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Part 8 : Introducing white balance and shooting in RAW

*Disclaimer: Notes written by Alistair Keddie.

 

Introducing DSLR White Balance and RAW shooting settings, photography notes

 

 

Part 8 : White balance


colour balance settings found on a DSLR Camera

White balance is all about making white look white under the many different lighting conditions we encounter. For instance, the colour temperature of light is different if we are reading by candle light than if we are standing in shade. Likewise, fluorescent lighting has a different colour temperature than daylight, or tungsten light. This temperature is measured in degrees kelvin but, for us, this translates as being the colour tint or cast that can lend to our exposures. The warmer the light source, the redder it becomes (such as at sunset or by candle light). The cooler the light source, the bluer it becomes (such as standing in deep shade). By adjusting the white balance setting we instruct the camera to compensate for any colour casts made by the available light. Most of the time, Auto White Balance will work sufficiently well but on certain occasions, we will need to adjust this ourselves. Its especially important to pay attention to white balance if you are shooting in JPEG format as any mistakes will be embedded in the file and harder to remove later. For instance, if you are shooting under indoor lighting with the white balance set to shade the image will have an orange cast. This is because the camera expects light in the shade to be at the blueish end of the spectrum and attempts to warm it up a little so that white still looks neutral.

In RAW format we can pay less attention to white balance as it is not fixed and can be easily changed later. Our camera also has a Custom White Balance setting. This is usually set by using a mid tone grey card (the same as we’d use for exposure) which you photograph and then select. Refer to your manual for instructions on how to do this, but is usually found in one of the menus.

 

a strip of different colour balances in a single photograph taken on a DSLR Camera

 

RAW versus JPEG


RAW and JEPG are both file formats used for storing images on our camera. The biggest difference between them affects the absolute quality of the final image and choosing which format to shoot depends on our output needs. Are we shooting for fast output and turnaround or for images that require additional processing and creative control to capture the highest possible quality? Its a matter of choice, workflow and the type of shooting we are doing. JPEG is definitely suited towards fast turnaround whilst RAW captures the highest possible amount of image information.

When capturing a RAW file the camera is doing pretty much what the name suggests. It takes all of the image data captured by the sensor and writes it more or less unchanged to the memory card.

When the camera makes a JPEG file, it still captures a RAW image but this time makes various adjustments to colour, saturation, tone, contrast, etc, aiming of course to output a good quality image based on the built in processor. It embeds the white balance and any highlight and shadow clipping and then compresses the image data down by throwing away most of the data gathered. JPEG is a lossy format and because of this you should always use the highest and finest resolution possible. Straight out of the camera though, JPEG’s will often look better than RAW which require further work.

RAW files are much bigger than JPEG’s so require higher capacity memory cards for the same number of shots. To understand why they are so much bigger and why they offer much better quality it’s necessary to understand a little about bit depth. This refers to the number of possible values, or levels each pixel in our image may hold.

For instance, in an image described as having a bit depth of one, each pixel can have two possible values, that is, be either black or white. In a two bit image, each pixels has four possible values, that is, 1 : two white plus two black(giving a mid tone grey), 2 : one white plus three black (giving a dark grey), 3 : one black plus three white (giving a light grey) 4 : four white (giving pure white) four black (giving pure black). Our two bit image can then contain four possible tones.

As the bit depth increases, so too does our range of possible tones. A JPEG image is described as an 8 bit image. This means that it has 256 possible values. 0 is black, 255 is white and the other 254 are shades of grey. This holds true for a grey scale image which is composed of a single channel. However, if you remember our section on the histogram, a colour JPEG is composed of three channels, one for red, one for blue and one for green. Colour JPEG’s are described as 24 bit colour (8 bit x 3 = 24 bit). Knowing that each 8 bit channel contains 256 possible values, we can work out the range of possible values contained in a 24 bit file, its colour palette, by multiplying 256 x 256 x 256. This gives us a figure in the region of 16.7 million colours.

And that sounds huge until you compare it with a RAW file. Most current camera sensors are 12 bit. According to the maths, this has 4096 possible values between black and white. Thats black at 0, white at 4095 and 4094 possible shades of grey in between. Multiply that by the three colour channels to create a 36 bit image and it works out at a possible colour palette of 68.7 BILLION.

But what does all this mean in practice? It tells us that a RAW file captures vastly more image information than that captured in a JPEG. This becomes important when we want to process our images on the computer. For instance, by pushing the tonal range, increasing the contrast, recovering detail from highlights or shadows, strengthening or weakening colours, converting to black and white or any of the other things we might want to do.

JPEG images will begin falling apart much faster than RAW because they have so much less information to work with. Colours and tones will begin to break up much more quickly when we make adjustments as JPEG’s only have 256 tones to work with, as opposed to the 4096 tones captured in RAW.

What becomes clear is that RAW is the format of choice for images you want the absolute best quality from. It is in effect, your digital negative and should be used for those shots you go to great lengths to get or need to get the best from. JPEG is the format you use when you require speed, such as in events photography where you need a quick turnaround.

JPEG is also the format you use when you need to send your photographs online fast. However, bear in mind that JPEG’s can be output from your RAW if time allows. You can also set your camera up to take RAW and make a JPEG duplicate. Useful for shoots where you need the quality later but need to show results quickly.

RAW is also a very forgiving format for beginners as its much easier to correct your mistakes. For instance, white balance is not fixed in RAW and can be easily adjusted. Likewise, you can often recover much more detail from areas of highlight or shadow clipping, detail that is often lost in JPEG. In fact, all around, RAW opens up a huge world of creative possibilities when we take our work into the digital darkroom.

Each manufacturer has created their own proprietary RAW format. Canon RAW is different from Nikon RAW is different from Sony RAW etc, and a question arises around RAW’s future compatibility. How do you open your files years from now if the manufacturer has disappeared and their particular file format is no longer supported? To address this, Adobe has created the DNG format. This is a free and open source, in effect, future proof. You can download the free DNG Convertor from Adobe and use this to convert your RAW files. This even allows you to elect to embed the original RAW file within the DNG in case you think you’ll need it again. DNG itself is a very stable format and works well with any of the Adobe suite of software.


 


 

 


 

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