This information is obsolete; the format is dead. We're leaving this on the web only for archival purposes.

Publishing FlashPix

by Philip Greenspun for photo.net.

(Note: Be sure to look at my FlashPix reference images, which are presented on a separate page so that those who haven't yet loaded the plug-in aren't annoyed by dialog boxes)

I wrote this document in July of 1997. Since then, some of the information has become obsolete. Notably, Hewlett-Packard has stopped distributing software in a simple manner (they do have some software but I haven't figured out what it does and they say that it will expire after 45 days). If you just want a PhotoShop plug-in, visit http://livepicture.com

FlashPix is an imaging format that lets you publish extremely high resolution images over the Internet. Readers of your site, however, wait only for the bits that they need.

For example, suppose that you are publishing a 4000x6000 ProPhotoCD scan. Uncompressed, this is a 72 MB file. After typical JPEGing, you'd still have a 7 MB file. This would take at least 20 minutes to download via a 56 KB modem. And if your reader wants to make a high-quality print at home, that's how long he will wait for the bits. But if the reader is viewing the image on a 1000x768 pixel display, he will never wait for more than 1000x768 pixels to download.

There are some other interesting things about FlashPix from a Web publisher's point of view, but I've written about them already in my scanning guide and my book on Web publishing. This document concentrates on the mechanics of getting a Flash image onto your Web site.

The Short Answer

The Long Answer

Now that you can let readers zoom way in on your images, you have to think a lot more about your original image quality and the way that you are scanning images.

High-Resolution Photography

Almost any image looks good if you don't enlarge it too much. That's the secret of the latest digital cameras and disposable cameras: most people never see the image larger than 4x6". If they enlarged it to 16x20" and then stuck their nose up against it, they'd be very disappointed. But they don't because it would take a week and $50 in lab fees. With FlashPix, you're enabling people to view images at effective enlargements even larger than 16x20". In a couple of minutes. For free. And they probably won't change their viewing position since they are sitting in a chair in front of the computer monitor.

The good news is that modern film is very very good. You can get 100 lines/mm resolution out of almost any film these days. lines/mm in the analog world means that you can resolve a pattern of alternating black and white lines, with N black lines/mm (only the black lines are counted). Using a caveman conversion to digital, that's 200 pixels/mm (one for the black line, one for the white).

The bad news is that, even if you had a lens capable of resolving 100 lines/mm, by the time you convolved its response with the response of some 100 line/mm film, you'd have only about 70 lines/mm in your picture.

The worse news is that you probably won't be able to find a lens capable of resolving 100 lines/mm. 50 is more typical of a prime (non-zoom) Nikon or Canon 35mm lens.

The even worse news is that lens resolution falls off in the corners and edges of the frame, the precise areas where a curious viewer is likely to be poking around.

I could spend a lot of time filling in the technical details that I've elided above, e.g., that resolution numbers vary by factors of 2 or 3 depending on the contrast of the target. But we've all got Web sites maintained so I'll keep it short and concentrate on bottom line advice.

Kodak Was Right

When Kodak limited regular PhotoCD to 2000x3000 pixels, they weren't cheating you out of the rest of your bits. Unless you have a tripod-mounted prime lens with Royal Gold 25 film, a 35mm negative does not contain much pictorially useful information beyond 2000x3000 pixels. With most equipment, you're lucky to get 50 reasonably contrasty lines/mm over the standard 24x36mm frame of a 35mm camera. That corresponds to 2400x3600 pixels. Of course, you're still somewhat better off with a higher resolution scan because at least then the convolution with the response of the scanning system doesn't further degrade the resolution you captured on film. But going to a 4000x6000 pixel ProPhotoCD scan for a 35mm original probably won't open up the dramatic vistas for which you'd hoped.

Conventional Wisdom is Wrong

With modern films, super electronic bodies, and millions of dollars of TV advertising behind them, it would seem that the 35mm SLR is the right camera for almost everything. That's probably true if what you want to do is take aesthetically pleasing pictures and blow them up to modest sizes and not view those modest enlargements from too close. I'm as fond of my Canon EOS system as the next photographer, but if I want to really impress someone with a deeply zoomable FlashPix, it isn't the right technology.

