JPEG vs TIFF vs RAW

One of the first things my tutor said to me when I embarked on Digital Photographic Practice was always to shoot in RAW. I can honestly say that I have never set my camera to RAW so I suppose now is the time to try. I realise it is covered in the course in part three but I thought I might research it beforehand and try to understand better the file formats available and their relative pros and cons.

JPEG stands for Joint Photographic Expert Group and it defines a way of compressing digital images. In the simplest terms, it does this by getting rid of what the algorithm considers to be redundant data. Because data is discarded or lost it is referred to as a “lossy” method of compression and because of this data loss, repeated saving of a JPEG will incrementally lose more detail and result in amplified compression artefacts. It can also result in larger file sizes. You can choose the amount of compression but more compression means more data is thrown away.

TIFF stands for Tagged Image File Format. It can be either compressed or uncompressed and, unlike JPEG, the compression is lossless. This means it has none of the disadvantages of JPEG but results in much bigger file sizes. Wise advice when working on a JPEG is first to save it as a TIFF. Then, multiple takes can be made in processing the image without degrading it. As my camera cannot produce TIFF files directly, I will not consider them further.

RAW is a digital file based on the data exactly as it comes from the sensor. It is not a picture format so cannot be viewed without a RAW converter and a Canon RAW file will be different to that of a Nikon. Being an uncompressed format, the RAW file is much bigger than a JPEG.

To produce a JPEG the camera processes the RAW data from the sensor according to the settings the user has applied. This will generally involve white balance, sharpening, adding blacks, brightness and contrast and noise reduction. The output will then be a file that can be used straight away or further manipulated with image editing software. Being a smaller file gives the JPEG format two further advantages, you can get more image files on a given size of memory card and (particularly important for sports and action photographers) the camera will have a much higher burst capacity.

And the advantage of RAW? Apparently, it can give you higher quality.

So what format should I shoot in? A question whose answer up to now has been resoundingly in favour of JPEGs. I have appreciated the extra storage and a lot of my photography is with sports and animals so I have taken advantage of the burst capacity. Furthermore, I have not had need of the reputed extra quality a RAW file can give.

To counter the obvious advantage of JPEGs, an investigation of RAW should give an explanation of the extra quality, how that quality compares to a JPEG and what processing is required to achieve it.

Perhaps the biggest advantage is the bit depth available. Each pixel of a camera sensor typically uses 12 or 14 bits to record the brightness of the light falling on them. During the conversion to JPEG, this gets reduced to 8 bits. When there are insufficient steps in a brightness scale, there can be a perceptible jump between adjacent steps, known as banding or posterisation; any levels adjustment to correct a poorly exposed image will reduce the number of steps, bringing posterisation closer. With 8 bits, there are 256 steps from minimum to maximum brightness; this is generally sufficient to avoid posterisation but it is clear that a RAW file with its greater bit depth will give much more available headroom. This makes a RAW file much more amenable to exposure correction than a JPEG and is the reason behind the oft quoted advice to use RAW when you might not be able to get the exposure spot-on.

Another commonly touted advantage is being able to use more powerful algorithms and greater computing power to process the RAW image. The data that comes off the sensor is raw, in the sense that it has not been processed. The camera uses a built in processor to convert that data, based on settings that are either built in to the camera or applied via the user interface, into the JPEG that is displayed. With a RAW format file, the raw data is saved and the settings saved as metadata in a file header. This means that the processing can occur later, either using the saved settings or other, user defined, ones. This processing will not be restricted to the computing power and software available in the camera and can be under the total control of the photographer. Features like sharpening and white balance in particular are quoted as potentially benefiting from the RAW workflow.

The output JPEG file will have a pre-determined colour space, such as sRGB or Adobe RGB. The RAW file records the output of each photosite in the sensor and this will contain more colour information than any pre-defined colour space. RAW image converters can use a much larger colour space to take advantage of this. This means that images can be processed with much greater colour fidelity and colour space need not be defined until necessary for the output device.

Photostackexchange contains some impressive examples which graphically portray the advantage of RAW:
JPEG straight out of camera Reworked RAW file Reworked JPEG
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Out of the camera, the jpeg is flat and lifeless, the reworked JPEG has restored the colour nicely and probably as well as the RAW file but the clipped highlights in the sky is beyond its range.

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The JPEG looks a lost cause and only worthy of binning. Yet there is still remarkable detail in the RAW file which can be recovered.

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At first glance the reworked JPEG is a useful picture but note the subtle variations in tone in the RAW file, particularly in the groom’s trousers and waistcoat. There is also some banding in the highlight on the back wall due to the heavy recovery needed in the JPEG.

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Here the RAW file is a much cleaner sharper image with more saturated colours and better contrast.

I mentioned earlier that you cannot see a RAW image and you need a converter to be able to view it. The same RAW converter can be used to process it. Typically they are provided by the camera manufacturer, Adobe also bundle ACR (Adobe Camera Raw) with their photo-editing packages and there are a number of independent software houses producing them. RAW converters are improving all the time and it is always worthwhile checking the market and making comparisons.

I have two options to open and process RAW files; Adobe Camera Raw which is bundled with Photoshop Elements and Canon’s Digital Photo Professional, provided by the camera manufacturer. I have tried using both. The problem is that I have a reasonable familiarity with Photoshop, to learn something new inevitably leads to comparisons and the thought that, “I know how to do that with Photoshop!” It’s going back to the bottom of the learning curve. This series shows some of the potential even from the bottom of the curve.

JPEG from the camera

Processed JPEG

Processed RAW and saved as TIFF

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Out of the camera, the jpeg has blown highlights in the curved ceiling and little detail in the shadow, particularly the girl’s hair in the foreground left. This has been fairly heavily reworked in Photoshop, particularly to restore the ceiling. This had to be selected to avoid darkening the rest of the image and the division can be seen around the foreground girl’s head. This was very quickly done in ACR using the exposure tools. The ceiling is better, there is much more detail in the girl’s hair and the colours are more vibrant.

The information for this post and further reading on the subject can be found here:

http://www.slrlounge.com/raw-vs-jpeg-jpg-the-ultimate-visual-guide

http://digital-photography-school.com/raw-vs-jpeg

http://www.cambridgeincolour.com/tutorials/imagetypes.htm

http://www.cambridgeincolour.com/tutorials/RAW-file-format.htm

http://www.luminous-landscape.com/tutorials/understanding-series/u-raw-files.shtml

http://photographyconcentrate.com/10-reasons-why-you-should-be-shooting-raw/

http://digital-photography-school.com/should-you-be-shooting-raw

http://photo.stackexchange.com/questions/2627/good-examples-of-raws-advantages-over-jpeg

http://dpbestflow.org/camera/raw-vs-rendered

http://www.bythom.com/qadraw.htm

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