The Benefits of Camera RAW Data
Posted by Shannon Crawford on 11 April 2013 09:44 AM
All digital camera RAW files are stored in a "read only" format that includes the original data for the light that was “sensed” by the photo receptors on the imaging sensor. In addition, the photoreceptors are covered by a Color Filter Array that allows each photoreceptor to capture only one light value, where the value is filtered either by a red filter, a green filter or a blue filter. The missing red, green and/or blue values for each picture element or pixel are created using the filtered light values of the surrounding neighbor photoreceptors using a standard technique commonly referred to as a Bayer pattern. As a result of this color interpolation process, each pixel will have a Red (R), Green (G) and Blue (B) value. In the case of JPG and TIF files, the conversion of light data to RGB values is done inside the camera whereas the conversion of light data in camera RAW files is done at the computer.
In addition, the imaging sensors for all digital cameras have a dynamic range that allows the sensor to distinguish between 4,096 shades or 16,384 shades using (12-bits or 14-bits, respectively) of light sensitivity, depending upon the make/model of the digital camera as well as how the camera is configured (typically a menu setting).
When JPG and/or TIF images are created by a digital camera, the camera software processes the data from the imaging sensor inside the camera, and the light values above the standard 256 values is discarded (original data vales are permanently lost). When camera RAW files are converted using a program such as Adobe Photoshop, all 4,096 or 16,384 values can be used, thus providing a significantly higher contrast and dynamic range within the image and the original values from the imaging sensor are always available.
NOTE: When storing an image using 16-bit color values or using a 16-bit color setting on a flatbed scanner, each pixel can have a total of only 512 color values. The first byte (or first set of 8-bit color values) represents the shadows – aka the 256 dark grayscale values starting with the value 0 or black through a midtone value of 255. The second byte (or second set of 8-bit color values) represents the highlights – aka the 256 lightest grayscale values starting with the midtone value of 256 through the value 511 or white. The distinction between 8- and 16-bits (256 shades/512 shades, respectively) and 12- or 14-bits (4,096/16,384 shades, respectively) can make the difference between not being able to capture a poor quality latent print and being able to capture, process and identify a faint ninhydrin print on a printed background, such as a check or money order, or a poor quality latent print developed using a fluorescent dye stain visualized using an laser or other alternate light source. Furthermore, this is the reason why images with color backgrounds, such as latent prints developed using ninhydrin on a check or money order, can be processed far more successfully when captured with a digital camera than with a flatbed scanner. In addition, flatbed scanners have only one light value, so the sensitivity between RGB values is extremely limited, which also causes problems when trying to suppress backgrounds that interfere with the visualization of evidence, such as latent prints.
The Microsoft Windows operating system is based on 8-bits to a byte, so 16-bits would be stored as two bytes. Since Windows does not know how to read (aka parse) 12- or 14-bit color values, Windows cannot display the image and you typically cannot even see the thumbnail images in Windows Explore unless you have downloaded and installed the Nikon Codec. (Instead of the thumbnail, you typically see a picture icon with the letters NEF overlaid on top of the icon.) Once you open the original NEF (Nikon Electronic File format aka camera RAW file format) file using the Adobe Photoshop converter, the file data is converted into image data using the standard Microsoft Windows O/S 8-bit format or 16-bit format, so the processing information (density and color values modified in the Adobe Photoshop camera RAW converter) cannot be written back to the original file – again, Windows does not know how to convert the 8- or 16-bit data back to 12- or 14-bits, so a child file (aka sidecar file) is spawned during the conversion process to store the image adjustments and corrections. This newly created file uses the exact same name as the parent (original) file with the extension of .XMP, and contains only the conversion data (the settings and parameters for all of the parameters available in the Adobe Camera RAW Converter regardless of whether or not the value was changed during the conversion process) – the XMP file does not contain any picture (pixel) data.
After you have completed the desired processing in Adobe Photoshop successfully, you are prompted to save the processed file, which typically uses the same filename as the parent but with a different file extension (file format such as TIF). Since 16-bit images require two bytes for every pixel, it is recommended that mode of the processed image be saved as an 8-bit grayscale because the evaluation of the processed image is done by the human eye, which can only detect somewhere between 64 shades of gray and 128 shades of gray, depending upon which expert you ask. However, the additional dynamic range during image processing is critical because the computer can distinguish the difference between color values in excess of 16.7 million color values.
With Digital Workplace, every time you send an image to Photoshop for processing using the option of Process as Raw ..., you are starting with the original RAW, unprocessed, 12- or 14-bit data that was originally “sensed” by the photo receptors on the imaging sensor and saved by the digital camera.
NOTE: It is not necessary to save the XMP (sidecar) file because all of the camera RAW settings are embedded in the processed image file's metadata. Saving the XMP file therefore is redundant and can create problems as it becomes yet one more file that must be managed along with the original image file and the processed image file. More importantly, this becomes a secondary file that you must be able to explain in the courtroom; and since the data is not stored in a simple, easy-to-read format like the data that is saved in the file metadata, it can be challenging to explain what each setting means. Furthermore, in the event that you want to reprocess the original file, you want to begin with the original data from the imaging sensor … not limited, converted data.
Once again, there are two primary benefits of using a camera RAW file format:
(1) The files are a “read only” file format and cannot be manipulated or overwritten with modified image data (thus keeping the courts very happy); and
(2) You can correct literally every photographic parameter and setting (temperature, tint, while balance, exposure, contrast, brightness, so on and so forth).
About the only issue that you cannot correct is the image focus. But you can "enhance" the focus and minimize some of the depth of field issues using the clarity and vibrancy settings using the original camera raw data.