programming and human factors
by Jeff Atwood
I've always wondered why digital cameras express their resolutions in terms of megapixels, rather than the typical pixel height and width numbers you find on computer displays. Nobody buys a 21" LCD with 1.9 megapixels of resolution; they buy a 21" LCD that can display 1600 x 1200. But they're technically the same thing: 1600 x 1200 is 1,920,000 pixels, or 1.9 megapixels. It looks like we're using the old hard drive manufacturer's trick of dividing by powers of ten.
One problem with using the megapixel designation alone is that you have no idea what the aspect ratio of those pixels are-- 16:9? 5:4? 1.33:1? Who knows, maybe that 1.9 megapixel camera is really taking 192 x 10,000 pictures. Pixels are pixels, right?
The wikipedia entry on computer display resolutions has a great chart that contrasts the most common monitor resolutions, along with the ratio line that each falls on:
It's interesting to note that the most common monitor resolutions (800x600, 1024x768, etc) are 4:3. I didn't realize how oddball the 1280x1024 ratio was. The widescreen variants are really catching on quickly, too, if the current LCD monitor selection at Newegg is any indication.
But the alphabet soup of display designations isn't doing anyone a favor, either. I'd much rather know that a display is capable of 1600 x 1200 instead of the cryptic designation UXGA.
You can compare the different resolutions of most common electronic devices (cameras, screens, video, etc) and many common formats using this nifty dynamic megapixel overview tool. Some of the camera models listed tend to have 4:3 aspect ratios, like PC displays. But not all. The 3:2 ratio is also common. Here are a few samples:
Evidently the 3:2 ratio derives from the native dimensions of classic 35mm film.
I think most print out the essential technical specifications on the package. But when it comes to having it out on the shelves, the only thing the vendor does mention is megapixels. It is how they do it here in Sweden.
I'm very annoyed by that term... "megapixels". I find it counter intuitive since it, as explained with ratios, doesn't actually tell much about the resolution that the device can handle.
When I'm out to buy a camera and working with digital imagery a lot, the knowledge of how many pixels a camera can take is secondary. I'd rather want to know the height and width resolution since I'm used to that, and I'm rather bad at doing division calculations in my head. And I guess the sales clerk won't be much of a help either. :)
Spike on May 28, 2006 3:44 AM"A corollary of this is of course that the pixels on your 1280x1024 monitor aren't square."
They are square, the panel itself will be 5:4. (AFAIK, I've never seen an lcd monitor that has non-square pixels)
3:2 does indead match 35mm frame and therefore also matches the normal aspect of the most common photo print and frame size of 6in x 4in.
The whole aspect ratio mess gets even worse when you also include the standard sizes for enlargements and frames:
6in x 4in = 3:2
7in x 5in = 7:5
10in x 8in = 5:4
15in x 10in = back to 3:2 fortunately
On digital cameras larger 'pixels' are be better in the case of a larger sensor - you get greater sensitivity with lower noise.
On the countrary they are worse in the case of lower pixel count on the same sensor size :)
So basically the pixel size doesn't tell much without knowing the sensor size for example.
M.K. on May 28, 2006 8:32 AMYes it must be stressed that 1280x1024 displays still have square pixels. They are "tall screen" displays!
DVD's still have non-square pixels though. The 720x480 pixels get crammed into a 4x3 or 16x9 ratio, both of which have to squeeze the pixels one way or another.
Chris L on May 28, 2006 9:56 AMbut it's not really all that interesting to note that 4:3 is common
Well, there are a couple things of interest here.
1) As resolutions increase, specifying the width and height becomes increasingly meaningless. Sure, the difference between 1024x768 and 1280x960 is clear enough, but what about 3264 x 2448 vs. 4368 x 2912? As displays get larger, mexapixels-- when expressed with the aspect ratio-- might be the way to go. DPI might be of interest as well.
It might take a radical change in display tech for the numbers to get that large, but it'll happen in our lifetimes. Eventually megapixels, DPI, and aspect ratio will be more informative than h x w.
2) The aggressive adoption of widescreen ratios that deviate from 4:3. Seriously, check out the newegg LCD selection. A ton of them are widescreen. I definitely don't remember this many widescreen LCD choices a year ago.
