Seven Steps To Scanning Success
Producing high quality scans is one of the most challenging elements of desktop publishing. In fact, most professional graphic designers and desktop publishers send out to a scanning service when precise colour and maximum quality are crucial. That said, it is possible to follow a few simple rules that help you produce good quality scans in most situations.
Know how your photo is going to be used and scan accordingly.
This encompasses, the final size, the resolution required for the type of printing you are using, and the best "mode" for the type of scan you are doing.
We will go through a couple of theoretical examples for the settings you need to choose in your scanner interface:
o In this example, let's start with a 4"x6" colour photo that we will be using in a b&w newsletter. First, set the "mode" to greyscale. In the newsletter, you will be printing the photo on the back page at an 8"x10" size. As this is approximately 200% of the original size, set the "scaling" in your scanning software to 200%. Having checked with your print shop, you know that the laser printed newsletter will be printed at 106 lpi (lines per inch), which means you need a scan of approximately 220 dpi (see chart below) to get maximum quality. If your scanning software allows it, you can set the scanning resolution to 220 dpi right away. Otherwise, scan at a higher resolution and downsample the "image size" to 220 in Photoshop to get your optimum resolution. NEVER "upsample" an image (unless you absolutely have to). This above example is also relevant to colour scans (simply set the mode to RGB).
o In this second example, we will be scanning a b&w logo that is made up mostly of text and b&w lines. You need to scan it for printing in an offset printed poster produced from linotronic output. To get the optimum resolution for this type of scan, it's usually best to scan it as "line art." Unlike greyscales or photos, line art scans must be scanned at much higher resolutions. In this case, because the project involves high resolution linotronic output, you will need to scan it at 1200 dpi. If you were printing from laser output, 600 dpi would likely be fine.
Approximate scanning resolutions
at 100% of final size:
(resolutions can be higher, although file size increases exponentially as resolution goes up)
Images for photocopying: 150dpi
Images for Colour Lasers: 180dpi
Images for digital printing or quick printing: 220dpi
Computer To Plate metal plate offset printing: 300dpi
Line art or text scans:
• 600dpi for laser output
• 1200 dpi for lino output
Halftone output resolution for images is usually measured in the printing industry in "lines per inch." A rough rule of thumb is that you need twice the dpi measurement in your scan should be twice the number of lines per inch that your project is being printed at. Lines per inch are not relevant to line art or text scans, so you generally want to scan your line art/text images at the dpi of the final output device you are printing to (ie. a 600 dpi scan of a line art logo will give you a great scan for a 600 dpi printer, 1200 dpi will work well for 1200 dpi and above output devices. It's hard to see any improvement when scanning at over 1200 dpi).
Keep your scanner glass clean and clean your photo before scanning it.
A dirty scanning surface can affect the colour and clarity of your scan. Also, it's amazing how much dust is attracted to photos. Wipe your photos with a soft cloth before scanning beforehand to save lots of touch up work later on.
Crop your photos individually when scanning to get the best "rough scan" you can.
Basically, make sure that you are scanning only the photo area (by cropping to the photo area, you avoid scanning a big portion of your scanner lid). Scanning software works much like an automatic light meter in a camera. It reads the "average" amount of light and creates what it thinks will be a pleasing result. This is why with a camera you will get a poor exposure if there is a large bright space or a large dark space in your photo. With the scanner, if you have a large white area from the scanner lid showing in your scan, it will also affect the "exposure." Also, at this point leave any fine-tuning in brightness and contrast until you have the image in your photo editing software.
Utilize a greyscale in your difficult scans.
By scanning a greyscale strip with your photos, you have a point of reference from which you can get almost "perfect" adjustments for brightness and contrast. If you have a "colour cast" in your photo, correcting your scan to match the greyscale will often fix it. While there are a lot of other steps taken by professionals, this approach will get you 90% of the way there. When correcting your image in Photoshop (or other image editing software), first go into the "levels" settings. In the levels settings, first match your midtone to the greyscale midtone (50% grey), match your highlight to the greyscale highlight (white), then match your shadow (black) to the greyscale shadow. This will not work perfectly in all circumstances, but should get you very close to the brightness and contrast of the original photo.
