With manual or automatic 35mm film, the film is run through a chemical process to develop the negative. With digital media, or in the York County/City of Poquoson Sheriff's Office's case with CF cards, the images are run through a software program to achieve the same results. In 35mm film photography, law enforcement is able to modify the picture size and adjust the color, brightness and contrast through varying levels of exposure. With digital images, photographers use computer software to accomplish similar results. With almost all digital images and any software application for image processing, photographers should limit their processes to size, resolution, color, brightness and contrast adjustments. Enhancement techniques may be used for digital images containing fingerprints or other impression evidence.
Processing or enhancement tools
Processing software is kind of like cars — a person can either opt for the Yugo or the Cadillac. Depending on the size of an agency and the number of crime scene images photographers take, an agency may select one of the mega auto digital processor units such as those found at one-hour processing shops. For small to modest-sized agencies, a stand-alone computer and printer may be all that's required to process images.
There are many software programs well suited to law enforcement digital image processing, but when selecting software, be sure the program has the ability to keep a history log file. The image software most computers come bundled with is often only suitable for image viewing.
Sometimes more than one software tool may be necessary. The York County/City of Poquoson Sheriff's Office, for instance, uses a combination of purchased software and bundled software that came with its cameras and printer.
York County officials use PhotoShop CS for their image processing requirements. PhotoShop is arguably the premier in image processing and enhancement software for digital imaging because there are a number of tools available through PhotoShop that can be used for digital imaging processing as well as video image enhancement. The capabilities of such tools are:
- The ability to add on software programs (plug-ins) that will run through PhotoShop. These individual programs, such as "More Hits Pattern Removal" and "Software and Calibration Utilities," allow users to print images in a 1:1 format — a useful tool for latent fingerprint images. Some of these plug-ins are available as free downloads while some must be purchased.
- The ability to read and process images using the proprietary .RAW image formats of most digital cameras and then convert those images to any number of common image formats. PhotoShop also will read the camera's Meta Data or Exif data to allow users to see what camera and flash settings were used when the image was taken.
- Color inversion, sharpening and gray scale capabilities allow operators to process photographed fingerprint images of fluorescent or white powders on a black background and convert them to black fingerprint images on white. The "un-sharp mask" filter enables users to sharpen fingerprint images that may be slightly out of focus.
- Court display production allows users to chart fingerprint identifications.
While numerous enhancements are possible, the York County/City of Poquoson Sheriff's Office limits its processing to image size, resolution, brightness, contrast and color corrections. Officers are able to use a tool called "curves" to fine-tune image exposure to underexposed images. "Curves" allows equal color adjustment across the full color spectrum.
The York County/City of Poquoson Sheriff's Office sizes its images to 5-by-7-inches (5x7) at a 266 dpi (dots per square inch) resolution. The department selected 266 dpi because it is considered "museum-grade" quality. All of the department's processes are logged in a history file within PhotoShop that can be printed as needed.
The most mundane tasks in PhotoShop can be automated to run automatically. The York County/City of Poquoson Sheriff's Office found this tool particularly useful when officers needed to change the image sizes of approximately 23,000 digital mugshot images for use in a new database.
Most digital cameras will come with a bundled image viewer or software programs. Some have PhotoShop LE (Limited Edition) or PhotoShop Elements, which allow users to perform most processing tasks. However, these programs typically lack the ability to add plug-ins and do not support .RAW camera file formats.