Have you ever compared a scanned image with the original source? You’ll notice that the scanned image is never as accurate as the source with regard to details like sharpness, color, contrast, brightness, saturation and so on. The results will be close to accurate only if you have a high-end scanner which is properly color-calibrated. However, for most of us who own neither a multifunctional device nor a conventional flatbed scanner, getting accurate results is a distant dream.
The accuracy of a scanner depends on the quality of its CCD sensor and the lamp present on the carriage assembly. The better the CCD sensor, the more details it can register and hence, higher the output quality. Other than the scanner itself, the output also depends on the post processing done by the imaging application that comes bundled with the scanner. Since, most of the factors that determine the output quality cannot be controlled, you have no other option but to save the scanned image as it is. If you haven’t yet bothered to check the difference between the scan result and the source try this—scan a photograph and compare the scanned image with the actual photograph and note the difference.
The most visible difference will be a slight loss of sharpness and mismatch in color levels, brightness and contrast. In some cases you will even notice the presence of noise in the scanned image.
The only way to correct scanned images is using a power imaging application like Adobe Photoshop. You can eliminate noise, sharpen the details, manipulate color levels, adjust the brightness and contrast and do much more to bring your scanned images nearer to the original.
The reason that most people hesitate to correct scanned images is because they feel that Photoshop is tough to use or they’re afraid they might do more damage. But in reality, it’s very simple. You don’t have to be a wizard at Photoshop. It takes just a few minutes to correct an image. This workshop will guide you through the entire process of correcting scanned images from scratch and achieving the best results.
If your scanned image is tilted, first
rectify the tilt:
· Right-click on the image and select “Fit on Screen” after selecting the Zoom tool from the Tools sidebar.
· Keep pressing “Shift+i” until the Eyedropper tool located above the Zoom tool changes to Measure tool.
· Now, drag a line across the border of the scanned image and select “Image | Rotate canvas | Arbitrary”.
· Click on “OK” to rectify the tilt.
After fixing the tilt, crop the required area using the Crop tool from the Tools sidebar. The actual image correction process starts now. In the first stage, get rid of the noise in the scanned image.
· Go to “Filter | Noise” and select the “Dust and scratches” filter
· Set the Radius to 1 pixel keeping the Threshold to 0 level.
· You can check and uncheck the “Preview” option to view the effect.
· Click on “OK” to apply the filter.
The “Dust and scratches” filter gets rid of most of the noise. However, if you take a closer look at the image, you’ll still see a little bit of noise. To get rid of this, use the Gaussian Blur filter.
· Go to “Filter | Blur” and select
“Gaussian Blur”.
· Set the radius between 0.3 to 0.5 pixels. Check and uncheck the “Preview” option to notice the effect of the plug-in. Keep the radius low or else it may affect image details.
Applying the Gaussian Blur results in a slight loss of details. To compensate for this, you need to sharpen the image.
· Go to “Filter | Sharpen” and select the “Unsharp mask” filter.
· In the filter’s dialog box, set the radius to 2 or 4 pixels with the threshold set to 0.
· Now drag the amount slider to 25 percent and note the difference using the “Preview” option. The value should be between 25 to 30 percent.
If you have Photoshop CS2 installed, you can go a step further and use the “Surface blur” filter. This filter is useful for further eliminating noise and graininess. It uses the blur effect while preserving the sharpness of the edges.
· Go to “Filter | Blur” and select “Surface blur”.
· Set the radius to 1 pixel and set the threshold value to 27.
· If you aren’t satisfied, you can further increase the threshold by 3 to 5 levels.
Finally, it’s the overall tone of the image which has to be corrected. The easiest way to correct the colors is by using the “Auto contrast” feature. To do this go to “Image | Adjustments” and select “Auto contrast” or simply use the keyboard shortcut “Alt+Shift+Ctrl+L”. You’ll immediately notice the increase in vibrance. If you’re familiar with Adobe Photoshop you can even try adjusting the color levels manually.
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