Scan and Shoot - Resolution

Scan and Shoot – Resolution


What an odd title, you say. Few people ever think about the desktop scanner as anything more than a way to digitise documents but you would be missing out on a whole barrel of talent if you ignored the power of a scanner.

The shame is that, just as I write this message to all you fans of the digital image, the scanner is in the process of being submerged beneath a whole barrage of other functions.

Canon MPC-100 multi.jpg

The multi-purpose device is upon us. Now, for very few dollars, you can buy a device that not only scans a document but copies it, prints it and faxes it.

While these are perfect for the small office and the person who has little need for a high level scanner alone they confuse matters IMHO.


I’m a scanner-only sort of feller and can happily sit down with a pile of ‘stuff’ and spend a whole morning just scanning, scanning and scanning. Later on I will make my prints and send my faxes (to be honest, I just gave away my fax machine to a charity shop!).

However I do have many friends who find the scanning business a bit daunting and frequently have early trouble with the matter of resolution.

Right Res

With a computer monitor, the scan resolution determines image size — on screen. This is known as the display resolution.

In my own case, my monitor is capable of displaying up to 1680×1050 pixels. If I select this setting all the on screen items, like hard drive icons, documents I leave on the desktop will be fairly small. In my book, too small … so I use the 1280×800 setting. If I chose an even lower setting, say 1024×768, I find the on screen items are soft edged … not to my liking. This is an important lesson and playing around with your monitor settings will probably teach you more about scanning than many other exercises.

The key element in the whole scheme is that a specific digital image will look far larger on screen than it does on a print. Why so?

Because screen pixels are bigger than the tiny dots that an inkjet printer can imprint on a print.

Look closely at your screen. See the pixels?

Now look at a decent inkjet print. See the pixels? Betcha you cannot!

Basically, the answer lies in the size of each individual pixel and the resolution of the monitor. In my own case (using a Macintosh) I figure the screen resolution to be around 72 ppi (pixels per inch). I know that many Windows users figure their screen resolution at 96 ppi. Others may work with a screen resolution of 100 ppi or more. It’s up to you but the key fact is that a monitor is a low resolution device

The above is important if you scan images for sending by email and only for viewing on a monitor. For one thing, the file size is smaller and, for another, you can scale an image to just the right size on screen.

A printer is a high resolution device. The usual method of printing is to set the image resolution at 300 ppi but you can also go down to 225 ppi and still get a reasonably sharp image.

So, in the scanning process, if you want a final print of 10×8 inches work backwards in your image editing software and, if the ppi figure settles at about 225 or 300 ppi, the print will be acceptably sharp.

CanoScan 5600F_A1.jpg

With current digital cameras you can happily rely on getting heaps of terrific 6×4 inch prints — and even 10×8 inch prints — from the camera’s image sensor, which is often of a far higher resolution.

Back to scanning: open your image in Photoshop or any image editing software or even the dedicated software that came with the scanner, select the final size you want (for email use or for printing) and let the software determine the resolution.

Problem solved.

Monitors are effectively TV screens — video screens — and these are very different to printers. Printers hunger for inches, but monitors don’t care about inches — or centimetres!

A monitor is usually larger than our photographs. Some people often scan at higher resolutions to fill the screen, so increasing the file size but there’s no advantage in messing with huge images; the pixels will be lost when the image is displayed on screen.

Read more from our Cameras & Equipment category

Barrie Smith is an experienced writer/photographer currently published in Australian Macworld, Auscam and other magazines in Australia and overseas.

Some Older Comments

  • Dan July 10, 2009 10:18 pm

    Adjusting screen resolution to make things bigger or smaller on a Windows OR Mac system is just a recipe for degraded images and eye strain. Particularly since the article suggests 1024 x 768 as a potential candidate for a monitor that usually displays 1680 x 1050. That's a whole new aspect ratio! Welcome to a world of blurry AND stretchy.

    I'd like to see this article re-written, but by someone who has a stronger grasp of screen resolutions, pixel density and scaling.

  • Steve Hollasch July 10, 2009 11:40 am

    What resolution should I use for scanning old 4×6 prints? I just want to digitize these prints for a slideshow to give to my kids on DVD.

    Is this DVD for posterity, or will they have access to the originals in the future? What seems high-res today will seem low-res in the future.

    Will your slideshow use the technique of displaying a slowly-moving window over a zoomed-in photo? If so, then you'll need to use an image resolution higher than their monitors.

