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Digitizing Three-dimensional Objects (D4.d)

Definition

Direct capture of 3-D objects must be accomplished by using a camera. You may use a digital camera for direct capture or you may use a film camera and digitize the results with a scanner. If you have access to a digital SLR camera with at least 10 MP (megapixels) of optical resolution then you will probably want to use that device for your digital capturing because of the inherent convenience of immediately capturing your image in digital format. Otherwise, even using a cheap 35 mm. conventional film camera will generate a high-quality image that you can then run through a scanner.

Digital Camera Resolution

Be aware that digital camera specifications usually give resolution in terms of interpolated resolution, not optical resolution. Interpolated resolution figures should be ignored. You must be sure to use only the optical resolution of a digital camera when deciding if it will be adequate for serious digitization. Cameras with less than 5 MP of optical resolution are not recommended.

Digital Camera Shooting Tips

  • Provide lots of ambient light, but do not use flash for the lighting.

  • Focus is seldom a problem with a flatbed scanner, but with a digital camera it es. Ensure that when viewed at 100%, the image is well focused. If not, reshoot it.

  • For digitizing most 3-D objects, it is not practical to capture a grayscale or color profile target along with the object itself.

  • Use macro settings or a lens for close up photography.

Camera Setup

Pixel size should be set as high as possible, but no lower than 2560 x 1920 (5 MP) and the Quality setting should be set for "high," "fine, or "super fine" depending on your camera's labeling terminology. Turn off automatic date and time stamping of the image. The date and time are preserved by most digital cameras by automatically embedding them into headers in the file itself.

Meeting the desired archival resolution of 4000 pixels on the long side is hard to achieve with consumer-grade digital cameras today (Feb. 2007), but try to get as close to this number as your camera will allow and position your camera as close to the object as possible. Do not up-sample (increase the number of pixels) of an image using photo editing software just to get more pixels. That doesn't improve the quality.

Digital Camera Storage Format

It is preferable to use a camera that stores its images in a native "raw" format or in the standard "TIFF" format, but most cameras store their images as JPEG files, which means that from the very start, the image is undergoing some lossy compression. If your camera stores images as JPEG files, there are a couple of things you can do to minimize the degrading effects that JPEG compression can have on the image.

  • Set the resolution on the camera to the maximum value.

  • Select the lowest degree of compression offered by the camera.

  • Once the image is transferred to a computer, convert the JPEG image to a lossless format such as TIFF.

Specifications

View the diagram:  Specifications for Digitizing Three-dimensional Objects.

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(Reviewed: September 27, 2008)