Wednesday, February 17, 2010


Fixing Sunny Day Shadows and Color Casts with Corel PHOTO-PAINT®

By Steve Bain
Whether you're a professional, a tourist or just a weekend photo hobbyist, there's nothing like taking a few pictures in the great outdoors. Sometimes, though, that sunshine you enjoy can hamper your photographic efforts. The bright light and harsh shadows may hide the person, place, or thing you specifically want to capture.
The problem is often due to incorrect exposure caused by your camera's automated features and extreme light levels entering the lens. The internal light meter averages the values of the light and dark areas you see through the lens, and your camera's internal program uses these values to set the exposure for the complete scene. Sunlight skews the averaging, causing underexposure. You can correct this unwelcome side effect of a sunny day in several ways. Whether you are using a digital camera or scanning your photos, Corel PHOTO-PAINT® allows you to correct lighting problems after your image enters the digital realm.
Because it's often too difficult or time-consuming to restage what you originally photographed, the trick is in knowing how to correct the digital version. Different situations require different correction methods, depending on the intensity of the light source, or sources, in your photo and on the location of shadowed areas. Isolated bright spots can cause overall darkness in an image. On the flip side, a brightly lit scene can include isolated shadows in unfortunate places, such as under the brim of a hat or in the spot where a subject is standing. Corel PHOTO-PAINT offers several methods to coax hidden details from the shadows.
Salvaging Dull Pictures
When bright light reflects off surfaces like snow or water, it can create highlights intense enough to cause the rest of the image to appear dull. One strategy for lightening the image is to use one of the adjustment filters in Corel PHOTO-PAINT. You can control the sliders in the Brightness/Contrast/Intensity dialog (see below), which you open by choosing Image > Adjust > Brightness/Contrast/Intensity, or by using the Ctrl+B shortcut.
The Brightness, Contrast, and Intensity sliders enable you to adjust these properties as percentages of the original values. In the water scene below, light from the bright sparkles created by sunlight reflections has caused underexposure of the main subject. With all three sliders in the dialog set at 40 percent, the areas of shadow in the previously dull image become more detailed, and the overall image is improved.
Depending on the contrast qualities of your image, you can also play with gamma and contrast to reveal shadowy areas. Options in the Contrast Enhancement dialog (see below) enable you to adjust the gamma range of an image while adjusting the input contrast settings. To access this feature, choose Image > Adjust > Contrast Enhancement.
The tools in the dialog enable you to set the input and output ranges for the black and white limits of your image, or adjust the image's gamma range, or both. Slightly reducing the upper limit of the Input Value Clipping range can lighten the overall image, including the shadowy areas. In the example below, light reflections are enough to cause overexposure of the entire image - including the main point of interest. In this case, reducing the input clipping value of 255 (the default) by half was enough to bring the shadowy details into view.
Lightening Shadows with the Effect Tool
If your shadows are simply isolated instances, applying an adjustment filter to the entire image may correct the shadows, but it may ruin the lighting in the rest of the image. Here's where you need a strategy with a little more finesse to correct the image. The Effect Tool in Corel PHOTO-PAINT includes two brushes that are perfect for lightening shadowy areas interactively: Brighten and Dodge/Burn.
To access these effect brushes, choose the Effect Tool (V) from the Toolbox, click the Effect Brush selector in the Property Bar and choose either Brightness or Dodge/Burn (see below).
Brighten Brush
Brighten is the default brush type for the Effect Tool's Brightness brush and enables you to brighten certain areas of an image interactively. You can also choose one of seven other preset brush types that vary in nib shape and size (see below). To correct image shadows, you'll need to use a brush with a soft feathered shape at a size which roughly fits your shadow area. The Shape and Size options offer further control.
To apply the Brighten brush and lighten a shadow, follow these steps:
  1. With the Brighten brush selected, set your nib size and shape options. Large, feathered Brighten brushes are best for subtle corrections. If you find that the effect is too weak or too strong, click the Open Advanced Options button on the Property Bar (see below), and use the Amount and Transparency options to make adjustments. Lower positive Amount values and higher Transparency values apply less brightening. Test your settings before proceeding, and use the Undo command if you need to reverse the action.
  1. To apply the effect, drag over the shadowy area that you want to brighten. You'll find that the effect is cumulative - each time you apply the brush, the shadowy area becomes brighter.

  2. Each stroke you apply with the Brighten brush is a separate command. This means that if you applied the brush strokes in short sessions, you can roll back your brightening effect in steps by using the Undo command. Be sure to avoid brightening your shadows beyond what appears natural to you. When a shadow has been brightened and the changes to the image have been saved, the changes to the image's pixels become permanent.
In the example below, two-thirds of the image shows the shadowy side of a building while the blue sky and other elements are properly exposed. The Brighten brush was applied with a large nib size and a soft feathered nib shape. Amount was set at 5, and Transparency was set at 50.
Dodge/Burn Brush
The Dodge/Burn brush is a shadow-correcting tool that enables you to brighten areas selectively based on their tone. The brush actions are fashioned after the darkroom methods used to expose film negatives onto photographic print paper. When an exposed area is dodged, less of the image is exposed onto the print paper, making the area appear lighter. Burning has the opposite effect: exposing certain areas longer makes them appear darker.
When the Dodge/Burn brush is selected from the Effect Tool selector, you can choose from three Dodge brush types, which enable you to dodge highlight, midtone, or shadow areas (see below). Like the Brighten brush, this brush effect also comes with options to set the nib shape and size, and set specific values for the effect's amount and transparency.
To dodge the shadows by using the Dodge/Burn brush, follow these steps:
  1. With the Dodge/Burn brush selected, pick a shadow area to dodge, and choose a suitable brush type from the selector on the property bar. Because you're correcting shadows, you'll most likely be using the Dodge Midtones or Dodge Shadows brush type. Shadow tones vary according to the brightness, contrast, and intensity of your image. Your brush type selection is limited, so use your best judgment as to which type will work best.

