Raw vs JPEG Capture

Raw files contain the image data as it is captured by the camera’s sensor with only minimal processing applied. Many photographers liken them to ‘digital negatives’ because they must be processed on a computer using special software to yield optimal results. They’re quite different from JPEG images (the universal file format for digital images) and have significant advantages for serious photographers.

JPEG vs Raw Files
When you capture JPEG files, the camera’s microprocessor converts the raw image data into RGB pixel values (a process known as demosaicing) then applies white balance, saturation, sharpening and other adjustments according to pre-determined formulae. These settings are effectively locked into the image file. The camera’s on-board microproscessor then compresses the image and downsamples it from 12 bits of information per pixel (which is captured by the camera) to 8 bits. Some image data is lost during this process. The more the image is compressed (by adjusting the Quality setting), the more information is discarded.

When you shoot raw files, the full 12 bits of information per pixel recorded by the camera is retained. Furthermore, YOU take control of the white balance, saturation, sharpening and contrast adjustments during the conversion process, which is done on your own computer. This allows you to recreate the colours and tones in the image to match your memories of the subject. Although it may be difficult to see much difference between a high-quality camera-processed JPEG image and a post-processed raw file when you make an A4-sized print, shooting raw files will allow you to extract every bit of potential from your shots. In some circumstances, it can even make the difference between a useable shot and a write-off.

Many of the latest DSLR cameras have a RAW+JPEG setting that allows JPEG files to be recorded simultaneously with raw files. This feature is handy when you’re not sure about the end use for your pictures. However, when you have to store both file types together you need to be sure you have enough memory for a shoot as the combined files take up roughly twice the space of a high-resolution JPEG file and one-and-a-half times the space of a raw file.

Many cameras allow users to select from a range of JPEG file sizes in the RAW+JPEG shooting mode. Users can opt to capture a raw file with either a high-resolution JPEG or one with a lower resolution. The lowest JPEG resolution is ideal for images that will be emailed or posted on the web so this function can prove a time-saver for anyone who wants images for printing as well as online use.

Many DSLRs allow users to record raw files and JPEGs simultaneously, using the RAW+JPEG setting.

Raw Format Plusses and Minuses
The main problem with raw files is that they are proprietary. Not only is Canon’s format different from Nikon’s, Olympus’s and Sony’s and everyone else’s, but raw formats may also vary from model to model within a manufacturer’s range. Consequently, photographers who plan to shoot raw files must make sure any raw conversion software or image-editing application they buy supports the raw images from the camera they plan to use.

Unfortunately, it can take several months after the release of some new cameras before the camera manufacturer has supplied the necessary software development kit to third-party raw converter developers like Adobe (whose Camera Raw converter is one of the most frequently-used raw converters). In the interim, you will be stuck with the software supplied with the camera.

Raw files are also relatively large. For a 10-megapixel camera, file sizes range from approximately 8MB to 30MB (depending on the amount of detail in the shot and the degree of compression the camera applies), compared with around 2.5MB for a high-quality JPEG. This means you can store fewer images on a card and it will usually take longer to transfer image files to your computer. It may also reduce the continuous shooting capacity of your camera as the buffer memory will fill up sooner.

Having to convert your images from raw to an editable format (JPEG or TIFF) adds an extra step to your workflow. However, because you take control of the conversion process you can adjust each image individually. Most raw file converters also provide batch processing facilities so you can process groups of shots that require similar adjustments.

When you convert your raw files into editable formats (JPEG or TIFF) the processor may allow you to correct exposure-related problems – provided the required adjustment is within the parameters of the raw conversion software. Finally, you can output the image as a 16-bit TIFF file, which gives you a robust platform for further editing.

Most raw converters allow you to recover highlight detail in images that have been overexposed by up to one stop. In contrast, there’s not much you can do with an overexposed JPEG image. If no highlight detail was captured, no amount of editing can bring it back. In the case of under-exposure, most raw converters provide a similar latitude for detail recovery and the resulting image should not be excessively noise affected. In contrast, recovering shadow detail from an under-exposed JPEG usually results in visible shadow noise.

