Easy ‘Life Posters’ with Picasa 3 beta

I like Life Posters. They look good on the wall, and make great presents. But before today they were irritating to make.

A couple of years ago I put one together for Dad’s birthday. It wasn’t a fun process. I wanted a seamless grid of non-cropped images, and I couldn’t find anything to generate it for me. I didn’t have Photoshop at the time, so I needed cheap/free options. Picasa 2 could build collages, but only by cropping each photo to a square. Everything else could generate contact sheets, but with ugly gaps between the images, particularly when I mixed portrait and landscape shots. I also struggled with spatial concepts – if the final output has a ratio of 3:2, would a 9×6 grid of 3:2-ratio photos fit properly? This confused the hell out of me, and I kept getting it wrong. In the end I only used landscape images, and managed a seamless grid after a lot of trial and error with the XnView contact sheet generator. If I did it again, I’d just build it manually in Photoshop.

Except now I don’t have to, because the new Picasa 3 beta has extra collage options that make life much, much easier. Its ‘mosaic’ collage will arrange any photos into a fixed ratio, without gaps or cropping. That’s pretty clever. I’d love to see the algorithms figuring that out. I made this in two minutes, using images from my enormous ‘To Flickr’ folder:

I think that makes for a much more interesting poster. It has both portrait and landscape images, and all neatly arranged without whitespace. Picasa also handled the different aspect ratios: there are some square images in there, and even a 5-image panorama (it’s above DJ monkey). The layout isn’t fixed, either – you can hit ‘shuffle photos’ to produce a different design.

But Picasa has another trick up its sleeve. It lets you choose various aspect ratios for the collage, but it always produces images with a long-side length of 5120px. So there’s a lot of leeway for large prints.

For example, a portrait A4 mosaic is 3621x5120px (with a default setting of 72dpi). If you print this on A4 you’ll get 451dpi, which is very, very high (300dpi is magazine quality). In fact, you could easily use it for A3, where it comes out at ~300dpi. So A3 isn’t officially supported, but works anyway. And this obviously applies for all the other ratios.

Dad’s life poster was made into a 30″x20″ canvas print, for which I had to supply a 200dpi jpeg. Picasa’s 3:2 export produces a file that’s 170dpi at 30″x20″, and imho you could get away with resampling for the final 30dpi. And if you want anything larger than 30″x20″, you’re probably not using Picasa.

Sadly you can’t specify a custom size (although see the last bullet point for a potential way around this), but there’s a fair range of ratios built in:

  • 5×8
  • 9×13
  • 10×15 (so, 2:3)
  • 13×18
  • 20×25 (4:5)
  • A4
  • Square
  • 4:3
  • 16:10
  • 16:9
  • 5:3
  • Desktop resolution (which, interestingly, also exports to a long-edge of 5120, so you could conceivably fudge this to get any ratio you want. Unless this is a bug.)

I think this will be very useful. I’m impressed with the mosaic collage anyway – the maths behind that must be pretty daunting – but defaulting to a large export is a very nice feature. Thanks, Google.