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The confusing and mystical world of aspect ratios.

December 23, 2011

Aspect ratio is conceptually very simple-just take the two dimensions and express as a ratio. Old tube TV sets were, for instance, approximately 4:3 and current rectangles showing different aspect ratioswidescreen TVs are usually said to be 16:9.

Movies are a confusing mess with aspect ratios all over the place—I’ll ignore that for this post.

Common aspect ratios found “in the wild”

Aspect ratios are simple in principle, but in practice things are a bit more messy and it affects what images look like when printed or viewed on a screen.

Here are two tables of various aspect ratios that you’ll run across in various contexts:

Paper dimensions (inches)             Aspect ratio

10

7.5

1.3333

4:3

PowerPoint’s default printable or useable (1,2)

11

8.5

1.2941

Normal US paper size, common European sizes are 1.41

Photographic and television ratios

3

2

1.500

3:2

35mm film, 4×6 prints, digital camera option

4

3

1.333

4:3

Tube TV approximates this, default for many digital cameras (3)

7

5

1.400

5×7 print size

10

8

1.250

8×10 print size

12

8

1.500

3:2

“no crop” large print size

16

9

1.778

16:9

widescreen TV, digital camera option

16

10

1.600

16:10

many widescreen TVs are really this, some digital cameras (3)

Notes:
1. paper printing maintains this on 8.5 x 11 paper
2. displayed, aspect ratio is maintained, fill the height, black bar the width
3. sensors in digital cameras vary in dimensions, many approximate 4:3

PowerPoint Slides
This whole post started when I got curious about PowerPoint slide dimensions. As shown above, PowerPoint will, by default, give you a slide that’s intended to be 7.5″x10″ when printed, a normal 8.5″x1 1″ page with a .5″ margin. On a screen, the margin doesn’t show, so that’s exactly a 4:3 ratio, a perfect match for older monitors and TVs. On a widescreen monitor, black bars fill the gaps on the sides so everything on the slide stays proportioned.

Pictures and cameras
Notice what that means for our discussion about using images on slides:  to fit the PowerPoint slide proportions without cropping, the image will need to be 4:3, but many images aren’t.  From 35mm film they’ll be 3:2 and from a digital camera they are commonly 4:3, 3:2 or 16:9. (Most digital cameras allow you to select one of those with 4:3 as a common default.)  This is one reason that an image might not work full frame on the slide-fixing an aspect ratio mismatch by stretching the image out to fill out the frame will introduce distortion and that’s a definite ‘no no’.

Image with a pair of digital camerasDigital camera sidebar. The sensor in your camera has its own physical and pixel dimensions: its own aspect ratio. Of those I know about, they generally approximate a 4:3 ratio, a few are 3:2, but it’s rarely exact in any case. Interestingly, that ‘xx’ megapixel camera you’ve got probably isn’t creating images that size, especially if you select an aspect ratio other than the one that was used to rate the camera with. For instance, my current camera, a Fuji HS20EXR, is rated at 16M pixels.  The max pixels stored is actually 15.9M if the 4:3 ratio is used.  Set to 3:2 it stores ~14M, and at 16:9 it stores ~13M pixels.  The reason is simply that the camera adapts to the chosen aspect ratio by ignoring part of the sensor to get the ratio right.  If you care at all, I suggest you ignore the “wasted” pixels–if you’re going to use the images in 16:9, shooting them that way in the first place will help prevent images that can’t fill a widescreen monitor or T V.  On the other hand, a 3:2 choice will give images that are proportioned right for those 4 x 6 prints and it’s also the choice that requires the least cropping to get to either of the other two ratios. I generally use 3:2, but just pick something and don’t worry about it much, just realize that no one choice is going to universally right.

Trivia note: the ‘golden ratio’

Greek letter phi

Symbolized as Phi

Since ancient times artists, architects and philosophers have been using a particular proportion ratio believing it to have special appeal, even mystical significance.  Known as the golden ratio, it’s approximately 1.618 which is pretty close to 16:10.  Interestingly, if you check carefully, a fair number of widescreen TVs aren’t actually 16:9, they’re 16: 10.  And the pixel dimensions for the native mode for the monitor I’m using right now is 1680×1050, exactly 16:10. See?  mystical significance! 😉

Monitors and digital projectors

picture of an LCD monitor.What we create in the form of slides or pictures is only one half of the puzzle.  No matter what it looked like natively, the other factor is what happens in the viewing process.  There’s an aspect ratio there, too, and mismatches can have ‘interesting’ results.

Common screen dimensions (pixels)                                                               Aspect ratio

800

600

1.333

4:3

1024

768

1.333

4:3

1280

720

1.778

16:9

720 HD TV

1440

960

1.600

16:10

1680

1050

1.600

16:10

1920

1080

1.778

16:9

1080 HD TV

Back in the not-so-long-ago days of tube-type monitors, the first two entries above were common resolution modes and, not surprisingly, they’re both 4:3 aspect ratios. Now we can set our monitors to a huge array of resolutions and resulting aspect ratios. Exactly how this affects what a slide or image looks like is complicated because there are several layers of software and hardware that can influence things. It gets even worse if you’ve viewing images on a TV, yet more hardware & firmware that can ‘help’ you with how things look.

Bottom line

You don’t need to know much about all this to do a good presentation (or take great pictures). But it won’t hurt either and it just might be the clue you need to understand why that slide or the picture is either perfect, or close-but-no-cigar.

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2 Comments leave one →
  1. December 23, 2011 03:16

    thanks…..I think!, I need an asprin..lol

  2. December 23, 2011 20:43

    Yeah, it’s a wonder that it ever comes out right.

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