a short course in image scanning.. V2 this was mostly culled from emails and other communications with clients over the last few years, folks new to imaging, and particularly image scanning will find some useful information here.. okay, you've got a photo in your hand, but what you really want is to have that that image "on my mate's computer", or "on my web page", or *in my ftp folder*. The purpose of this short course is to guide you through the steps required to achieve that perfect scan. First we need a scanner. This is a very simple device which simply passes a photosensitive head over the image and converts what it sees into a stream of data.. ..the computer reads this data using the "TWAIN" interface (usually) and converts it into a viewable image. If it looks good, we can then save it to disk, copy it to the clipboard, whatever we want now that it's "in the computer". As a rule I always save my scans immediately. I use a wintel box for these kinds of jobs and crashing is always a possibility. USB scanners tend to be less problematic than their parallel counterparts, and SCSI devices (and now firewire) are the best of all. As a general rule, the faster the better, considering that some images can be very large indeed.. it's feckin HUGE!.. many people get a shock when they scan their first image. Knowing nothing of DPI, screen reselutions and other minor details, they hit "SCAN" and BANG! something the size of 16 monitors appears, or at least a small part of it appears. This isn't such a bad thing. As Ansel Adams said, "first you get the perfect negative". So long as your computer can take the pace (has sufficient memory and CPU power) this is a good strategy. Scan big, then reduce on the computer. That way you can keep the image quality high. Maybe you need to match the input resolution with the output resolution of your printer. For some uses, a quick low-resolution scan is all that may be needed. At some point we're going to have to know about all this DPI stuff so that we can make these kinds of informed decisions. DPI = Dots Per Inch, a measurement of "resolution" The bigger the DPI, the more dots (pixels) per inch and therefore, the bigger the picture. A good standard setting (and usually the default setting of an out-of-the-box scanner) is 300dpi. This is also the default for most printers, so if you scan an image and print it directly (without altering it in the middle) it should be the same size as the original. to intelligently decide what resolution to use, all we need to know is one thing.. WHAT IS THE IMAGE FOR? That's all that matters. We need to know the "target resolution", if you like. If the image is going on a web page, then a 72 dpi scan would probably be fine (though personally I'd use at least 150 dpi and reduce it later with Photoshop). If we are scanning artwork that is to be printed in a booklet, for instance, we would probably need to scan at 600 dpi, 1200, or even higher. Here are some typical resolutions. Computer screen: 72 (or 96) dpi standard home printer: 300 - 600 dpi high quality printer: 800 - 1600 dpi This explains why a 300 dpi scan looks so huge on the screen. If your screen is 800x600, that's 800 pixels (dots) wide. At 800 dpi a one inch scan would fill your entire screen! The exception to this might be where you are scanning for screen resolution (72 dpi), but have text in the original image that you want to be legible. In this case I would definitely scan bigger and reduce afterwards on the computer. The big "interpolated resolution" con.. NEVER scan an image at a dpi higher than your scanner's TRUE optical resolution. Simple. Many scanner manufacturers make wild claims about "interpolated resolutions" like 9400 dpi or 24000 dpi, but in reality the scanner is just rescaling the image itself. It might be argued that the scanner, being closer to the original, should be able to make a better job of this than some image editing software, but I've yet to see this. Most scanners are around 600dpi X 300dpi, check your manual. The big HOW-TO.. 1. Place the image face down on the scanner bed. Close the lid. 2. Fire up your favourite image software. For quick scans I use Irfan, or PSP7 if I have a batch to to. Any software that supports the TWAIN interface will be able to capture scan and make sense of it. Often TWAIN capability is built into word- processors, OCR packages, DTP software, so check that first, then you can miss out the middle-man, so to speak. 3. Chose "acquire" from the menu.. it's usually under the file menu somewhere, maybe in a twain sub-menu. in Irfan it's CTRL-A. The scanner TWAIN application will appear. If this is your first scan there will likely be a short delay while the scanner warms up. If these seems archaic, the he reason is that the scan head needs to reach a certain "colour temperature" before it makes the scan. If the scanner app didn't appear, you probably haven't told the computer what your preferred device is. Just chose "select Twain source" or something along those lines from the menu, and chose your scanner from the list. 4. Do a Preview scan. this allows you to see what the scanner will see. It's just a quick, very low resolution scan. Now you can set the cropping, colour, brightness, etc. usually leaving everything "in the middle" is the best strategy, altering such things with your imaging software. 