Photographers interested in printing their pictures will usually record raw files at the same time as the regular JPEG format, and most serious cameras include a RAW+JPEG setting for this purpose. Advanced cameras let you choose the size and quality of the JPEG image so you can opt for the biggest and best JPEGs or the smallest JPEGs for online sharing and when storage space is limited.
Raw file advantages
When recording a JPEG image, 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 locked into the image file.
The processor then down-samples the image from 12 or 14 bits of information per pixel (as captured by the camera) to 8 bits (the default bit depth for JPEGs) and compresses it, discarding data that is unlikely to be missed by the human eye. Photographers have some control over JPEG compression through the Image Quality setting.
But JPEG compression is always ‘lossy’. Each time a JPEG file is re-saved, more data will be lost and the discarded data can never be recovered.
These images illustrate the main differences between JPEG and raw files. The top image has been cropped from a high-resolution JPEG taken with a 16-megapixel Micro Four Thirds system camera. The enlargement on the right shows how both highlights and shadows have been ‘clipped’. The lost details can’t be recovered. The lower image comes from a raw file recorded simultaneously with the JPEG. Note how much more highlight and shadow detail can be extracted from this file.
Raw files contain the image data as it is captured by the camera’s sensor. Nothing is discarded, even when the image processor compresses the raw file to make it smaller. The compression is ‘lossless’ which means all of the original image data is usable by the photographer for subsequent editing.
Shooting raw files gives you the option of converting them into 16-bit images which means the file has 65,536 levels of brightness per colour channel, compared with JPEGs, which provide 256 brightness levels per channel. Consequently, a raw file will provide much more latitude for making adjustments to brightness, contrast and colour levels before any processing artefacts become visible.
Raw files don’t have any white balance settings. The file is tagged”¨with the camera’s setting but the actual image data has not been changed.”¨So you can set any colour temperature you like without degrading the image. The same is true for contrast and sharpness adjustments ““ and also the image colour space.
These factors make it easy to correct errors in exposure, bring out details in highlights and shadows, remove colour casts and make your digital photograph look like the scene you envisaged. And, because it is done on your computer, there’s much more processing power available than a camera can possibly provide.
Raw file disadvantages
The main problem with raw files is that most of them 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 one manufacturer’s range. Each variation requires different software to convert the raw files into editable formats.
Fortunately, raw file converters have also been developed by third-party software developers like Adobe (Camera Raw) and PhaseOne (CaptureOne)”¨and there’s a freeware application, RawTherapee. But it takes a while for them to reverse-engineer the proprietary raw formats so they can take a few months to support just-released cameras.
A few camera manufacturers use”¨ the ‘open’ DNG (digital negative) standard developed by Adobe, among them prestigious brands like Leica, Hasselblad and Sinar, as well as Ricoh.
Pentax offers a choice between its proprietary pEF.RAW format and DNG.RAW. Other manufacturers, such as Apple and Google, also support the DNG.RAW format in various ways.
Raw files are also large, even when they are losslessly compressed. A typical 16-megapixel camera can produce raw files that range from approximately 15MB to 100MB (depending on the amountӬof detail in the shot and the degreeӬof compression the camera applies), compared with 9MB to 18MB for a high- quality JPEG shot of the same subject.
You can store fewer raw images onӬa 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.
This illustration shows the difference in sizes between a JPEG and a raw file recorded simultaneously. Note the amount of image metadata (information about the image) available with the JPEG file and the ability to display a preview thumbnail. Neither is available, with raw files, even if they are in the non-proprietary DNG format.
Having to convert your images from raw to an editable format (JPEG or TIFF) adds an extra step to your workflow.”¨If this is irksome, you’re probably better off shooting JPEGs ““ especially if you don’t print your shots any larger than A4 size.
Raw file conversion
All raw files require subsequent editing so, unless you want to edit your digital images, there is little point in shooting raw files. Editing raw files is a two-stage process because raw files must first be converted into an editable format (either JpeG or TIFF), zo raw file shooters must make sure any raw conversion software or image-editing application they buy supports the raw images from the camera(s) they plan to use.
A good raw file converter will integrate effectively with your workflow ““ and”¨your favourite editing software. It should include a raw file browser and the ability to apply settings from one image to a group of other images (batch processing).
