Monday, July 4, 2011

Bigger than Big

One of the side effects of the megapixel race is very large pictures. Both in terms of file size and image dimensions. It's long past the point of practical use - as I've implied in earlier articles.


A 4x6 print @ 300 dots per inch (normal printing quality) requires an image 1200x1800 pixels. Although "requires" is a bit strong of a word - most printers will upscale an image anywhere close to that without much quality loss. In effect it's more of an upper limit - in that providing an image larger than that result in 'loss' of detail - there's more information than the printer can actually resolve. That's sometimes a good thing, if your 'detail' consists of messy jpg artifacts and ISO noise - stuff you can see at 100% zoom of Point and Shoot camera shots.

A 5x7 print @ 300dpi is 1500x2100

8x10 is 2400x3000

And so on. To a point.

The larger you make a print, the less likely you'll be viewing it from close up. Meaning you can get away with less detail.

Digital displays are even more forgiving.

Facebook pictures are 720 pixels x (up to) 720 (if you make it square, which most people don't) EDIT - Now closer to 1000x1000, but not all that much larger.

An average photoframe is 800x480

Most monitors display a resolution around 1680x1050 - though some as high as 2560x1600 are getting more common. The first of the two monitor sizes is very close to the size of a sharp 4x6 print.

Televisions, although large, really only display 1920x1080 pixels worth of information.


Which brings us, finally, to cameras.

An A3000, which is rated at 10MP (rather on the low end as of the writing of this article) has a number of settings.

They are:

3648x2736
2816x2112
2272x1704
1600x1200
640x480


Or 10, 6, 4, 2 and 0.3 Megapixels respectively -- a Megapixel is the height and width (in pixels) of an image divided by a million (and usually rounded a bit). It doesn't really address Aspect Ratios but it's handy for a rough comparison.

A T2i has a number of settings as well:

5184x3456
3456x2304
2592x1728


Or, according to the camera - 18, 8 and 4.5 megapixels

I'll indulge in a little math at this point - also with pictures if you want to skip the number crunching.

Assuming a 300dpi print, you can divide the above by 300 to get the 'optimal' print size.

A3000
12"x9"
9.4"x7"
7.5"x5.6"
5.3"x4"


(I'll omit the lowest setting, 640x480 is only slightly smaller than the current FB size, and is a decent size for emailing pictures)

To visualize the above
A3000 size comparison



T2i
17.2"x11.5"
11.5"x7.6"
8.6"x5.7
"

T2i size comparison


So, what does this mean? As covered in the last article, storage space isn't really at a premium most of the time. If you have a fairly good idea of what you're going to do with your pictures (and how much will likely be cropped out, or re-sized) you can probably back your camera off *Max* settings though. If nothing else, you'll be able to copy and email your pictures more quickly.

Myself, if it's something in the backyard that isn't moving and I already have quite a few pictures of it, I'll drop down to Medium (8MP) - and probably Normal Quality (previous article) as well. I can still print an 8x10 as long as I use most of the picture. For Facebook, 4x6 prints and general computer viewing - it's more than overkill.

50% File Size - 95% Quality

I've read a few articles on Image Compression. That's where you specify if your camera is taking Superfine, Fine, or Normal quality shots. Different brands (and years) of cameras have different names for this - but it boils down to the same thing.

Most of these articles suggest that, if you have the room, you should *always* set your camera to the highest quality and highest Megapixels. However, most of these articles are at least three years old - which is a very long time ago in terms of technological progression.

Not a lot of them include examples either - which would still be outdated, but at least would give you an idea of what to expect.

Of the few that do give examples, they tend to magnify them to the point where the difference is actually visible (300 or 400%) which doesn't strike me as particularly 'Real World'.

So without further ado....

Compression
High Quality above, Lower Quality below.

As you can (probably?) see, the top image is slightly better. The edges of the leaves are sharper, and there is less compression artifacts around the web (which somewhat exaggerated due to motion blur). There is also a bit more dynamic colour range in the top photo. It's also twice(!) the file size.

Is it worth it? This is where most other sites would say 'Yes, if you're going to print it - memory cards are so cheap - go with highest quality'. A few sites will (paradoxically) suggest that you switch to lower quality *when* you start running low on space i.e. when it's already too late. In my mind, having (at least) twice as many pictures for a rather imperceptible change *is* a very good tradeoff - and much better started early.

There's also a psychological advantage to that as well. If you assume that 'Highest Setting' means 'Best Shot', you probably won't take a second picture, even if you probably should. If you have twice as many pictures remaining, it's a lot easier (mentally) to spare the room for a 'Backup Shot' - even if it's the difference between having 2000 pictures remaining or 1000. It's worth noting that some of the pictures were up to 4x smaller on the lower compression mode of the T2i - it varies a lot between cameras and shot content.

When taking the pictures for this article a rather high number 'messed up'. Either they weren't in focus - The A3000 shots (not shown) had half of either pair blurry - so weren't worth putting up. They looked fine on the camera preview. A significant number of the SLR shots had a different area in focus, or motion blur. In not a few shots, the smaller file size shot was noticeably better than the larger. In other words - it was much more likely for *something else* to go wrong, than for compression to mangle the image.

You mileage may vary, especially with an older camera. It's worth looking into though. Memory cards and Hard Drive space *are* relatively plentiful and cheap - but still finite.