How many megapixels are enough?

Since the advent of digital photography there has been a debate about how many megapixels are enough. As usual, it depends what your trying to do - sending a picture via email needs fewer megapixels than making a 24" x 30" print. I decided to post an unprocessed image to give people an idea of what is possible with medium format film. This image was taken with a Pentax 6x7 camera and 55mm F4 lens using Fuji Astia 100F slide film. It was scanned at 4000 DPI with a Microtek 120TF using Lasersoft Silverfast, and then stored at JPEG quality 8. The image above has been down-rezzed to under 1 megapixel.

The full size image, about 94 megapixels, compressed down to 33 MB using JPG qualty 8. You can download it by clicking here. Please be aware - this will take a *long* time to download over a dialup connection! This image has not been sharpened for final printing - you can try 88%, 3.4 pixels, 2 levels as a starting point. You're welcome to download the file, bring it up in Photoshop and play around with it, but you are not permitted to use it for commercial purposes.

Many things change when you're working with 90 megapixel images. You need a lot more memory, disk space, and CPU, obviously. You don't need to worry so much about JPEG artifacts - I really don't notice much difference between the original and the JPEG but the file sizes are substantially different. A tiff of this scan would be about 270MB. A quality 10 JPG is 115 MB and the quality 8 JPG is 33MB. I usually use JPG quality 10 and make 24"x36" prints with no problems.