The bundled raw file converters supplied with Canon (top) and Olympus (below) cameras provide good image viewing and management facilities plus useful tools for converting raw files into editable TIFF or JPEG formats.
Because the performance of bundled software varies between good, acceptable and frustratingly limited, many photographers prefer third-party applications. One of the best ““ and most popular ““ is Adobe Camera Raw, which is included in the latest versions of Photoshop, Photoshop Lightroom and Photoshop Elements. This application supports virtually all raw-capable cameras on the market – although it may take several months for new models to be included and you may need to update your version of Camera raw by visiting the Adobe website when you buy a new camera.
The user interfaces for three popular raw file converters are shown here: from the top ““ Adobe Camera Raw,Phase One Capture One,RawTherapee.
Popular third-party converters include Phase One’s Capture One and RawTherapee. Trial downloads of the adobe products and Capture One are available from the developers’ websites. RawTherapee can be downloaded free of charge and makes a good partner to GIMP, which is also freeware.
[The Silkypix software bundled with Fujifilm and Panasonic cameras has consistently delivered sub-standard results in Photo Review’s camera tests. Consequently, we recommend readers to avoid using it.]
Essential adjustments
With any kind of image editor, youӬn eed plenty of scope to adjust image brightness, contrast and colour qualities. These functions are also vital in a good raw file converter.
Exposure adjustments should include selective controls for highlights and shadows (and/or whites and blacks) as well as overall brightness adjustments. Histogram displays (preferably RGB so you can see how well the colour channels are in balance) make it easier to see when colours are unsynchronised and likely to produce unattractive colour casts.
The Highlights slider lets you darken very light areas and can help youӬto pull some colour back into bright skies. The Shadows slider adjusts dark image areas. Drag to the left to darken shadows or to the right to brighten shadows and recover shadow details.
These illustrations shows how the Shadows and Black sliders can be used to bring out details in deeply shadowed areas of an image without affecting other tones. The lower image is the adjusted image, with the sliders circled in red.
The Whites slider adjusts white clipping but only works when whites are only slightly clipped. To reduce clipping in highlights, drag the slider to the left, while to increase clipping specular (totally white) highlights, such as metallic surfaces, drag the sliderӬto the right. The Blacks slider adjusts black clipping in a similar fashion.
Colour adjustments should include sliders covering white balance, saturation and individual corrections for the red, green and blue colour channels as well as the ability to add or remove colour casts via a ‘Tint’ slider. White balance pre-sets can also be handy.
This illustration shows the straightening tool and white balance pre-sets in Adobe Camera Raw circled in red.
Other useful tools include aӬClarity slider, which enhances Ҭmidtone contrast, thereby making images appear sharper. Photoshop applications also include a Vibrance slider, which boosts saturation in duller colours while backing off on those that are already vibrant and colourful.
Noise removal and sharpening tools can also play important roles when converting raw files, even thoughӬthese tools can be found in mostӬimage editors. The same is true for a straightening tool. Starting out with some preliminary corrections means potential problems are less likely to be amplified in subsequent processing steps.
Good RAW converters should alsoӬbe compliant with colour management. You should be able to choose between at least two colour spaces (generally sRGB and Adobe RGB 1998). Batch processing should also be supported and is a real time saver when you have many files that all require the same corrections.
Correcting lens aberrations is easy when the raw conversion software contains the camera and lens profile (circled in red).
Photoshop applications also include lens corrections for aberrations such as distortion, coloured fringing and vignetting (edge darkening). These are corrected automatically when camera and lens combinations are stored as profiles in the software. Simply select the profile and the job is done.
Saving files
When you’ve made all the necessary adjustments to the raw image it must be saved in an editable format. Most raw converters let you choose between JPEG and TIFF (Tagged Image File Format) and you can choose 8-bit or 16-bit for TIFF files.
Selecting 16-bit tTFF gives you the maximum amount of data to work with. This is the best option when you plan”¨to make additional adjustments in any image editor. It’s also the best choice for image files that will be archived or printed.
Choose JPEGs for images that will be posted online or attached to emails or displayed on computer or TV screens. Note that virtually any image editor will make it easy to convert TIFF files into JPEGs with almost any size and quality level.
Useful links
www.bit.ly/raw-file-converters
www.bit.ly/raw-converter-selection
Excerpt from Photo Editing Pocket Guide
