the most important aspects of image quality, namely white balance, overall contrast, colour saturation and the like. With a raw file you make decisions about these settings at yourself. Can you trust the camera to make the right decisions?

And Finally, the finished image, after RAW and PhotoShop work.



Beach Huts in Thorpe Bay
Some local saturation added. Levels changed in PS cropped, resized and sharpened.