correcting and enhancing digital photographs

This week will be looking at correcting digital photographs. By digital photographs, I mean files from digital cameras. There are several different types of file formats that can come from a digital camera. The most popular formats are, JPEG, TIFF, and Camera Raw. Adobe, recently, came out with a new file format, Adobe Digital Negative (DNG) that they are hoping will become an industry standard. Each one of these file formats has its own workflow and methods for correction and enhancement in Photoshop.

Most digital cameras perform some kind of adjustment when they record image data. That is, they will sharpen, adjust white balance, adjust exposure, make color corrections, adjust contrast, and who knows what else to your files. Camera Raw is a format that contains image data exactly how it was recorded. This gives you complete control over how the image is processed. Moreover, you can go back and make changes at anytime. If you shoot in camera raw and then archive your files to CD or DVD, you will create the closest thing to a negative in the digital realm. Most of you will probably never shoot in the raw format, but for those of us that are photo purists, raw is the only way to go. For more on Camera Raw: Why Shoot Raw.

The easiest way to open raw files is to double-click the file you want to open in Bridge. Bridge also previews the files, so you can see them before you open them. The Camera Raw dialog box contains the set of tools with which to process raw files. In the dialog box, you can perform a number of image adjustments without having Photoshop open. You can make these adjustments while Photoshop is processing other images in the background.

When adjusting white balance and exposure, the default settings are a great place to start. You camera records the white balance it has set at the time of exposure, Camera Raw reads this and displays it as the "As Shot" setting. Most of the time this works great. However, if the white balance is off, you can try using one of the presets or your can adjust the temperature (Kelvin color temperature) and tint manually. With the Calibrate tab, you can correct a shadow color cast.

By default, Auto Adjustments are turned on in Camera Raw. This means, tonal adjustments; exposure, shadows, brightness, and contrast are set automatically for you. Again, this is a great place to start. By dragging the sliders, you can make further adjustments. When making Exposure adjustments, hold down the Alt (PC)/CTRL (mac) key to make sure that you don't clip the highlights. When adjusting Shadows, hold down the Alt (PC)/CTRL (mac) key to make sure that you don't clip the shadows. While these tools are a good place to start, they do not offer the same control as levels or curves in Photoshop.

Many digital images contain "image noise" which are these random artifacts that degrade the image quality. They are usually the result of poor image sensors, high ISO settings, long exposures or underexposure. Luminance noise takes the form of dark, chunky patches or overall graininess. Color noise is usually visible as white, red and green dots. You can reduce image noise in Camera Raw in the Detail tab. Make sure to zoom in first to better view the change.

You can also apply sharpening in Camera Raw. This adjustment is very similar to the Unsharp Mask. However, since sharpening actually changes contrast, it should always be the last adjustment you make to an image. So if you think you will be making further adjustments in Photoshop, save the sharpening for later.

CS3 allows you to adjust jpg and tiff files in Camera Raw, however, similar tools are available directly in Photoshop for correcting and enhancing your digital photographs.

The first thing you should do is copy your files to CD or DVD to create a read-only archive. If you treasure your images, you will take this advise to heart. I can't tell you how many people I know that have lost images they did not archive. CDs and DVDs are cheap, its a wise investment.

The next piece of advise I'll give you is this, whenever possible, use an adjustment layer.

So, lets start with white balance. To tweak white balance in Photoshop, try using Photo Filters. Use the Photo Filters in an adjustment layer then once you choose a color and get the density right, you can adjust the opactity of the level for even finer adjustment. Also, make sure that you have Preserve Luminosity checked or your overall color saturation could be effected. If that doesn't work for you, use color balance, hue/saturation, or selective color.

Tonal adjustments in Photoshop can be made using an number of tools, the most useful being levels and curves. If you want to know more about levels, check out this article: The 1-2-3 of Photoshop Levels, for more about curves: Stealing Contrast with Photoshop Curves. The Shadow/Highlight command should be used with caution as it can lead to posterizaton and halos around the edges between shadows and highlights.

There is also a tool in Photoshop that can be used to reduce image noise. You can also apply this to JPEG files that have artifacts from too much compression. In this tool, luminance noise is reduced using the Strength slider and color noise using the Reduce Color Noise slider. You can also click on the advanced button to adjust individual color channels, when the basic is just not doing it for you. There will be times when no matter what you do you cannot get rid of noise, in that case, I will add more noise or grain. Using a texture filter, such as grain, will smooth out the noise and give the image an overall grainey look which sometimes solves the problem.

Vanishing Point lets you clone, paint and transform image objects while retaining visual perspective. You can also paste objects into an image to match a chosen visual perspective. This is useful when cloning an image with angled perspective when the clone tool doesn't work very well or to purposely distort objects in an image to match a visual perspective. You can add text to a car, a truck, a train, etc. and be able to match the perspective of that object.

With the Lens Correction filter, you can fix images that have barrel distortion (bulging created by wide-angle lenses), pincushion distortion (pinched in center caused by telephoto lenses), vignetting (dark corners caused by poor zoom lenses and teleconverters) and chromatic aberration (color fringing).

Our final image correction/enhancement is sharpening. As I said earlier, sharpening should be the last thing you do when working on an image. This is because sharpening doesn't actually sharpen the image, it only gives it the appearance of being sharper by increasing the edge contrast. This is a technique that is used in the darkroom and was then translated to Photoshop. The two tools that use this technique are the Unsharp Mask and Smart Sharpen. The other sharpening tools don't work nearly as well and should not be used. The Smart Sharpen tool takes the Unsharp Mask tool a step farther by adding 2 new algorithms (the mathmatical formula used to figure out which pixels should get what), Lens Blur and Motion Blur. Here is some good info on the Unsharp Mask: Behind the Unsharp Mask and on Smart Sharpening: Advanced Sharpening in Photoshop.