3) The 3:2 ratio and its relationship to 35mm history was pretty interesting, I thought.
Jeff Atwood on May 28, 2006 11:11 AMAlso note that for oddball sizes like 1280x1024 (and I've also seen 832x624, I think), it allows you to have a 4:3 space that isn't intruded by the menu bar, task bars, docks, icons, toolbars, etc.
Darrin on May 28, 2006 11:19 AMFactory, that's a brilliant comment! Talk about unstated assumptions.
I'd just assumed that my LCD monitor was 4:3 and therefore the pixels wouldn't be square. Measurements show the screen to be about 336mm x 267mm which is a ratio of 1.258 which is about 5:4.
So, the pixels are square after all. I've been too used to systems that have odd screen resolutions and non-square pixels, but that is no excuse. Our assumptions about how something is, based on our experience, aren't worth anything. For every thing that we ever do we HAVE to check our facts.
My experience of doing computer graphics for TV work has shown that square pixels is not something to be taken for granted. Clearly the opposite is also true - just because something is an odd ratio doesn't mean that the display is 4:3 or 16:9. There is no way that I could have (or did tell) that the screen I look at every day was 5:4.
Thanks Factory for putting me straight, and I can assure you that I would have thought the comment equally astute if you were right OR wrong. You were right so that's even better :-)
It's also interesting to note that the two most common aspects are squares of each other: 4:3 becomes 16:9 for widescreen.
A corollary of this is of course that the pixels on your 1280x1024 monitor aren't square. I haven't written anything other than web applications for years now so I'm not sure where the correction for this is done within Windows.
I do know that it causes me a problem when I make wallpapers though (http://www.kirit.com/Categories:/Wallpapers). Do I correct or will the OS do it? Is the answer different for Macs or for Linux? I really ought to get out the ruler after drawing some circles to find out.
Kirit on May 28, 2006 1:11 PMThat's a nice overview, but it's not really all that interesting to note that 4:3 is common... because that's the aspect ratio of standard television. Duh. :)
Chris Nahr on May 28, 2006 1:33 PMThe other annoying trend (In the UK, at least) is for computer stores to quote laptop screen sizes in inches only, leaving no clue whatsoever about the resolution or aspect ratio. Your need for a laptop with a 17 inch screen may be more related to failing eyesight than it is to a demand for screen real estate or the desire to playback DVD movies in widescreen, but some meaningful information would go a long way.
Bob Armour on May 30, 2006 7:21 AMIf you use a CRT monitor, though (which I still prefer), it's (almost?) always going to be 4:3 ratio. So you better watch what resolution you pick if you want things not to look squashed/stretched.
Atario on June 5, 2006 12:30 PMNTSC video is 4:3. (EIA/RS-170A)
Don't care what wikipedia says....
I think, real problem is that available resolutions of digital cameras never match most common resolutions of monitors - SVGA, XGA and SXGA. Impossible to show on internet native shots.
Den on December 15, 2007 8:49 AMI use 1280 x 1024 and I never knew that it was 5:4. Interesting. Not that it's ever affected me.
Reece on February 25, 2008 3:04 AMI usually have to resize my pictures anyway to be practical for web use. However, I did get an awesome SUPER PC multi-monitor computer from http://Multi-Monitors.com so it makes things a lot easier when you spread the photographs across four screens! This quadruples the resolution available for viewing. Here's what I have...
http://www.multi-monitors.com/Samsung_Multi_Screen_Display_Multi_Monitors_com_p/4lcds02.htm
Here's a cool youtube video of what I'm talking about:
http://www.youtube.com/watch?v=j_avGStqZOI
Multiple Monitors on September 4, 2008 6:35 AMDepending on the intended usage of the camera, the 4:3 vs. 3:2 ratio is important, and yet is a feature that you hardly see mentioned in reviews or anywhere else.
For mostly viewing on a computer screen, the 4:3 is better (Well, if you're using 1024x768 like I do for example). But for people who like to print most of their photos like with regular film, a 3:2 ratio camera will be better since it can spare them always finding the "developed" pictures cropped.
The comments to this entry are closed.
Subscribe in a reader
Subscribe via email
|
|
Traffic Stats |