Canon's CanoScan FS4000

Updated Feb 28, 2002, Page 2, ©2001 by Dale Cotton, all rights reserved

Colour and Tonal Gradations

Besides 4000 ppi, the other big number associated with the FS4000 is its bit depth, which is all about colour and tone.

Accuracy

No amount of bit depth is going to do us any good, however, if the scanner has any problem with colour accuracy. Neg film has an orange tint that varies slightly from manufacturer to manufacturer. This tint must be exactly cancelled out before the true colours can be recovered. The FS4000 handles this much better than my previous S20, saving me greatly in post-processing time. More than half my neg film images need no adjustment to achieve the same level of verisimilitude I expect from transparency film.

(Added Feb 28:) A fair percent have varying degrees of purple cast, esp. low contrast scenes. I've noticed a similar magenta cast on a scan in Norman Koren's review. This is quite correctable in editing software. I don't know if any other scanners or scanning software can do any better or not; my understanding is that most scanners have one problem or another with neg film colour.

The Imaging Resource review demonstrates the accuracy of the FS4000's transparency film colour handling via its Q60 testing.

The FS4000's FilmGet interface also provides an optional Color Matching setting. It does not provide colour space choices, but that's because it doesn't need them. Because the raw image file is imported into Photoshop or whatever software you use via TWAIN, your choice of colour spaces is assigned at that time.

Tonal Gradations

Now let's get back to 42 bits. Suppose you are taking a close up photo of a white hen's egg on a plate with light coming from a window to the left. As you look at the egg before clicking the shutter release, the brightly lit side of the egg gradually darkens to complete shadow. There are no bands of different shades of grey; there is simply a smooth, gradual change from white to dark grey. (Smooth except for the egg shell's slightly rough texture.) This transition between lightness and darkness is called tonal gradation. 42-bit colour suggests the potential for wonderful tonal gradations. Counting the colours in the following image fragment yields ~76,000 in 42-bit vs. ~39,000 in 24-bit. Unfortunately I can't show you the 42-bit version due to file format limitations.

Figure 1. Hair crop used for colour counting.

Do you need 42-bit colour?

One advantage of greater bit depth is the colour and tonal gradations just mentioned. The second reason to be concerned about bit depth is Dmax. We've all had the experience of being outdoors on a glaringly bright sunny day. Shadows seem an impenetrable, inky black. If we hold a hand up to block out the sun, we can quickly make out more detail in the shadows. In essence, Dmax measures how well a scanner can extract detail from the shadows of a transparency on a scale of 0 to 4.

Of course just because a manufacturer claims 4000 ppi or 42-bits doesn't guarrantee the results will back up those claims. Other reviews contain sample images that you can download for yourself. My own results fully support those of other reviewers: the FS4000 does have superb resolution and it does have significantly more Dmax than previous generation, 12-bit, scanners. (Update Feb 28:) Initially, Canon's press releases for the FS4000 claimed a Dmax of an extremely modest 3.4. It later turned out that this was an error from the marketing wing of Canon and the new figure is the theoretical maximum for 14-bit scans of 4.2 - the same as all other manufacturers are claiming. (Let's hope no-one got fired!)

Neg film

For neg film not every image will noticeably benefit, but many will. A major difference in larger bit depths is the greater latitude for software adjustments to the image in post-processing. For example, suppose you have an image you value but the blue sky is so pale it's almost white. The greater the bit depth the better the chance that the sky will retain colour. Ditto for shadow detail.

Figure 2. S20 scan vs. Figure 3. FS4000. Click on either crop to view entire frame.