Slide Scanners

As I mentioned before, I really like to use slides for Astrophotography. Getting them digitized so that I could put them on my web pages has been a struggle. I believe I have finally found the solution: the new Hewlett-Packard PhotoSmart Photo Scanner. Costs about $500, allows slide scanning at 1200 and 2400 Dots Per Inch optical with 30 bit pixel depth (10-bits per color). When I first saw the specs on the HP web page, I knew they had a winner in both the price and performance area so I put one on order as soon as they said they were shipping.

Before I got the HP scanner, I took my slides to a local photo lab for digitization. They used a Nikon LS-1000 and I specified "no image processing" so that I would get a simple scan of the photo. This allowed me to work with the scanned image and determine the color density of the red, green and blue components of the image. This is handy for color correcting the image if a particular film's red, green and blue reciprocity failure curves are different.

I also recently sent my favorite Astrophoto slides to Kodak so they could make a "Kodak Photo CD". I just got the CD back. Again, I specified no image processing so that I would have just a simple scan.

So that means that I am now in a position to provide a simple comparison between scans obtained with the HP PhotoSmart Scanner, the Nikon LS-1000 Scanner and whatever Kodak uses to produce a Photo CD. I selected probably the most difficult slide I have taken, the three-hour exposure at f/6.3 of the Cone nebula. I cropped each image to approximately the same region about the Cone. Each image is 1200 DPI. Each of the three images immedately below are without any sort of "processing", i.e., they are simply scanned and presented as is. Remember, this is an extremely difficult test for these scanners and in no way represents their overall performance. The Cone nebula image is relatively dim against a dark background. To be able to pull *any* discernable image out is a testament to the sophistication of these scanners.

Nikon LS-1000

Kodak Photo CD

HP PhotoSmart Scanner

It looks like the Nikon scanner produces a pretty good image. The Kodak Photo CD scan appears to have a little less detail than the Nikon scan. The HP PhotoSmart scan has about the same detail as the Kodak Photo CD but there are some striations visible associated with the scan sweeps. (These can be removed by "processing" the image during scan. Recall that for the above test, pre-processing was disallowed so the results of "raw" image scans could be compared.)

HP PhotoSmart Scan with "Processing"

When I send a slide off to some photo lab, I have to specify "no processing" because you never know what they will do to an astrophotograph. Same problem that one has with print film. BUT, if I own the scanner then I can allow some "processing".

The HP scanner reads the slide at relatively low resolution then displays the image on the screen. You are then able to invoke some "processing" tools that allow you to crop the image and adjust brightness, contrast, color saturation, etc., before the actual image scan. You can see the results of your adjustments on the screen and, when you are happy, you can allow the final scan. This next image is the final scan after some "processing" adjustments.

HP PhotoSmart Scan with image processing.


After you have the above image, you are free to make further adjustments to the image using some third-party photo image processing system. The image below was created from the image above by adjusting brightness, contrast, etc. This image begins to look like my slide. Although nothing seems quite as good as an original slide, the HP PhotoSmart Scanner appears to capture the image as well as anything else I've tried.

Copyright 1997, 1998, 1999, 2000 Howard C. Anderson