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Let’s start with the basics. There are actually only 3 types of scanners available. They are flatbed, film/slide, and drum. Despite the difference, both flatbed and film scanners all share the same fundamental operational theory. They both use a light source to reflect the image onto a mirror, and the mirror reflects that image to the camera thru a lens. Then, the light/color sensitive elements behind the camera translate the image into digital data and then sends that data to a computer. There, you can save the image as a file, view it, print it or edit it with a photo editing software. More on the drum type later.

The differences on these scanners are how they get the image and how well they can see the color of the image. Since the flatbed type is the most popular one, we will discuss it first.

But before we go on any further, we should first understand some of the terms that are going to be used here:

DPI is short for Dot Per Inch (Sometimes also referred to as PPI ­ Pixel Per Inch). This is a unit to measure the density of an image in a square inch. Higher DPI means higher image quality. For example, if you scan a photo with 150 DPI setting and another one with 300 DPI, the 300 one will give you a better image quality because it contains twice as many dots on the image (finer details).

Digital color decoder is how well the hardware inside a scanner can translate the digital data from a scanned image into color, also known as Color Depth, which is measured by a Bit. One Bit equals one color, and is usually used for scanning B/W line arts. Then it goes to four Bit/16 colors and 8 Bits/256 colors. Although both four and eight Bit can show a number of colors, they are intended for use on B/W graphics or photos. 16 Bit has 65,536 colors (High Color) for color graphics, and is great for use on web pages. 24 Bit has 16.7 million colors (True Color), suitable for printing photos. Some newer ones are capable of providing 32 and even 36 Bit of color depth. But bare in mind, until the recent latest release of Adobe ® PhotoShop 6.0TM, most other professional photo-editing programs can only handle an image with information up to 32 Bit. The rest of the extra information would be discarded, or worse, will not import the image into the program.

CCD (Charge-Coupled Device) means a device that is sensitive to light and color. It’s the heart of a scanner. The quality of a scanned image is dependent on it. It is measured by DPI. A CCD camera has a 300 DPI Native Optical Resolution which means it has 300 light/color sensing elements on it. But it is still possible that the camera could be colorblind. Why? See D Max below for answer.

Resolution is measured by DPI or PPI. It determines how many DPI/PPI the camera and the scanning software can see.

Native Optical Resolution is also measured by DPI or PPI. The number tells you what the maximum DPI a camera can see without the aid of any software. When choosing a scanner, this number is important. We’ll explain this later.

Interpolated Resolution is also measured by DPI or PPI. Most of the scanner manufacturers like to use this number to advertise their products because they seem impressive. Often they claim to have 2400 DPI resolution or higher. But this is not the Native Optical Resolution as mentioned above. This resolution can only be achieved with the help of the software. How do they achieve such a high resolution? The simple answer is by guessing. Yes, the software collects all the data from a scanned image. Then, it calculates the color depth from each true pixel and it generates a set of similar color pixel to place between the real ones until it fills the entire image to the resolution that you have specified before the scan. It will be fine for home use or if the image is to be viewed from the computer monitor or printed on an 8.5” x 11” piece of paper. But it won’t work if you are planning on using the image for large format printing. Because once you enlarge the image you will see all the artificial pixels that the software has inserted for you.

D Max is the color density that a given camera can see, ranging from 0 to 4.0. A normal pair of human eyes is 4.0. The lower the D Max, the less color it can see. A scanner that can achieve 3.0 is considered good. You will only see this number listed on those medium and high-end models. I have seen some flatbed scanners have 3.40 D Max factor. If you need higher then that, you will need a drum type.

Flatbed Scanner:
Since the flatbed type is the most popular one, let’s take a look at them first.

A flatbed scanner is versatile and easy to use. You can scan almost anything that will fit onto its scanning surface. You can even scan 3D objects with it. Their sizes vary, usually about 2 foot in length by 1.5-foot width and few inches thick. You can place them on a desk or a table. Most of them are made to fit a piece of 8.5” x 11” (A4) paper or photo to be placed on its scanning area. Some are larger. I have seen some are as big as an adult full size bed.

Besides scanning photos, some of them can scan slides, negatives and transparencies with the help of software and an adaptor. Basically the adaptor is a small plastic box that is lined with either white or reflective material on its underside, which allows the light source from the scanner to pass through the slide/negative and reflect the image back to the camera. Then the software will transform that negative image into a positive. Also, it serves as a slide/negative holder to hold the film in place for scanning.

Even though a scanner is capable of scanning slides and negatives, that doesn’t mean it can give you a good result because most of the flatbed scanners only have a 600 DPI optical resolution, which does not mean it can give you a good quality scanned image.

A slide or negative has four times higher resolution density as a developed photo. In order to capture the image from them, the scanner should have least 2000 DPI optical resolution to give you a decent result. This is why professional photographers use slides to prepare their publishing materials, such as magazine covers. So if you are planning on scanning mostly slides and negatives, you should consider investing in a film scanner for that purpose.

Some scanners are bundled with Optical Character Recognition (OCR) software, which enables you to scan a piece of printed document and afterwards you can edit it with a text-editing program as if it was originally typed by you on a computer. But it cannot always produce the desired result that the software manufacturer says it can. I always run into a problem with it, especially when I scan a document that contains lines and/or boxes on it, such as an order form. Those lines and boxes confuse the software, and the software doesn’t know what to do with them, so it throws in some garbage characters instead. You end up spending more time editing the document than if you typed it in the first place.

With some flatbed scanners, you can also add an automatic document feeder to it. It acts like a photocopier. You can load multiple documents in the feeder, then it will automatically feed the documents to the scanner one by one. So many functions and accessories can be used on a flatbed scanner. That’s why it is the most popular choice.

Film Scanner:
A slide or negative scanner is also known as film scanner. They have a higher native optical resolution, usually starting around 1800 DPI. They are compact in size because they are designed only to do one thing, film scanning.

Some have a tray that you can pull out for you to place the film or slide in. Some have an automatic film loader, kind of like the dollar bill acceptor unit on a vending machine, pulling your film into it by itself.

Besides having a much higher native optical resolution, the operation theory is basically the same as the flatbed type. The price on these units is typically a bit higher than a regular flatbed scanner, ranging from $500 to several thousand dollars.

Drum type Scanner:
A drum type scanner is a high-end image-scanning device mainly used by photographic professionals. The operational theory is totally different from the other types. It consists of a round cylinder drum to place a photo or film on its surface. It uses a Photo-Multiplier Tube (PMT) as a sensor to capture the image. As the drum rotates, the lens reflects the image to the PMT vertically line by line. And the lens moves across the scan subject (i.e. a photo) horizontally until the entire image has been captured. During the scanning process, the lens transmits the image to the PMT through color filters. These filters are responsible for extracting the colors from the image, they are Red (R), Green (G) and Blue (B) also referred to as RGB. It also detects the intensity of each of those three colors, so it can produce a million shades of colors.

This type of scanner will give you high fidelity color accuracy. But of course, like everything else on this planet, if you want to play you’ve got to pay. A drum scanner price starts at $30,000 each. Plus, you’ll need an expert on board to do all the color calibrations and maintenance to keep it running.

Conclusion:
In order to choose the type or model that is best for your situation, you will need to determine what kind of jobs you do most often and what you are willing to budget on a scanner. With a healthy balance of both and armed with the information here, you should be able to choose the right one.

Author Bio: Larry Chan, owner of Signs Etc. located in Braintree, MA.