Sansoft LLC Scanner Tips

Are you not getting enough out of your scanner ?

Scanners and Digital Imaging

The first lesson in scanning. You need to determine what device you will be sending the scanned image to. If it is just the display monitor, it makes it much easier. Just think of the resolution that your monitor is set to. Most people have it set to 800x600 which means that there are 800 pixels from one end of the screen to the other. On a 15 inch monitor, you actually have about 11 inches of Horizontal screen image. Divide the 800 pixels by 11 inches and you get an effective screen resolution of 72 dots per inch. On the same monitor set to 1024x768, the dots per inch calculate out to 93. If you are keeping up, then you realize that to scan for displaying on a monitor, you only need to scan at around 90 dpi. With this revelation in mind, a simple 300 dpi scanner works great when using a program like Jasc's Paint Shop Pro to directly scan in an image and resize it for the screen.

A few of words of caution. This works great if you are planning to use the image at the same size that you scanned it in or less. Where you get into trouble is when you want to enlarge the image because you start loosing resolution if you just say double the size of the image. For example, say you have a standard 3x5 snapshot that you want to display as a full screen image but don't want to loose resolution in the process. Since you know that your screen has 800 pixels across, you need to boost the scan resolution to 160dpi. I calculated that by taking my 800 pixels and dividing it by the 5 inch size. But what if my image was only one inch in size. Then I would need to scan it at 800dpi.

Struck with this bit of knowledge, I then started to look at what it really takes to print out an image. Here things get tougher as the printer manufacturers will tout their super high printer resolutions but never give you much advise on how to take advantage of it.

The printing world never used to talk about dots per inch. They are more concerned with line screen frequency (lsf) because in the days of printing presses, they would work in lines per vertical inch. Unfortunately, I have yet to find a very good web site on the subject and if someone has, please let me know. So how do we convert from lsf to dpi? The first stop is with the printer manufacturer. According to HP, the 600 dpi laser jet printers have an output of 85 lsf. According to Epson on their ink jet printers, you calculate the lsf by the following formula. Take the rated dpi of the printer and divide by 6. My Epson Stylus Color 800 is a 1440 dpi printer and so according to the formula, the lsf is 240. To convert the lsf to dpi, multiply it by a factor of 1.5 to 2.0. (Don't ask me why one or the other.)

The trick here is to scan for the capability of the printer. According to the calculations above, a 360dpi Epson ink jet printer should have the image scanned at 90 dpi. My 1440 printer should have the images scanned at 360 dpi and the Laser Jet 600 dpi printer should have images scanned at around 130dpi.

Now all of the above regarding printing refers to scanned images like photographs and the like. There are a couple of special issues and I will cover them briefly here. One is line art where you need to scan in an image that will be rendered or used with a vector graphics program. These need to have all the dots connected in a line that is scanned in so for this type of work, you must scan in at the highest resolution you can. The other situation is scanning for fax output or OCR (Optical Character Recognition) work. Fax systems usually scan at no more than 200 dpi. OCR text sometimes needs a bit higher resolution to make sure that you capture all the "ink" on the paper in the letters and numbers.

So now you have an idea as to the minimum scanned resolution you should be using to scan in pictures for printing. Again, this is if you will be printing at the same or a reduced size as the original image scanned in. As with the conversation regarding scanning for the monitor, you need to think about how large an image you want to print relative to the original size. On my Epson 800 printer, I came up with a scanned dpi of 360. But what if I want to turn my snapshot into an 8x10 print ? Well, by doing the math (and measuring), I see that my snapshot is actually 4 inches by 5.75 inches in size. For this, I would actually just double the size to be printed but to keep the resolution I need to print it, I would also have to scan it at 720dpi. What you have to watch out for is if you decide that you only want a smaller section of the image. Or even worse, say you want to scan in a 35mm film slide that is only 1.375 by .875 inches in size. To print it out full size on an 8.5x11 paper takes an 8 times increase in size, or for my Epson printer, I would need 2880 dpi. Again, it gets worse if you want to crop the image in the slide.

So you can see that a cheap 300 dpi scanner is just not going to do the trick when you want to significantly enlarge the picture. Not only that, It doesn't have the capability to scan in negatives or slides not that it would do me much good if I could. In looking around at scanners, I now see that resolution matters a good deal depending on how large you want to scan the images.

So What Scanner Do You Choose ?

There are quite a few scanners out on the market with a range of features to make a veteran used car buyer go nuts. For this discussion, I will ignore the page type and the small hand held scanners as well as the large volume document scanners as we are trying to figure out what to do for photos and prints and negatives and slides.

From the discussion above, you need to answer a few questions.

First question: Besides prints, Do you only have 35mm slides or negatives to scan? In other words, no other negative film sizes such as the 6x6mm medium format cameras.

2nd question: how large of a print do you want to make out of your slides?? (Very important). This makes a big difference as expanding a 35mm slide to fill an 8.5x11 page is expanding the print size 8 times. Worse if you crop.

3rd question: how large of a print to you want to make from 4x5.5 prints? Here, to go to 8 x 10 inches is just doubling the size which means we don't need that much of resolution scanned.

4th question: do you want the same scanner to be able to handle both film, slides, negatives, and prints? You might need to get two scanners depending on how high a quality image you want out of each format, print and slide/negative.