Before discussing the right technology, it is worth taking a moment to think about how to get the most out of a standard 35mm SLR system. Here are some tips:

The Right Stuff to Begin With

My friend Ted grew this Dahlia flower on his Cambridge condo's terrace You need a large-format original. A large format camera uses sheet film in sizes of 4x5", 5x7", and 8x10" (a few films are made in 11x14" sheets as well). I've written a bit about view cameras in What Camera Should I Buy?. Suffice it to say that the are not especially convenient to use. You would be lucky to get one good image/hour working with a view camera. Loading film is a hassle also, unless you are using a 4x5" camera and buy Fuji Quickload or Kodak Readyload film. Finally, scanning will be extremely expensive unless you use 4x5", the maximum size original that will fit into a Kodak ProPhotoCD scanner.

On the plus side, view cameras are easy to rent and relatively cheap to buy. The latest and greatest view camera lenses are reasonably high resolution. Surprisingly, they aren't as good in terms of lines/mm as a Canon or Nikon lens, but they don't need to be. You aren't enlarging as much.

Caveat: you must verify your view camera's alignment with a Zig-Align tool (available from zigalign@compuserve.com for about $50). This is a marvelously simple pair of mirrors. One of them fits into the camera back like a film holder. The other mirror fits on the lens board and has a small hole in the middle. If you throw a penlight into the bellows and look through the mirror on the lensboard, you'll see a infinite regression of concentric circles when the mirrors are perfectly parallel. If you don't align your view camera, especially a wooden one, you'll probably get enough unsharpness from focus variation that you'd have been better off using a rigid medium format camera (e.g., Hasselblad).

ISO 100 film is fine in a view camera. I am extremely lazy so I like to use Kodak Pro-100 Readyload. It is a color negative film, so it tolerates minor exposure errors well and never gets too dense for a CCD scanner like the one used to make Kodak ProPhotoCDs. If you use the Kodak Readyload back, exposures are reliable (though I've created quite a few "black bear in a cave" pictures trying to use Kodak Readyloads, mostly in the Polaroid 545 holder which allegedly works but not for me).

A good film for landscapes is Fuji Velvia, ISO 50, available in Fuji Quickload. Bracket your exposures, though, because Velvia doesn't have too much scale (ability to represent a lot of shades from black to white). Many people prefer Velvia slightly overexposed (especially if you are scanning with a CCD) so bracketing +1/2 and +1 f-stops from the meter's recommendation might be wise.

The Semi-Right Stuff to Begin With

If you aren't willing or able to lug around a view camera, you can get at least one extra level of zoomability with a medium format camera. The most commonly rentable medium format camera is the Hasselblad, which exposes 6x6cm images on 120 film. I wrote a review of the Rollei 6008, which is a similar camera. You might also want to check the photo.net review of the Mamiya 6, a simpler alternative (the Mamiya 7 is also a nice camera that takes 6x7cm negatives).

The highest resolution color film in 120 is Ektar 25 (PHR-120), the same film sold as "Royal Gold 25" for 35mm cameras. It is a color negative film and therefore scans very nicely to PhotoCD. For landscapes, I would consider this or possibly Fuji Velvia. For photographing people, I like the subdued palette of Fuji NPS.

Scanning

The cheapest and easiest way to get a good high resolution scan is to go to one of my favorite PhotoCD labs and say "please make me a ProPhotoCD". That gets you 4000x6000 pixels for $15-25. Another approach is to go to a drum scanning house and say "please make me the highest resolution file that you can." I had a couple of 590 MB files produced this way. They cost almost $1000 each at Graphics Express in Boston. I wasn't very happy with the file gamma and thought that the image had been overly sharpened (drum scanners have built-in hardware to do unsharp masking). Moreover, it is tough to find a combination of hardware and software that can convert the full 590 MB files into FlashPix. My latest approach is getting 600 MB files made at The Photo Lab, a drum scanning house that is also a ProPhotoCD shop and therefore more experienced with the needs of Web publishers. They are giving me 600 MB files with little or not sharpening for about $300 each. You'll want to look at my FlashPix reference images to decide if the extra bucks are worth it over ProPhotoCD.
Text and pictures copyright 1991-1997 Philip Greenspun.
philg@mit.edu