Better scanning
There’s no question about it, having a scanner to play around with is good fun. While most scanners now include software with a range of different settings to make scanning easier, getting your scans to appear ‘just right’ can be a frustrating experience. For example, if you’ve ever attempted to scan copy from a magazine or newspaper, you’ll have no doubt run into the annoying dot pattern these scans seem to produce every time.
While the default or basic settings can help, getting into the advanced settings of your software or image editing application can make a world of difference. This month, we look at some simple but effective techniques that will help to improve the quality of your scans.
Moiré patterns
Unlike a traditional photograph, images and text found in magazines and newspapers are printed using a half-tone pattern. While this isn’t generally discernable to the human eye under normal reading conditions, look closely and you’ll notice that the image is made up of a dot-like or crosshatch pattern. Unfortunately, this is most evident when you scan either of the above as traditional colour or greyscale photographs as it compromises the quality of the scan. this is normally referred to as a moiré pattern.
The great news is that while moiré patterns represent a serious obstacle, most scanning software includes a simple and effective filter to tackle the problem. Known as a descreen filter, it’s often implemented as a checkbox or simple drop-down menu option in the advanced settings of the scanning software. There may even be an option in your scanning software to scan from a magazine, and this will automatically implement the descreen filter for you. While scanning an image using the descreen option will take longer, the results speak for themselves.
In some cases, using the descreen filter alone won’t completely remove the crosshatch or dotted pattern to a degree that you’re satisfied with. If you find this to be the case, check out some of the tips in this article.
Actuality
When attempting to determine the quality of a scanned image, you should always view it at its actual size. After scanning any image into your image editing application, that image will almost always appear in a mode that attempts to fit the entire image into the screen area. Unfortunately, this preview can be misleading since the smaller size makes it hard to judge the impact of issues like moiré patterns.
To gain a truer sense of the quality of a scan, it’s imperative that you view the scanned image at its actual size. Simply use the settings found on the program menu, or by right-clicking with the magnifying glass tool selected. At the actual size you’ll get a much better representation of the scan’s quality.
Blurring and sharpening
Image editing applications such as Adobe Photoshop include a variety of different filters than can be applied to help improve the quality of any image, including scanned ones. One popular technique to help minimise the impact of issues such as moiré patterns is to scan the image at double the resolution required, with the descreen filter on. You then resize the image to half the size and apply a filter known as the Unsharp Mask. Although its name might not suggest it, the Unsharp Mask is a filter used to restore the sharpness in an image, some of which may be lost after sampling an image to a smaller size.
Addition by subtraction
As outlined in the previous section, resizing (or resampling) an image to a smaller size can be an effective way to help improve the perceived quality of a scanned image, especially when combined with different filtering techniques such as blurring. To get the greatest benefit from the technique, make a point of scanning images at a higher resolution than you need, applying filters to help improve the quality of the scan and then resampling the image to a smaller size. Always try applying the Unsharp Filter on the reduced image to see whether the quality improves.
Almost all image editing applications enable you to preserve the ratios associated with your images or specify a new size percentage. The Image Size dialog in Photoshop provides this in various measurements, along with resolution information.
When trying to determine the most appropriate resolution for your image, always keep your intended destination in mind. For example, if you’re using scanned images for the web or on-screen displays, you don’t need 300dpi resolution – something around 75 or 100dpi will suit your needs. If you’re planning to reprint or enlarge your scans, you’ll definitely need a higher resolution, typically in line with what the output printer will support. Viewing an image at its actual size or using the print preview function will give you a better sense of whether your current resolution is too high, low or just right.
Going greyscale
Most scanning software packages include a greyscale colour mode for scanning black and white images, whether from photographs, newspapers or magazines. Just as colour images from magazines and newspapers are impacted by moiré patterns, so are non-colour images, so be sure to use the descreen filter. Although most black and white images should be scanned in greyscale for the best results, certain exceptions apply. For example, many old photographs might use a sepia or brownish tone rather than true greys, so scan in colour to maintain this consistency.
For cases where you want to convert a colour image to greyscale, scan the image in colour and then convert it to greyscale later using your image editing application. This will give you a greater degree of control with the filters you can apply to the image, and all image editing applications include the ability to convert images to greyscale. Having your master copies of scans in colour will ultimately give you more flexibility in the future too.
Photo imperfections
One common issue encountered when scanning images is imperfections on the original image. Many programs include filters to compensate for this problem, which is often referred to as noise. Examples include speckles that appear randomly, dust marks or scratches on an original. If these imperfections aren’t overwhelming, noise filters can solve the problem. Photoshop includes a variety of these, such as the Dust and Scratches, Despeckle and Median filters. In cases where a scan still doesn’t seem true to form, try applying these filters individually.
Attack of the clones
While filters may help with minor imperfections in images, larger or more serious ones must be corrected manually, especially in the case of older, creased photos. In these cases, you’ll need to open the scan in your image editing application and use the Clone tool, if one is available. This tool often appears as a rubber stamp icon and it enables you to copy small bits of a surrounding area and then use that ‘image’ as filler for the damaged areas.
To get the best results with this tool, enlarge the image to many times its original size before trying to clone areas. This gives you a larger and more precise working space, and any minor touch-ups are unlikely to be visible once the image size is reduced again.
Judgement time
Whether you’re scanning photographs, copy from printed sources or just plain text, your own eyes are the best judge of quality. Choosing the correct type of scan in your scanning software is obviously the most critical initial consideration, but it’s far from the only one, especially if you’ve got a decent image editing application on your PC.
Play around with the various advanced settings of your scanner software in Preview mode, and when you have a preview that looks right to you, scan your image. If it’s still not perfect, don’t fret – try out some of the different filters outlined in the article until you find the settings that best meet your needs. With a little bit of trial and error, better scanning results are well within your reach.
Keep it clean
Sometimes the most important tips are also the most basic. In this case, make sure you keep the surface of your scanner’s glass clean. Over time, this surface gets messy and while it may not have the most noticeable impact on your photos, it can certainly have enough of one to require additional and time-consuming touch-ups later.
One obvious tip is to always keep the scanner’s lid closed when it isn’t in use. When the glass does need to be cleaned, your best bet is to use a mild glass cleaner, although some manufacturers recommend pure alcohol or a soap and water solution. Regardless, never pour or spray the solution onto the glass. Instead, wet a lint-free cloth with the solution and wipe the glass gently. Most importantly, be sure to completely unplug the unit prior to cleaning, and give it time to dry before plugging it back in.