5th Question: what kind of printer will you be printing these images on and what is the resolution? The higher the resolution of the output printer, the higher you need to scan at.

6th question: How much money do you want to spend for all of this?

Choosing the Scanner

So, what scanner to get? For web based printing or just displaying your images on the monitor, at the most, you need only about 720 dpi even if you want to take a slide and blow it up to cover the entire screen at 800x600. If you don't need to deal with slides or negatives, go with a scanner like the Umax Astra 2000 series at around $149. If you need the 35mm slides and negatives, go with Microtek Scanmaker 4 or Agfa Duoscan 1200T at around $699. Any higher resolution out of the scanner kicks you up to the $2500 range.

For scanning prints, slides, and negatives for printing on a high resolution ink jet printer the price goes up quite a bit. Here you go to the class of the Agfa Duoscan Solo or the Microtek Scanmaker 5, both are a 1000x2000 scanner at $2500 and they still don't scan as high as I would like. The advantage to these scanners is that they actually have two light beds. One for holding the normal print images, and the second tray or drawer for slides and a variety of negatives.

The alternative here is to get two scanners. One a standard flatbed type, and the second, a film scanner. These are specialized high dpi scanners just for film slides and negatives. They come in a variety of sizes and in fact, some of the new ones now accommodate the new APF film canisters found in the new 35mm cameras. Some will also handle larger negative sizes. A few worth looking at start with the HP Photosmart. 35mm only, it is a 2400dpi scanner with 30 bit color for around $399. Nikon has a Coolscan III that handles both 35mm standard and APF film and negatives at a resolution of 2700dpi. It is around $979. There is also Minolta's Quickscan 35 Plus. It has a scanning resolution of 2800 dpi but only supports 35mm film and slides. At $928.

Scanner Caveats

Things to think about. As you can imagine, all scanners are not alike and as to cheap scanners, you get what you pay for. Why is it that the same scanning resolution can cause the price of scanners to jump from $79 to $499 ? Well, several things will do it. First is the workmanship of the units themselves. You pay for the solid well built units at the higher prices. You also get much cleaner scanning as when you scan, the scanner actually sends a light bar with all those tiny sensors down the image. You don't want any jerking motions or stops along the way. You also get better optics. Finally, the software bundled with the scanner can certainly make a difference. You find that HP and Microtek software has some excellent adjustment features that you can set as the image is scanned.

Other things to check out with the scanner is the color bit depth that is captured. When it is colors you are concerned about, the higher the number the better. At a minimum, look for 32 bit capture. My preference would be to go with a 36bit scanner. Again, consider what your output medium will be.

When looking at the scanners, you will often see two sets of dpi numbers. One being the optical and the second being the "total" or interpolated number. You should always stick with the optical number as it represents what the scanner can physically scan. With the other numbers, the scanner needs to use software or some other method of filling in those dots and that can be very unpredictable.

Connecting your scanner can also be a problem these days with a lot of folks having a lot of equipment on the computer. There are three ways today to connect your scanner to the computer. The lowest cost is the Parallel Port scanner. If you must go this route, then get another Parallel port card installed in your computer. They are about $45 and really make life easier. The second way of connecting scanners is through a SCSI (Small Computer Systems Interface) and this is my current preference. With SCSI cards, you can add multiple devices to the computer. The third interface is the USB (Universal Serial Bus) connector. It is supposed to be even easier to connect than any other device but you really should be running Windows98 on your computer. Most scanners today do not have the USB connectors. Also, one other problem coming up with the current crop of USB Scanners is that they are very power sensitive, if it doesn't work, plug the scanner's power directly into a wall outlet.

Scanned images can take up quite a bit of space on your computer. The higher the resolution, the larger the original image, the larger the file size you will be working with. One major problem of scanning at the very high interpolated scan rates is that it creates such very large files that you find that the image editing software cannot handle it and it or your computer crashes. You can never have too much disk space or memory on your computer. Some scanners will tell you before you actually scan the image as to how large the image will be, place close attention to it. For example, the small thumbnail images you see on web sites are often 10K in size or less while larger images can go upwards of 50mb.

My favorite scanner ??

My favorite scanner is one that I can't afford but when I did settle on one, I picked the Epson Perfection Photo 1200U. USB for quick connect and fast scans, the 1200 actually goes up to 2400 dpi optical, and the Photo part for the top head scanner to do photographs and negatives dispite what I said about the kind of resolution you will need to scan and print photos and negatives. Most of my work will be for the web so I compromised here so that I could actually scan in the work. About $200.


I have found some excellent resources pages available on the internet. is a comparison of the Nikon Coolscan and the HP Photosmart. a comparison of film scanners. is HP's Photosmart page. is Kodak's digital scanner page. is Nikon's scanner page. Microtek scanner page. and my favorite, Wayne Fulton's scanner tips page.

I hope all of this helps you in determining what kind of a scanner to look for. Key issues will be the type of originals you will be working with whether they be prints, film, slides, or some odd sized negatives. The Second issue is how much you will be enlarging them for printing. This can have a significant cost on both the resolution you need to scan at and the cost of the scanner. Happy Scanning!

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Copyright 2001 Sanborn Software Systems LLC
This Page Last Updated: February 5, 2001.