Many people ask what determines the quality of their scans with scanR. There are many factors but they can be summarized into these groups: camera quality, user behavior and physical environment. This post focuses how these factors impact the clarity of the text in your document scans.
For document scanning, the goal is to produce as much usable information as possible. The raw resolution of the camera and distance from the document determines the effective resolution of your scan. This megapixel to DPI conversion chart provides the math. If you have a 1.3 megapixel camera, you can capture a 4.3" x 3.4" document at 300 DPI, which is the standard resolution for high-quality photographs and professional print production. Faxed documents are typically 100 DPI, so a 1.3 megapixel could capture a 12.9" x 10.2" document and have fax resolution.
These numbers assume that your camera captures the full document edge-to-edge without any border, or wasted space. Although it is theorectically possible to capture only 4.3" x 3.4" of a document to produce a 300 DPI scan, the lenses on most camera phones will not focus that closely. Most 1.3 megapixel camera phones cannot focus more closely than about 12" from the document, and as a result capture a full page at just above 100 DPI. Many 2.0 megapixel camera phones and nearly all digital cameras have auto-focus lenses that will allow you to get closer to your document.
scanR recommends that you capture the full page with no border around your document. For most camera phones, this will ensure that you are not too close to the document. You may have to turn your camera 90 degrees to find the direction that captures the greatest amount the document. Try a few distances and orientations to learn what works best for your camera. You will find if you get too close, the image will be blurry and if you're too far away, the text will be too small.
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