Raw File Converters
A good raw file converter will integrate effectively with your workflow – and your favourite editing software. This integration should include a raw file browser and the ability to apply settings from one image to a group of other images. An example of an excellent third-party browser is Microsoft’s RAW Image Thumbnailer and Viewer, which allows users of the Windows XP operating system to view, organise and print raw images from supported Canon and Nikon digital cameras (but not from other manufacturers as yet). It can be downloaded free of charge from Microsoft’s downloads library (go to www.microsoft.com/downloads and key in Raw Image Viewer). It’s a valuable tool for checking raw files as it displays some of the image metadata.

Several popular software applications come with raw file converters. One of the best is Adobe Camera Raw, which is supplied with the latest versions of Photoshop and Photoshop Elements. The latest versions of Corel’s Paint Shop Pro and Ulead PhotoImpact also support raw file editing from many recently-released cameras, as do the freeware applications, Picasa (www.picasa.google.com) and Irfanview (www.irfanview.com).

When JPEG is Better
In general, raw files are at least twice as large as JPEG files shot at the highest resolution and quality settings your camera supports so, if storage is limited, you should think carefully before selecting the RAW setting (and even more carefully about selecting RAW+JPEG) on your camera. There’s also little point in shooting raw files when the images are destined exclusively for use on websites and in emails as they must be converted to JPEGs before they can be posted online. Shooting raw files is also pointless if you don’t plan to take advantage of the facilities they offer for editing image files.

Many panorama stitching programs can only be used with JPEGs. It is also unlikely that anybody could see much difference between images shot as JPEGs and those captured as raw files unless the shots covered an extended brightness range and/or unless they were enlarged considerably. However, for maximum quality and control, use of your camera’s raw file format is recommended – especially if you want to make top quality, poster-sized prints.

TIFF Conversion
Although few modern cameras include it as a shooting option TIFF (Tagged Image File Format) is a useful file format for image editors as it supports a much higher bit depth than JPEG. Whereas JPEG files are limited to eight bits, which uses one byte per pixel and can reproduce 256 colours in all, most DSLRs record 12-bits (4096 colours) in their raw files. These files can be converted to 16-bit TIFF files that are capable of rendering 65,536 colours.

Shooting raw files and converting them to 16-bit TIFF files allows you to capture the maximum tonal gamut your camera’s sensor can record and utilise it to extract the widest possible tonal range in your prints. TIFF files are at least three times the size of the highest-resolution JPEG images, but PC data storage today is relatively inexpensive and it’s a small price to pay for the control you have over the final output quality.

TIFF files also give you a much better starting point for image editing. With a higher bit depth, you can apply a greater range of adjustments without compromising picture quality. The illustrations on the next page show how much data can be lost when you edit a JPEG image, compared with a 16-bit TIFF file. The gaps in the histogram for the JPEG image represent data that has been lost through editing adjustments. No data is sacrificed when the same adjustments are performed on a 16-bit TIFF image.

Editing Software
Raw file converters vary from powerful, intuitive and easy to use to downright frustrating. The most popular universal raw file converter is Adobe’s Camera Raw, a plug-in for recent versions of Photoshop and Photoshop Elements. It is supplied as part of both applications and also downloadable from Adobe’s website www.adobe.com). Photographers who purchase new cameras that are capable of raw file capture should check this site for updates to Camera Raw as new cameras are being added as they are released (however, it can take a month or so for the latest models to be included.)

The histograms to the left of the picture show the effect of a Levels adjustment on an 8-bit JPEG image produced from a raw image file (top) and the same adjustment on a 16-bit TIFF file (below) produced from the same image. Note the comb-like effect on the JPEG histogram. Image data is lost at each gap in the graph.

While the raw file converters supplied with DSLR cameras generally allow photographers to convert raw images into 16-bit TIFF files, care must be taken when selecting an image editing application for further adjustments. The simplest image editors are usually restricted to 8-bit files so DSLR photographers who plan to shoot raw files can only work with the more sophisticated applications.

Applications that support 16-bit TIFF files include Adobe’s Photoshop and the latest versions of Photoshop Elements; Corel Paint Shop Pro, The GIMP and Ulead PhotoImpact. The GIMP is a freeware application, while Photoshop Elements, Corel Paint Shop Pro and Ulead PhotoImpact are affordably priced and Photoshop is a professionally-priced package. Note that while freeware applications are often very capable, the level of support is negligible, whereas purchased products tend to provide a high degree of online support. Photographers who lack the necessary computer experience should stick with programs like the Adobe, Corel and Ulead packages.

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