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UMAX Astra 2100U Scanner Test Review
09 June 2001
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Pleaee help KenRockwell.com

Mandatory: learn all about scanners and how to select the right scanner here

See comparative review of $320 Epson 1640SU Photo here.

See comparative review of $1,500 Microtek Artix 1100 here.



This tempting scanner can give great scans, unfortunately the software required to run it crashes both Macs on which I tried it, and it rewrote system files on the Win2000 PC I on which I tried (unsuccessfully) installing it.

It is incompatible with a Mac running iTunes 1.1 software. UMAX says they are working on this as of March 2001. Good luck!

It also made a 350MHz iMac completely unstable and unbootable. It took over an hour for of one of the most kind-hearted Mac specialists in San Diego to get it running again.

Another reader in Chicago wrote ME trying to get my help in getting her system to run. UMAX couldn't get it to go. That's too bad, because I gave up myself. Hopefully UMAX will take back her scanner.

This is the cheapest flatbed scanner I could possibly find. It cost $50 and had a mail-in $20 rebate, so it cost $30.

Sooo, if you are still crazy enough to be reading this far, on the few occasions on which I did get it to go before I got rid of it:

It has 600DPI resolution, which is far better than you will even need for scanning flat art for printing on your inkjet printer or use on the Internet and email. 600DPI is technical overkill as you know if you read the mandatory scanner basics referenced above like you were supposed to.

As I suspected, it works great for scanning flat art like photo prints.

You only need to spend serious money when you need to scan film.

Unless you are a fine artist for whom your prints are the final manifestation of all your creative ambitions, the best scans come from scanning the original film and not scanning prints.

Scan Times

Here's what I measured on a Mac G4 450 MHz Dual-Processor, deliberately mis-connecting the USB connection through my Mac keyboard which in turn was connected through a cheap USB hub to the computer, scanning through VistaScan Twain 3.5.4 into Photoshop 6.0 for an arbitrary 3.5" x 3.5" piece of flat art, in Minutes:Seconds:

No Descreening
133 LPI Descreen

As we can see, when asking the scanner to descreen (used for making scans from magazines and other printed material that are halftoned) the scanner scans at its maximum resolution, low pass filters, and then resamples to the selected resolution. In English that means that it takes a little longer, but greatly improves quality for copying images from printed material.

I find the descreening function give better scans for all originals when your desired output is at low resolutions like 72-100DPI. If your final output is around 300DPI or greater you'll probably get better results scanning without descreening. Of course if your are copying from halftoned art (books, magazines and brochures), you ought to to use the descreening all the time.

Descreening, because it scans at the highest resolution regardless of the final resolution you select, can take forever for scans of a whole page. For a scan of an 8x10" original at 100DPI it took just 45 seconds with no descreening, and three full minutes with descreening.


The 2100U did a swell job delivering scans at any selected resolution. Images were properly resampled.

This is in contrast to the all-in-one Microtek ScanDeck, which when set to resolutions below its maximum of 300 DPI gives nasty alaised images. With that stand-alone office scanner one always needs to scan at 300 DPI and do the downsampling in Photoshop, which of course wastes lots of time scanning and then having to play with it in Photoshop.

The Myth of 36 Bit Scanning

Even the dumpiest scanners today brag about 36 bit scanning, and so does this one. That means that at best they use an analog-to-digital convertor that just happens to have 12 bits coming out of it to digitize each of the signals from the analog outputs of the CCD preamplifier for each of three color channels (red, green and blue).

Even worse, in this scanner a bogus "bit enhancement technology," or "BET," is used. All that means is that they take the 8-bit per channel results and re-dither (deliberately add noise) to each sample value and feed you the results with 12 bits of precision in the math. So what does that really mean? It just makes your files sizes double what they ought to be to clog up your hard drive.

If this sounds technical, it is. If this makes no sense to you, that's my point.

Let's explain why more bits are better, then I'll explain why this make no difference on scanners in this price range.

We only can see between 6 to 8 bits per channel log (18 to 24 bits per pixel) at best.

The reasons a scanner would like to have more than 8 bits per channel is that is so that one can 1.) convert digitally from linear analog input to log digital output instead of doing the process in analog (in other words, resolve fine differences in the black areas of the image) and 2.) to allow further fine-tuning of an image in the higher resolution so that one still has 8 good bits per channel (24 bits per pixel) after all the image tweaking is completed.

One looses accuracy in every 8 bit Photoshop operation, even though all the bits are still there. Mathematical errors accumulate with every operation, just as you would if you always had to write down your results from balancing your checkbook with only 4 digits. You need 16 bits to represent the product of two 8 bit numbers, so when the answer has to be truncated or rounded or redithered back to to 8 bits you loose something. If you only start out with 24 bits, by the time you get done in Photoshop you have lost a few bits of accuracy due to all the small mathematical errors. By starting with and working with more buts you can easily preserve your accuracy. This becomes critical if you are playing with levels and curves.

Scanning in the 36 bit mode into Photoshop 6.0 lets you attempt to retain plenty of bits of accuracy even after a lot of Photoshop tweaks. This is good.

Here's the problem: The noise of the CCD and it's circuitry completely cover up any of the precision the A/D convertor might have. At best the noise level of this scanner is at about 30 bits per pixel, and probably even more. ALL THE EXTRA BITS ARE DOING IS REPRESENTING NOISE.

If this were a $80,000 photo-multiplier tube (PMT) based scanner you might have enough signal-to-noise ratio coming from the image sensor (that tube) to justify a 12- or 14-bit per channel A/D convertor.

These CCDs simply don't yet have the signal to noise ratio to justify the high-bit ADCs.

Therefore, ignore people who work in computer stores and try to get you to believe that more bits are better, and can't even explain exactly what the extra bits do. In this case they mean nothing.

Even worse, unless you are using the newest version of Photoshop 6.0, very few computer programs even can read anything other than 24-bit (8 bit per channel) images. The JPEG (.jpg) format only works in 8 bit mode, for example. If this is your case, the only advantage to more real bits inside a scanner is if the scanner was doing some signal processing in the digital domain in which case more bits could be better. Hopefully by now I've convinced you that these internal details are meaningless taken outside the context of the entire system design of a scanner.

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