Most new scanners today feature one-button scanning capability that is adequate for most projects. From time to time, though, you may encounter a poor or unusual original, something for which the automatic settings on your scanner cannot make proper adjustments. In such cases, it is good to become familiar with the controls available to fine-tune your scanner, in order to get the best possible outcome.
Calibrate your scanner and monitor
Before you do any scanning, it is essential to calibrate your scanner and monitor to ensure they are seeing and displaying colors correctly and consistently. Most scanner software includes a tool to help you perform this task, including HP's PrecisionScan software, which ships with many models of HP scanners.
Before you start, make sure your monitor has been turned on for at least half an hour to stabilize the display. The room lighting should be set to the level you will be using when you scan. The Calibration tool will present a dialog box and a pair of sample images: When the images match identically you will have completed the calibration. You may have to adjust the brightness and contrast controls on your monitor for correct settings.
Color correction
Color correction of an image usually involves adjustment to three different image qualities:
- Color balance refers to the comparative amounts of the three primary colors: red, green, and blue. Too much of any one color and your image will take on an unnatural cast (an effect you may wish to eliminate, or deliberately enhance).
- Saturation refers to the amount of white or black added to a pure hue to make it lighter or darker, respectively. A fully saturated hue has no neutral white or black components.
- Brightness and contrast refer to the relative lightness/darkness of each color and the number of different tones available. A high-contrast image is one with only a few tones of a particular color, ranging from very light to very dark, while a low-contrast image might have many tones clustered in the same range. Brightness tells us whether the available tones are clustered in the denser or lighter areas of the image.
If you are scanning at a high resolution (like 300 dpi), use your image editor, not your scanner software, to make adjustments to the color, saturation, and brightness of your scanned image.
The Color adjustments
Most scanner software, including HP's PrecisionScan Pro, includes the ability to make small color adjustments before scanning. The most common and easiest to use is the color tint wheel, a circle filled with the rainbow of available colors. Simply use the selection tool to choose the color you wish to emphasize.
For example, if your image has a yellowish cast, click on the opposite side of the center from yellow (blue) in order to make your adjustment. In most cases, you will also have a slider available to affect the saturation of the selected color, ranging from very light to very dark. Your changes should be viewable in the preview window.
The Exposer tool
HP's PrecisionScan Pro software includes a powerful tool for adjusting the brightness and contrast of an image. Click on Tools > Exposure Adjustments to open the Exposure Tool. In the window that appears, you will see the following controls:
- Midtones. Move the slider to the left (or click the down arrow) to decrease the overall brightness of an image. Move the slider to the right (or click the up arrow) to increase the brightness. This control adjusts the gamma value that defines the midrange of grays in the image.
- Highlights. Make the light parts of the image darker or brighter by moving the slider to the right or left or clicking the up or down arrows. To set a value for highlights in your image, select the white eyedropper and click the area you want to set as your whitest point. The highlight value will be set automatically.
- Shadows. Adjust the dark part of your images by moving the slider to the right to make them darker, or to the left to make them lighter. Or use the black eyedropper tool to select the darkest point in your image and set the shadow value automatically.
Adjustments to highlight and shadow can be seen in the movement of the red and magenta lines of the histogram, a graphical representation of the pixel distribution in your original image, displayed as a bar chart. The more "bunched up" the bars in the graph, the lower the overall contrast in your image.
Click Auto to return the Exposure Adjustments tool to optimal settings.
Other controls
A number of other controls can be used to adjust your image, either before or after scanning:
- Sharpening can help fix fuzzy originals by increasing the contrast between pixels at boundaries in image areas. There are limits to the effectiveness of this tool, and keep in mind that everything will be sharpened, including any dust or scratches on the image.
- Threshold is a level used by the scanner to determine whether a pixel will be represented as black or white, used primarily for scanning black and white line art.
- Luminance is related to saturation, but determines the amount of gray in a given hue, affecting the brightness or darkness of an image.
It is also important to consider the resolution you will use to scan the image and the file format you will use for the final output. You can learn more about resolution, bit depth, and file formats, along with more tips for getting the most from your scanner, in our article "How to scan."
|
Printable version