    In general, I'd make the slideshow at native resolution, as long as the DVD can hold them all, and the slideshow software can manage them. Downsize the images if the collection is larger than the 4.7GB of a DVD or if your software can't handle them.

    I suspect you don't need to downsize the images at all.

  • Kim Groth July 10, 2009 11:28 am

    ... and for the next time. Keep away from topics you don't understand. Some of the comments above point pretty severe faults out.

  • Kim Groth July 10, 2009 11:21 am

    Do not adjust your screen resolution in order to get your icon to be the right size (that's a windows thing). Rightclick (or option-click) on your desktop and select "show view options". Adjust your icon size and turn that screen res back up again!

    Great article by the way.

  • John Gilbert July 10, 2009 02:36 am

    I've met far too many people who set their LCD monitor to something less than the native resolution. This bugs me because everything gets blurry. This technique would work fine in the days of multisync CRTs, which have no fixed pixel grid, but not for flat-screen technology. Setting your display to high-resolution and high-ppi can cause issues with web pages, though, where text is defined in points while images are defined in pixels.

    For the same reason, I don't understand why middle-of-the-line HDTVs have a native resolution of 1024x768 (or 1366x768). 768 doesn't match or divide cleanly into of the native TV formats of 1080, 720 or 480. Every single picture format will have to be resampled to the native TV resolution, thereby degrading the picture quality.

    Lastly, older Mac displays were designed to be roughly 72ppi based on the graphic arts standard of points and picas. A 19" monitor had a fixed resolution of 1024x768, and a 21" was 1152x870. These days, monitors generally have upwards of 100ppi. Saying that your monitor is 72ppi based on it being a Mac clearly demonstrates a misunderstanding of the concept of pixels-per-inch and dots-per-inch.

  • Shirley Schweizer July 10, 2009 01:50 am

    What resolution should I use for scanning old 4x6 prints? I just want to digitize these prints for a slideshow to give to my kids on DVD.

  • Steve Hollasch July 7, 2009 05:18 am

    Ugh, I couldn't disagree more. 100dpi is still far too low, in my opinion. I personally can't wait until we finally get 200dpi monitors for normal work. We don't settle for pixellated print, why do we settle for low-resolution screens (and then complain about how painful it is to read documents on a monitor)?

    The crux of his error is the statement that "too many pixels" will make his display elements too small. Far better to set the highest resolution your setup can handle, and then fix up the display elements. In Windows, this means going into the advanced display properties and setting up the ruler correctly, so you that your monitor now actually display elements at their proper size. In fact, 10pt text will now render at ... ten points! Then scale up your icons and text to a level you want. You now have a high-resolution display with elements sized to your liking.

    Crippling your display, and then yoru scanned art and everything else in your workflow, is just batty.

  • Fletch July 6, 2009 11:01 pm

    "Why the odd title, you say"

    I did!

    Then I read on a realised why the need for the odd title. Its because if the title was a bit more descriptive nobody would read the article! I didn't reach the end.

  • michael July 6, 2009 11:36 am

    There's the old saw about 72 DPI screen resolution for a Mac. Look at specs for current models. There's not a Mac sold, and since monitor sizes are pretty uniform, few PCs that have a resolution lower than 100 DPI.

  • Lisa July 6, 2009 04:21 am

    I appreciated some details of this article that despite scanning many images for various uses in the past five years, I had somehow missed, like why hadn't I thought of working backward to get the file size I wanted before???

    HD's may be "cheap" relatively, but I cannot afford them now. My 6 year old computing power processes large scans and large files so slowly that they can be timed with a calendar at times. So while the capability is out there for "big as possible" it is unattainable for me at this point, so it's do the best with what you've got.

    Thanks for the tips.

  • Wayan suadnyana July 6, 2009 04:16 am

    i agree with reznor...

  • Reznor July 5, 2009 09:55 pm

    And I really don't think, it's reasonable to tell people not to scan at high resolutions. Who cares about file size? HDs are cheap. You should always scan at the best quality possible, it's easy to reduce detail and file size but try to increase an image... quality's gonna suck. You might lose the original document, it might be destroyed or whatever. In that case, wouldn't you want the best scan you can get out of your device? You never know if you might need that picture or whatever your scanning for another purpose than just looking at it on screen. Maybe you do wanna print it some day, cause the original is gone. If that happens, you're gonna hate yourself if you scanned at a low resolution thinking, you'd only look at it onscreen anyway.

  • Jono July 5, 2009 05:05 pm

    TL;DR - what is the point of this article? Perhaps a tidier writing style would make me want to read this, perhaps making a summary?