CLPEX Chat Board

Recently our lab has been asked if footwear evidence can be submitted for examination if it has been taken with a digital camera. Each time a department inquires or submits digital photography we try to explain the necessity for using traditional film methods, but are unsure ourselves if any further research has been conducted into the use of digital photography.

I was looking at the SWGIT footwear and photography guidelines and noticed it was dated 2003. In this edition the SWGIT committee references that digital photography is still not recommended pending further research into this topic.

Does anyone know of departments or individuals that have conducted research on the use of digital cameras for footwear evidence, in particular anyone associated with SWGIT? Some people have suggested various megapixel numbers, but has research been done to back any of this up?

I know that SWGTREAD has been drafting their guidlines but I don't think they have completed the guide for the forensic documentation and photography of footwear and tire impressions at the crime scene.

It is my understanding that for a digital image to equal the resolution of 100 ASA 35mm film it needs to be in the area of 20 mega-pixels, though I'm not aware of research to support that. I still encourage folks in the field to shoot examination quality photo's with 35mm. I don't care if they use digital for the scene overall photo's or location establishing photo's.

I know that SWGTREAD has been drafting their guidlines but I don't think they have completed the guide for the forensic documentation and photography of footwear and tire impressions at the crime scene.

It is my understanding that for a digital image to equal the resolution of 100 ASA 35mm film it needs to be in the area of 20 mega-pixels, though I'm not aware of research to support that. I still encourage folks in the field to shoot examination quality photo's with 35mm. I don't care if they use digital for the scene overall photo's or location establishing photo's.

Kelly,

I dont know if he is associated with SWIGIT or not, but George Reis is a great contact for questions related to digital imaging. He posts on here every so often to chime in about digital related questions.

My ears were burning.

There are many issues here. I'll try to address them all, but I may miss one or two.

The first one I want to address is the comparison of digital to film. This is the wrong approach. Instead, any method used to capture visual information should be judged as to whether it captures the necessary information, not if it is the same as, or better than film. There are so many factors, and so few objective tests that the film/digital comparison is unlikely to be settled in an on-line discussion anyway.

The question about moving from film to digital for footwear photography (or for anything else) should revolve around whether the quality is adequate, whether there are any court issues, if it is for an accredited lab - how it meets accreditation requirements, and whether it provides a benefit over current methods (that is, if there is a compelling reason to make the change).

Regarding quality, I have discussed this issue with footwear examiners, and have been told that the quality of digital footwear photography done properly exceeds their quality needs. I've also been told that poor quality film photography doesn't meet their needs. There are many factors involved in image quality from camera quality to lens quality to sharpness (focus, depth of field, camera movement, lens quality, resolution, etc.), lighting, exposure, etc. Remember also that one can always move their camera closer and take multiple, overlapping images to maximize resolution.

Regarding court issues. There really are none - the rules of evidence and case law are quite clear regarding digital imaging technology.

Regarding accreditation issues. These are also simple - one needs to utilize best practices, validate procedures and maintain good records. Digital technology doesn't change this, and it is easy to meet.

Regarding benefits. Depending on ones workflow, there can be a significant inprovement in efficiency and speed. For enhancement, I am not sure if an argument can be made regarding the differences in capabilities of enhancing (clarifying) original digital images over scanned film - but there may be a slight benefit. I would argue that better original images can come with digital - even if the camera is of modest quality because one can verify the image content, exposure and sharpness in the field with digital. With a good quality digital camera, this becomes even more significant. Cost can be a benefit - although this is probably irrelevant since no one is likely to be going through significant film just for their footwear photography.

So, based on the above, the last issue becomes the most important. It is probably also the most debated issue. Some people have had bad experiences with digital - my guess is this is due to a lack of good training, or some other explanable issue. I know someone who said one of their crime scene investigators complained that their night photos were lousy after switching to digital. This person suggested looking at the investigators old cases shot on film. Guess what - they were also underexposed. The issue wasn't one of digital technology, the investigator just was finally seeing his own photos and assumed that he had been taking better photos than he had been. Digital brought this into the light and enabled the photography issue to be corrected.

I am rambling now - but I hope some of this was helpful.

George

First, I suggest that you filter through George Reis's ramblings and take to heart what he has to say.

However, if you truly want some technical research info regarding film vs digital, I can offer a couple of resources (although not directly footware, or even forensic related).

Ken Rockwell has suggested that 25 megapixels (MP) would be required to simulate 35mm practical resolution.

R.N. Clark has suggested that about 16 MP could be equal to 35mm.

More recently, Norman Koren has suggested that 8.3 MP may effectively be the equivalent of 35mm (based in part on a signal to noise ration applied to film grain).

I put no particular significance on the above opinions. Ultimately you must do your own reading & research.

