For Image Science, scanning is a core service, and we have invested considerable time developing processes to produce the best possible scans.
We believe a truly fine print is always the ultimate goal of scanning. This means we scan a little differently to most other services, and you may initially find that your files look a little flat. There is a good reason for this, and of course our scans can be made to look exactly like other scans from labs etc. However, we go out of our way to give you maximum detail in your scans, so you can make the best prints possible.
The basic difference is that our scan is a more 'raw' scan, which is colour balanced but has not yet had the final black and white points set, and is giving you all the data the scanner can pull from the transparency (i.e. the full dynamic range). Whereas other services often provide you with a scan that is essentially 'finished'. We would argue that our method is better as it allows you more flexibility in setting the points. In the case of 'finished' scans, somebody has already made the decision for you and clipped some pixels to pure black and pure white, which means you probably have lost detail. Their approach offers more initial bang, ours offers better fine printing options.
Our approach is for maximum detail - giving maximum flexibility. To achieve the same result with our scans as theirs, you could just use the Photoshop levels command to shift the black and white points in a little. However, a better way to do this would be to use an S curve, to increase contrast while not losing any detail. If you want us to provide clipped scans we can of course do this, but you are potentially limiting your options.
If you have a low key photograph say (i.e. the majority of the tones in the image are dark), that relies on good shadow detail, then their approach of providing clipped scans will be a big mistake. Same goes for highlights, of course. The key thing is that our approach is to give you the best chance of getting all the detail off the slide, while theirs is to give you a scan you can immediately use. Both have their benefits, but if you're in photography and you're interested in print quality, you should pretty much always be requesting unclipped scans.