Forensic Imaging and RAW Files
Written by Steve Scarborough   
 
 
PREVAILING OPINION suggests that RAW files were tailor-made for forensics and law enforcement. However, this issue should be examined closely in order to fully understand RAW files and to prevent a forensic-imaging system from becoming bogged down due to the time and man-hours necessary to process RAW files. After taking a closer look, one may find the comprehensive value of RAW for forensics is somewhat overestimated.
 
Crime-scene photographers and forensic-laboratory analysts use some form of RAW files during the course of their duties. It would be naïve for forensic photographers to shoot in RAW and not have the proper scientific support. Forensic photographers should not succumb to pressure to shoot everything in RAW.
 
RAW sensor data
 
A RAW file is a data file of information and is not a photo until it is processed. RAW files are not image files like a JPEG or TIFF. Actually, a JPEG image came from the RAW sensor data in the camera and was automatically converted to an image file. RAW files are used to transfer data to your computer before processing and converting into picture files.
 
Unfortunately, there is no standard RAW file; they are nonstandard proprietary formats that vary between manufacturers and even within a manufacturer’s individual lines of cameras. There is also no standard for RAW files within the industry. This is important for forensics because it is not known if these files will be accessible from the archive five or ten years down the road. This is particularly significant when one considers the fact that in the forensic community, it is often important for images to be kept for decades.
 
Much is said about the value of being able to process a RAW file. However, it seems that every RAW file opener processes an image a little bit differently. There is no absolute standard for RAW processors. It is not known if the future RAW processors will be able to handle the current RAW files in the forensic archive. An agency will have to convert these to TIFF or JPEG anyway to avoid this problem. Additionally, any post-processing of the RAW file is not saved with the RAW file. A RAW file cannot be overwritten, so the post-processing must be saved as new file.
 
TIFF images are accepted as quality images within the forensic community. The quality issue regarding JPEG images deals with the compression process. Avoiding this issue is actually simple: save the original JPEG file and work on a copy. The original photograph in JPEG will not degrade if the original JPEG is kept pristine and never opened or uncompressed and recompressed. Some forensic digital imaging software programs automatically save the original file and restrict image processing to copies.
 
Normally, crime-scene and laboratory analysts save RAW files and archive them, but view the JPEGs and work with those for crime-scene documentation. JPEGs are accepted as an adequate format for crime-scene and evidence documentation. This does not conflict with any forensic requirements. Therefore, lossy compression formats can be used for documentation purposes and lossless formats, such as TIFF, can be used for images used for analytical purposes.
 
There has been debate in the forensic community about the best evidence, and some state that since a RAW file is in the purest form, it is essentially a digital negative. This is not true. The RAW file is not a universally viewable image. It is a string of unprocessed data from the pixels in the camera. For all the reasons stated in this article, a RAW file is not a digital negative.
 
Additionally, the Scientific Working Group on Imaging Technology (SWGIT) recommends maintaining an archive image, and defines the archive image as “…either the primary or original image stored on media suitable for long-term storage.” The primary image is defined as “…the first instance in which an image is recorded onto any media that is a separate, identifiable object or objects. Examples include a digital image recorded on a flash card…” In other words, an archive image is an exact copy of what the camera recorded onto its original media. Under this definition, both a TIFF and a JPEG image, if archived properly, would fall under this guideline.
 
Quality
 
The value in a RAW file is in the ability to pre-process the image to obtain the best exposure. Note that this statement specifies exposure, not quality. There is no quality value or higher resolution value in a RAW file.
 
There have been some published quality comparisons of JPEG and RAW images. These reports should be analyzed with great skepticism. Based upon testing, the reports that show some difference in quality were probably “Photoshopped,” or manipulated, to comply with the pre-determined conclusions of the photographer, thus promoting RAW files. Do not take these previous results at face value. Law-enforcement photographers should be encouraged to conduct their own tests. The author’s own extensive testing shows no quality difference in a RAW image and a JPEG image shot at the same time with the same exposure settings. Only after JPEGs have been opened, edited, closed and reopened was any quality difference noticeable.
 
To quote photographer Steve Bohne, “No, RAW files will not be sharper than the JPEG files, and anyone who says they will doesn’t know what they’re talking about.”
 
Advantages of RAW for forensics
 
RAW files provide the ability to adjust color, white balance, and contrast settings with finer control of these functions. RAW files will allow a forensic specialist to adjust the image to obtain the best possible representation of that scene or evidence image for analysis. This process is especially helpful if the image is right on the edge of clarity and needs just the right processing to improve it for analysis.
 
In order to take advantage of a RAW file, the file must be processed. Exposure and color is adjusted using a processing program. The RAW data file still needs to be converted to a workable image file such as a TIFF for distribution, analysis, and advanced printing. You cannot simply e-mail a RAW file, nor can you embed a RAW file in your documentation notes or reports. In a forensic or police setting, this processing step takes up valuable man-hours and requires additional training. This is training time and funding that might be better utilized in training the photographers to better control the camera settings when initially taking the photos. A workflow that calls for processing of all RAW files is just not practical or fiscally responsible in a law-enforcement environment.
 
If a law-enforcement agency decides to capture photos using the RAW setting, the best forensic workflow would be to take RAW files for all comparative analysis or highly sensitive cases, and capture JPEG files for all others such as location and demonstrative photos.
 
A standard forensic workflow for the RAW images would be to convert all of the RAW files to TIFF images and save the RAW and original TIFF files within the system. Then, use those high quality TIFF images within the normal course of analysis, documentation, and distribution. Then, if necessary—and only if necessary—retrieve the RAW files and process them within a RAW-file program.
 
While RAW files can be valuable in law-enforcement photography and forensics, they should be used in a measured and limited process—in special circumstances—to preserve an efficient and cost effective forensic photographic system.
 
About the Author
 
Steve Scarborough has more than 29 years experience in law enforcement with Las Vegas Metropolitan Police Department as a forensic scientist. He recently retired and currently works as a digital-imaging consultant, contracting with Mideo Systems. During the last few years, Scarborough has given lectures and presentations on digital imaging around the country. He can be reached by e-mail at: This e-mail address is being protected from spam bots, you need JavaScript enabled to view it Or you can reach him by phone at: 702-334-6667

 

ORIGINALLY PUBLISHED:
"Forensic Imaging and RAW Files," written by Steve Scarborough
July-August 2010 (Volume 8, Number 4)
Evidence Technology Magazine
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