Wednesday, July 17, 2013

iPhone versus Camera Document Scan

Comparison of Sony and iPhone document imagesLast time I related my experience using Shoebox from Ancestry, the new smart phone app from Ancestry.com. It turns your cell phone into a portable scanner. While marketed primarily as a photograph scanner, I tested it as a document scanner. Today I’ll continue my evaluation with a comparison of photograph quality.

Because photograph files are often compressed to save size, I worried that Shoebox might compress the file uploaded to Ancestry.com. I checked and found that the copy of the photo on Ancestry.com was exactly the same as the iPhone original.

Next I compared the quality of the cell phone photos to the higher resolution photos from my 14 megapixel Sony. What I found surprised me to a degree. As expected, the Sony photos were pristine clear, colors matched the original documents, there was no perspective distortion, and no other distortions that I could discern. (More on that later.)

Oops. As I inspected the Sony photograph, I noticed I had forgotten about a tiny problem with my Sony. There is a swath along the left margin that is often out of focus. I have to watch carefully for this in archives, as I sometimes return home and find I can't read important details along that edge. Blame the lens. Consumer cameras have cheap lens with these sorts of subtle imperfections. I read recently (sorry, no citation) that lens quality has gone down in recent years offsetting improvements in resolution. Today's cameras give no clearer photographs than the lower resolution cameras of a couple years ago.

The iPhone photos, on the other hand, had several problems. The first thing I noticed was color. The slight yellow-brown of the document had become orange. Technically speaking, the iPhone had automatically increased color saturation. For consumer photography, this has the pleasing affect of bringing out the blue in the sky, the green of the forest, and the red of the sunset. For documents, it is unsound.

Next I noticed that writing at the edges of the document had been clipped off. In subsequent attempts I learned to be more careful, positioning the corner crosshairs a little off the document.

Next I noticed that the iPhone had introduced banding, visible like parallel gray shadows running up and down the document.

Placed side-by-side, the iPhone image was taller than the Sony. I didn’t think to measure the document itself, so I can’t tell you which one squished/stretched the image.

Zooming in to see document details, I felt the iPhone did as well as the Sony. Unfortunately, the iPhone uses higher jpeg compression. While the iPhone’s files were quite a bit smaller than the Sony’s, the iPhone jpegs had bigger halos around the letters of the document. The halos are not as visible in consumer photography, but for legibility of historical documents, jpeg compression is problematic and the higher the compression, the worse it gets.

As to be expected, Shoebox cropping does waste some camera pixels. Mathematically, I know it also produces minute blurring. Practically, there is no trace that it has occurred. However, you should always  center the camera exactly over the center of the document and try to square up the document before taking the picture.

I had one document that, try as I would, I could not get the iPhone to focus.

Finally, I had photographed a grid pattern on the copy stand. Here I could see that the iPhone lens produced greater barrel distortion than the Sony.

So what conclusions did I come to?

  • The first thing I need to do is throw away the Sony. That lens aberration has got to go.
  • Neither camera produced results as good as a flatbed scanner. For  important documents (and photos, for that matter), use a scanner. Duh. I should have used the scanners built into the copy machines at the Archives. 
  • For those times that scanners are not available, try a camera with a decent lens. A cheap standalone or cell phone cameras should be your last choice, but can produce acceptable results.

As this is a Shoebox review, I should conclude with a conclusion about it. I’ll save that for tomorrow’s wrap.

4 comments:

  1. I know your focus on this commentary was for doing documents, but recently I was scanning photos with a flatbed and the results it produced were wholly unacceptable. It distorted all of the darker regions to a monochrome blob that did not produce a true copy. Is there something wrong with my scanner, or is there some sort of setting I'm unaware of? I was excited about Shoebox purely because of this, even though the camera on my phone is very poor. It's either a ruined copy or a blurry copy until I can figure out my scanner.

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  2. Don't throw away your Sony! Assuming it's a DSLR, go to a site that sells used gear (such as KEH.com) and get some Minolta lenses. The quality of Minolta glass is outstanding, and the Sony DSLR uses the Minolta mounts. (Which is not surprising, since Somy bought Minolta's camera operations.)

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  3. As someone who manages digitization at an archives, this is a useful comparison of the pros and cons of different cameras for documents. It's kind of tricky as I'm learning right now, advancing from flatbed and microfilm scanning to cameras (especially for full color). Best case scenario is something like this.

    Heather, I would check your scanner. I'm still using one that's almost a decade old at home with good results. There's some scanning tips from the Library of Congress that might help. The whole site, digitalpreservation.gov/personalarchiving, is one I recommend frequently to people interested in preserving their stuff.

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  4. I am wondering if photographing smaller portions of a document and then stitching them together with a program like Microsoft's Image Composit Editor would produce better results. Has anyone tried doing this?

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