  2. To avoid the effect of hard brushed edges, choose a soft (feathered) nib shape and a size that roughly matches the pixel area you're correcting. A large brush size allows you to apply the effect to the entire shadowy area in the least number of strokes.

  3. Select a shadowy area that is well defined in contrast to the surrounding image elements. Test your settings by dragging over the area to apply the Dodge effect. Adjust the Amount and Transparency values to control the intensity of the dodge effect. Aim for less effect instead of more, and use multiple brush stroke commands to increase the effect in steps.

  4. With your settings adjusted, apply the brush over the shadowy area. The Dodge brush enables you to adjust specific shades of areas, so you can straddle areas where the adjacent colors are in sharp contrast to the area you're dodging.
In the example below, the Dodge/Burn brush was used to lighten the shadows covering more than half of a city street scene. The sunny area of the image was left unchanged, whereas the portion shrouded in shadow was lightened with the Dodge/Burn brush set to the Dodge Midtones brush type. A soft feathered nib shape set to a large size was applied with an Amount value of 50 and a Transparency setting of 20.
Tips for Effect Brushes
The Effect Tool in Corel PHOTO-PAINT can be incredibly handy if you're an experienced user. But if you don't yet have practical experience using them, here are a few tricks you can use to as you perfect your technique.
Use a Pen Tablet - When applying brush strokes, you can maximize your stroke efforts by using a pen tablet. A pen tablet is a much more intuitive device than a mouse and offers you better control over the direction and accuracy of your brush strokes. If you have one, use it. If you don't, then consider purchasing one. Pen tablets have come way down in price, and there has never been a better time to take the plunge.
Limit Your Brush Strokes - Effect brushes apply changes cumulatively, meaning the effect is amplified each time the brush is applied. This means that during a single brush stroke session, the effect is applied uniformly to the brushed area so long as your pointing device button is pressed.
Bigger Is Better - When retouching or correcting shadows, use brush sizes that are as large as possible, so that you can apply the effect to large areas quickly and in a single brush session.
Effects and Files - The Undo (Ctrl+Z) and Redo (Ctrl+Shift+Z) commands are invaluable for reversing the occasional mistake made while using a brush effect. On the other hand, if you want to keep the effects you're applying, be sure to use the Save As command to make your current and corrected image a separate document file.
Positive vs. Negative Values - The property bar includes an Amount control, which enables you to adjust the strength of the effect you're brushing onto your image. When you enter positive Amount values, the effect is applied normally. Just keep in mind that if you enter a negative value, the opposite effect results. In the case of the Brighten or Dodge brushes, negative values would apply darkening and burning effects, respectively.
Correcting Shadow Color Casts
One of the drawbacks of taking photos outdoors is that a color cast often appears throughout your picture. Although color casts come in many different hues and shades, the most common is caused by a clear blue sky. The blue cast this causes alters even the true appearance of other colors in your photo, which makes this side effect particularly nasty.
The Selective Color filter in Corel PHOTO-PAINT can help you solve this problem. Options in this filter dialog (see below) enable you to adjust the CMYK (cyan, magenta, yellow, black) color values of specific colors individually in your image - even if your image is in the RGB (red, green, blue) color space.
A typical blue cast is often composed of various shades of blue. In color terms, sky blue is composed of cyan and magenta. The Selective Color filter enables you to change specific CMYK values of blue or cyan, or both, so these are the two colors you'll need to adjust. The adjustment values are based on percentages ranging from -100 to 100 percent. Negative values decrease a specific color, whereas positive values increase it.
To correct the blue color cast in an image, follow these steps:
  1. With your image open, choose Image > Adjust > Selective Color to open the Selective Color dialog.

  2. In the Color Spectrum area, click the Blues radio button. In the Adjust area, move the Cyan slider to the left until the blue cast begins to fade and the colors appear pinkish. Now, slide the Magenta slider to the left an equal amount (see below), so that the blue fades dramatically.
  1. If the blue cast persists, you may need to reduce the cyan color values also. Click the Cyans radio button in the Color Spectrum area, and move the Cyan slider to the left until the remaining blue cast disappears (see below).
  1. Click OK to apply the change and close the dialog.
Because the Selective Color filter enables you to adjust the color values of specific colors, you have total control in challenges of color correction, such as when you need to remove color casts without affecting other colors. In the example below, the midday blue of the sky has made the wheels of this locomotive turn blue. In the corrected version, the Cyan and Magenta values in the Blues color spectrum are both set to -100, and the Cyan value of the Cyan spectrum are set to -50.
We've covered the various ways you can reveal hidden details from harsh shadows, and we've dabbled a little with correcting color casts. The next time you head out with your camera on a bright sunny day, you can snap with confidence, knowing that Corel PHOTO-PAINT can help you clean the mess the sun left behind.
Steve Bain is an award-winning illustrator and designer, and the author of nearly a dozen books, including CorelDRAW: The Official Guide.

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