I need to do a poster, 8m width by 3.7m height, consisting of photographic elements that will be seen from varying distances. I've talked to the printer and they can do it at 150ppi's.
The issue here is how to work it. Using this calculator I've came to:
= 47244px vs 21850px
memory required = (number of pixels in image ) X (number of bytes per pixel )
47244 x 21850 x 3 (24 bits) = 3096844200 bytes = 3GB
And I'm working on a 3GB computer that, understandingly has to page some information to virtual memory, so it would take some time, however it keeps crashing.
How do professionals work this out?
I'm not really certain what the question is... How to work with large files?
You need as much RAM as a machine can hold and you can afford. 3GB is scraping the bottom anymore. Especially for large files.
A 64Bit operating system and Photoshop running under 64bit helps.
A separate drive (not partition) to use for scratch space will also help speeds.
A good video card with 1GB of RAM on it. Photoshop utilizes the GPU a great deal anymore.
"Professionals" tend to immediately add RAM to almost every system. An adequate minimum would be about 4GB anymore, but even that can quickly be chewed up.
Faster processors and multiple processors also help quite a bit. Generally professionals aren't buying the low-end model of any computer. If anything, more professionals buy the high-end models, especially if they are working on print, flexo, or media other than, or in addition to, web and screen delivery.
As others have noted, buying more RAM is rarely a bad idea when working with images, particularly very large ones.
However, another way to approach the problem would be to design your poster in a vector graphics editor such as Adobe Illustrator or Inkscape. As vector graphics are scalable, they can be rendered at any size or resolution without suffering from pixelization. Also, the amount of memory needed to store and manipulate them depends only on the number and complexity of objects present, not on their size.
Obviously, if your poster includes "photographic elements", then those will have to be embedded as raster images. However, you won't need to scale the photographs above their natural resolution, since the vector graphics renderer will do that for you. (In some cases, you may want to scale the photos up by a relatively small factor, e.g. 2x or 3x, ideally using a high-quality rescaler like PhotoZoom Pro or Perfect Resize, but this depends a lot on how high their quality is to begin with — images with low resolution but high sharpness generally benefit most, while those with a high nominal resolution but low sharpness usually won't.)
It's also possible to trace raster images into vector outlines, but this tends to only work well for "cartoon-like" images that already consist of relatively clean and simple lines. For photos, you're generally better off sticking with raster images and only embedding them into a vector drawing.