5. Click "SCAN" if all goes well, the scanner will burst into life and begin the scan operation. after a wee while (depending on how fast your scanner, and it's interface is) In a few moments your image will appear in you imaging software's window as a new file. 6. Chose "save" or "save as" from the file menu. Give your image a meaningful name, and save it. You may want to work some more on the image, rotating, scaling and altering it, etc, but now you can always go back to the saved image if you make any mistakes. ** I'm going to butt-in here with a quick note about image formats.. It's still REALLY feckin HUGE!! You may have noticed that your saved image is still enormous. If you intend to send this over any networks (like the internet for instance) obviously this size thing is going to be a problem. We need to somehow compress the file. I guess we could zip it (or RAR it) but that probably wouldn't make much of a dent in the file-size; these types of compression schemes just weren't designed for pictures (although the multimedia scheme of WinRAR does a commendable job) Fortunately there is a much better way. bitmaps and un-bitmaps.. When you save the image in your imaging software (Irfan, Photoshop, PSP, etc) you will be given a choice of "image formats". Entire volumes have been written about image storage schemes, but with the topic firmly in hand I'll say there are basically two types. The first and most basic is a bitmap. Bitmap images are just that, a map of all the bits, or dots (pixels) of the image. A bitmap is an exact record of the exact value of each and every pixel of the entire image. Bitmaps can get very large indeed. Some common bitmap formats are: BMP, TIFF, PICT and XBM. Most bitmap formats have introduced compression schemes of some sort to try and save space, and some do a fair job too. if you need an "exact" reproduction than you must use a bitmap format. "smart" image formats.. Most people don't *need* bitmaps. The kind of person who needs to use bitmaps probably wouldn't need to read this (unless it was just for fun). The ubiquitous JPEG is just fine for most images, because most images are *photographic*. Jpeg compression is specifically designed for photographic images and the compression algorhythm is designed around what the human eye will see. It's very clever indeed, and if you're interested in the nuts and bolts of the format, the jpeg group produce an excellent FAQ on the subject. Jpeg compression can be ridiculously high. I've seen 10MB files reduced down to 50k!! But, as always, there is a trade-off. Here it's a question of quality. Simply put, the more you compress an image, the more you degrade it. A JPEG with a 50% compression will be *tiny* compared to the original, but will be noticeably degraded. Small text will be probably be illegible, a "blocky" effect will be in evidence. But even at 10% compression (90% quality setting) the file will be significantly smaller and an expert would probably find it hard to tell the difference. Usually a setting of 75-85% will do just fine, sliding up and down depending on the target audience. There are many other compression image file-types too, the most famous being the GIF, which is a proprietary format, owned by CompuServe. JPEG is a lossy format. This is important. You must remember that every time an image is saved in JPEG format, some quality is lost. If you save a *perfect* image as an 80% jpeg, it will still look fine. But if the resultant image is opened, and then saved again (maybe for a crop or something) then *more* quality is lost. Do this ten times and the image will be tatties! A bitmap would, of course, be perfect every time. Ideally Jpegs are saved only once, for transit, from the original bitmaps. *very* smart image formats.. There are some newer formats that seem to achieve the best of both worlds, like the Lura-Wave format with extremely high "lossless" compression, but these are mostly proprietary formats, and licensing issues will always cause distribution problems for some time to come. So, to the rescue comes.. THE MIGHTY PNG! This is a modern, FREE format, which achieves superb compression ratios with lossless quality, handles greyscale, full colour, transparencies and much more. It works better on some images than others and a little experimentation is required to find the best settings for the kinds of images that you work with. It works extremely well with non-photo data, like desktop screenshots, logos, graphics, etc. this is now my most common used image format. As a rule of the thumb.. for photographic scans, save as a JPEG at about 85-90% quality (10-15% compression) unless you have a good reason not to. One final note about jpegs: HUGE images don't compress as well as smaller ones. (it's illusion really, or rather "perception", so therefore, quite real!) Also highly detailed images can foil the JPEG algorhythms. Allow me to illustrate.. I have an image 2048 X 1024 pixels, 24bit colour. It's a desktop screenshot of my system, pasted 6 times over. It's huge. As an uncompressed bitmap image it takes up 8MB of space. As an 80% jpeg it takes up 445k. The jpeg is a little fuzzy around the text and borders though still legible. Messy, but readable. Saved as a mighty png it takes up 265k!! that's a mere 1/30th of the size! and, the png is identical to the original! With desktop screenshots and similar detail the PNG is obviously the format of choice being small and also perfect. A photograph, on the other hand, would tell a very different story. Here the jpeg would almost certainly be smaller. A quick 1024x768 experiment produced a jpeg of 198k, compared to a PNG of over 1MB. They look the same. For photographs, the jpeg is king. Quite often the imaging software will have a jpeg optimiser which allows you to set the SIZE you want and let the software work out what compression you will need to hit your target. For peecee users, PSP (PaintShop Pro) has one built in, and Photoshop (most platforms) has a number of third-party plug-ins that do a fine job. The built in PSP optimiser very usable, gives a readout of the projected file size and also a preview of the resulting image live, as you move the compression slider up and down. It will even calculate the download times for you! Superb. ImageReady (which comes with photoshop) does all these things too; and as psp isn't available for mac, my weapon of choice for working with images for web. well, that's it! hope this help you take better scans.