Please note that using a greyscale will not necessarily produce a noticeable difference when working with well balanced photos. It is when you have a unique or unbalanced image (ie. a photo of someone with bright backlighting) that this tool works extremely well. Greyscale strips are usually available through stores that specialize in graphic art supplies and often are supplied with your scanner.
Don't trust your monitor!
In adjusting for brightness and colour the worst thing you can do is blindly assume that your screen is giving you an accurate portrayal of how an image will print. Each monitor displays differently and each monitor can be adjusted for brightness and contrast - both of which are independent of the actual digital image! Learn how to read the "info" palette in your photo editing software for brightness and colour data and you will be well rewarded. Also, be aware that your colour inkjet printer is likely calibrated to print what the manufacturer considers "pleasing" colours, which may not be an accurate reflection of the digital data in your scan. In this case, you might work to get a nice quality inkjet print, only to be disappointed when the scan is printed professionally (and it looks nothing like your inkjet). A good idea is to get a proof printed from a reasonably accurate proofing device if colour is crucial to your job. A colour laser print from a well calibrated colour copier/printer is usually the most economical option for this type of proofing, although not as accurate as a dedicated proofing device.
Another challenge with your monitor is that it displays in RGB mode, while virtually any professional printing device prints in CMYK colour. You will typically want to change the "mode" for your colour scans to CMYK if the scan is destined for print. In doing this you will usually get a more accurate idea as to how the colours will print.
Learn some basic tools for photo editing in your photo editing software.
In this step, we will refer to Photoshop as it is the most widely used professional package. These tools also exist in most other professional packages.
While Photoshop (and most other modern applications) is infinitely powerful (and complicated), there are a few tools that are easy to learn that will pay big dividends in your images if you use them:
The clone tool: The clone tool samples areas from one area of your existing scan and paints them into other areas. When using the clone tool, you hold down the "alt" key, point the mouse and click in the area you want to "sample" from, then move the mouse and start "painting" the original area into another area. In addition to dramatic effects (as an experiment, try using this tool to give someone in a scan a third eye in the middle of their forehead) you can do for fun, the clone tool is indispensable for painting out dust spots, scratches, etc. When used with an appropriate sized soft brush, you can clean up just about anything. The biggest benefit for cleaning up images is that by using "pixels" or colours that already exist in your scan, the result looks far more natural that if you chose a colour to use in your cleanup.
Levels: In addition to setting the "input levels" for highlights, shadows & midtones, the "output levels" can also be used to vastly improve some scans. In cases where you have a scan with someone's face in the bright sunlight, there are usually "highlights" that are completely white. If you leave them this way, it will look like the subject has a "hole" in their face and will look extremely unnatural (particularly with b&w printing). The output levels have 255 steps from the shadow to the highlight. By dropping the highlight number from 255 to 230, you can generate a 10% screen in the lightest areas, looking much more natural. If you are doing high quality metal plate printing, you can get away with only dropping the highlight to 245 and thus achieving a 4% grey. Depending on the nature of the printing, there are different grey levels that will show up. For photocopying or digital b&w printing, you will often want higher minimum grey levels as these devices are not able to produce as subtle and light a grey.
Unsharp Mask: Utilizing the unsharp mask filter will let you sharpen many scans substantially and give you a much crisper looking scan- just don't oversharpen. A general rule of thumb is that when an image looks slightly too sharp on screen, it will print out just right. This is a tool that you will have to experiment with before being able to use it with confidence.
Save to the appropriate format.
If a scan is destined for use on your web page, by all means, save it as a .jpeg or .gif. If it is for use in print, save it in .tif or .eps format. These formats are universally accepted in professional operations (ie. newspapers, print shops, service bureaus). While it may be attractive to save something as a .jpeg because of the decreased file size, don't do it! This sort of compressed format may often result in lower printed quality, even if you can't see it on screen.
Those seeking further information may want to purchase "Real World Scanning and Halftones," 2nd Edition, by David Blatner, Glenn Fleishman & Steve Roth. This book is considered the "bible" of scanning by many in the graphics industry.
Hopefully this information has been clear and has increased your knowledge of scanning.
We strive to be as accurate and current with our information as possible. Due to the infinite number of scenarios that occur in print & desktop publishing, we can not guarantee that the above information will be correct in all situations.