Raw file converters

The main workspace in Adobe Camera Raw.

A good raw file converter will allow you to correct errors in exposure, adjust brightness levels to ensure both highlights and shadows contain detail, remove colour casts and, generally, make your digital photograph look as much like the original scene you photographed without losing any of the fine tonal nuances that make the difference between an excellent digital picture and a poor one. And, because all adjustments are done on your own computer, you have much more processing power at your fingertips than the camera can possibly provide.

Unfortunately for photographers, the capabilities of conversion software vary widely between different manufacturers. Some have intuitive user interfaces; others are clunky. Different manufacturers provide different adjustments and different levels of adjustment.

Nikon, for example, bundles a very basic converter (ViewNX2) with new cameras but charges more than $200 extra for its more powerful and capable converter: Capture NX 2.

Raw converters are constantly changing, usually for the better. Many recent converters include noise reduction algorithms and corrections for chromatic aberration, rectilinear distortion and vignetting.

Unfortunately, to take advantage of these features you have to keep pace with developments. You’ll probably need to update converters each time you buy a new camera body ““ and this can prove costly.

Third-party converters are popular with both professional photographers and serious enthusiasts, with Adobe Camera Raw (ACR) and Phase One’s Capture One being the leading products. ACR is a free download for users of Photoshop and Photoshop Elements but you must have the latest version of each application installed. This requires regular updating of your software, something you may be reluctant to do if the existing application does everything you need.

Converting Raw Files

In this section we will use Photoshop’s Adobe Camera Raw (ACR) because it’s our preferred raw file converter. ACR provides a wealth of adjustments; more in Photoshop than in Photoshop Elements, but even the adjustments available in Photoshop Elements exceed those provided by many proprietary converters.

We don’t have space for step-by-step instructions for using ACR. Instead, we’ll explain the key features provided in its workspace and how to use them when adjusting raw files. When you open a raw file, you’ll see a large preview window in the left side of the workspace, showing the entire image.

You can adjust the magnification of the preview by clicking on the + and – buttons in the lower left corner or with the Zoom tool at the left hand end of the top toolbar. This toolbar also contains tools for moving the image around in the preview window when zoomed in, sampling image colours to check white balance, cropping and straightening images, removing small blemishes, correcting red eyes in flash shots, masking out part of the image, applying a graduated filter and rotating the image in either direction. (Mouse over each icon to see what the tool does.)

Different photographers will use different tools from this collection. We’ve found the most useful tool to be the straightening tool as other adjustments are easier to carry out once the image is opened in Photoshop.

Most adjustments are carried out within the Basic Panel on the right side of the preview window. We’ll work our way down the list of sliders.

Temperature shows the color temperature of the White Balance setting used for the photograph. If the image colour isn’t correct, you can adjust the White Balance in one of four ways:

by moving the slider to make the image appear as you’d like it to;

by setting the numeric value to a specific value;

by clicking on a neutral toned area within the preview image using the eye dropper;

by choosing a standard value from the White Balance selector at the bottom left of the window.

The Basic Panel.

Tint allows you to fine tune the colour balance.

Below the Tint slider are two ‘hot’ buttons: Auto and Default. Clicking on the Auto button adjusts the image to what the software ‘thinks’ is should look like. The values in the sliders below change to reflect these adjustments. The Default button sets the values to zero, reflecting the values recorded by the camera.

In Photoshop there are nine parameters you can adjust with sliders.

Exposure sets the overall brightness of the image. Adjustments you make are reflected in the preview image and also in the histogram above the Basic Panel. If there’s a lot of black in the image, the histogram will have a large spike on the left side. Over-exposed images will show the histogram biased towards the right.

Use the Exposure slider to make sure that you have good tones throughout the image and that the blacks and whites are as accurate as possible. Triangles in the upper-left and upper-right corners of the histogram warn you when tones are ‘clipped’, which means details can no longer be recorded. Try to keep the graph between these indicators ““ but remember that if you’ve included a very bright area (like the sun) in the shot, no amount of image adjustment will get rid of the clipping warning.

The Contrast slider is centred by default. Moving it to the right will increase contrast in the middle tones of the image.

Moving it to the left can reduce tonal differences in the middle tones by making dark areas lighter and light areas darker.

The Highlights slider lets you darken very light areas and can help you to 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.

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 highlights, such as metallic surfaces, drag the slider to the right.

The Blacks slider adjusts black clipping in a similar fashion.

Below these sliders are three additional sliders for Clarity, Vibrance, and Saturation.

Clarity adds depth to an image by increasing local contrast. It has the greatest effect on the midtones.

Vibrance adjusts colour saturation (the intensity of colours) without going overboard and causing colours to be clipped. Colours with lower saturation are boosted more than highly-saturated colours, allowing skin tones to be enhanced without becoming unnatural looking.

Saturation adjusts the saturation of all image colours equally from -100 (monochrome) to +100 (double the saturation). This slider must be used very cautiously as excessive saturation produces lurid colours.

The link below the preview window allows you to set the output file format and bit depth for the processed image when it is opened in Photoshop. ACR lets 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 TIFF gives you the maximum amount of data to work with. This is the best option when you plan to make additional adjustments in Photoshop and it’s easy to reduce images to 8-bit after all processing is done if you want to save them as JPEGs for sending in emails or displaying on screens. Stick with 16-bit TIFF files for images that will be printed or archived.

DNG

Pentax and Leica are the only camera manufacturers to offer the ‘universal’ DNG (Digital Negative) raw format in their latest cameras. This file format was developed by Adobe and launched in September 2004. All Adobe software released since that time can open and convert DNG.RAW files,

A DNG file always contains the data for rendering an image without needing additional knowledge of the characteristics of the camera. There’s an option to include at least one JPEG preview to DNG files. These features ensure it is as ‘good’ as a proprietary raw format ““ but much cheaper and easier to use.

Although new versions of DNG are released periodically, full compatibility with older versions is maintained, enabling older versions of, say, Adobe Photoshop and Photoshop Elements to open DNG files from the latest digital cameras.

Also worth a look is RawTherapee which we reviewed in June 2013. It’s a powerful 64-bit open source raw converter for Windows, Mac OS X and Linux that is offered free under the GNU General Public License.

/ tips/shooting/JPEG-vs-RAW-Files for a comparison of both file types.

http://www.bythom.com/qadraw.htm   for a summary of what you need to know about raw files.

http://www.bythom.com/dng.htm  for a professional photographer’s commentary on the DNG raw file format.

http://www.luminous-landscape.com/ tutorials/bit-depth.shtml has an easy-to-understand tutorial on bit depth and its relevance to DSLR photography.

.

See Why shoot RAW? article.