The most persuasive recent information I have seen indicates that approximately 12 MP on a full frame sensor, high quality camera is the equivalent of 35mm. Unfortunately, I am unable to immediately locate the reference.

Hope this is more help than complication.

Forgot to mention that a google search of the named references would lead to webpages containing the actual research data.

The Institute for Forensic Imaging in Indianapolis has recently completed research regarding footwear impressions and using digital photography to record them. Their research should be published soon, and they will be presenting their findings at the IAI in Boston. If you would like to contact them for some immediate help, here is their information:

Institute for Forensic Imagaing
Irvington Office Center
338 S. Arlington Ave, Suite 111
Indianapolis, IN 46219

317-356-0245

jjacobia@ifi-indy.org

I hope this information helps others as well.

Kelly,

I suppose the ultimate goal of footwear photography is the individualisation of the mark with a suspect's footwear.

Schallamach wear pattern is arguably the "smallest" individualisable fine detail in footwear.

Testing for our new software learned that 1000 to 1200 ppi grayscale is needed to visualise that kind of detail sufficiently (and yes, I know resolution is not the whole story).

FYI : A full size shoeprint at 1046 ppi 8 bit gray-scale (BVDA gellift scanner) in uncompressed tiff will generate a 80 Mb image file. As a shoeprint examiner, I feel comfortable with this kind of imaging.

None of the SLR digital cameras gives me the same quality and feeling (nor does a standard 35 mm B&W 125 ISO film by the way). Do we always need such quality ? Most of the time not. But you can't tell by just looking at a mark what quality you will need to have "sufficient" detail.

So qualified crime scene personnel in our country sticks to film as it comes to photographing footwear marks on crime scenes. If possible, evidence will be brought to the lab for enhancement and/or photography with 4x5" or 8x10" film or imaging with scanners.

All the best,

Gerrit Volckeryck
Federal Police
Belgium

I can remember before digital the NZ Herald newspaper published on their front page every April Fools Day some impossible photo like an American warship parked in the middle of Auckland's Queens St (the main drag), my point is, almost everything that can be done with digital can be done with normal chemical photography it just takes a lot longer.

George is right, you need to decide what quality is needed, and go from there.

We can only see so much, so is there much point in providing 100% more unless you are enlarging the image to put on a bill board.

I have heard 13mp is = to 35mm film but my source also told me comparing digital to film is like comparing apples and oranges.

So until there is a definitive solution to this possible problem I photograph shoeprints using both formats. However in every case that went to a shoeprint examiner so far they used the digitals for their examination

Of course the day is coming when 35mm film will be talked about in the same breath as 8 tracks and record players, then what?

The key is to find what level of detail your examiners need (whether shooting film or digital). Determine the length of the subject that your digital camera, or your film camera / film combination can capture with that level of detail. If that length is less than the length of your subject, then shoot one image to show the whole subject, then tighter, overlapping shots for the fine detail. This standard approach is valid for 35mm, medium format, large format, point-and-shoot digital, dSLR digital, scanning back digital, etc. Test, measure, evaluate, apply. The tool you use isn't important - using it correctly is.

George

From my understanding 'apples to oranges' is a good analogy. The way film based cameras and CCD or CMOS based cameras respond to light in different manners.

The overall key here is NOT to attempt to equate film to digital. You need to determine what your minimum requirements are (quality wise) to capture all the detail in the impression and then use equipment and techniques that fulfill or exceed those requirements.

George is right about shooting multiple images and overlapping. I imagine that the average shoe impression is <12". Using 12" and breaking that into thirds with a half inch overlap would give you 4.5" wide shots. I set up my camera (D2X, 12.2 mp) so a full frame shot covered 4.5". I scaled the image 1:1 and came up with a resolution of ~941 ppi. This is very close to SWIGIT's recommendation of 1000ppi for fingerprint comparison images.

Is 941 ppi sufficient resolution to capture all the fine detail of the impression? Maybe, it depends on the examiner and the impression. Could I get higher resolution photos by taking tighter shots? Absolutely.

Determine your needs based on the equipment you have and the quality of the impression and go from there....

2006 IAI Educational Conference Program

GLScan, a Dedicated Hi-res Scanner for Gel Lifts
Friday, July 7, 2006 8:00 a.m. - 8:30 a.m.
Room: Marriott - Wellesley

Jan Zonjee, PhD
BVDA International b.v., Haalem, Netherlands

Digital imaging has made major inroads in crime-scene units and forensic departments due to its advantages over traditional photography. However, when a shoeprint needs to be photographed the resolution is unsuitable for making comparisons. Scanning can overcome this, but scanners intended for office use are limited in their capabilities to scan shoeprint lifts. In this lecture the need for a dedicated scanner will be demonstrated.

http://www.bvda.com/EN/sect16/en_16_4a.html