CLPEX Chat Board

I recently found out that a Fingerprint Unit in my own country works with colour images of ninhydrin impressions as opposed to black and white. All of the other Units in my country work from black and white.
I would be obliged if any Fingerprint Examiners out there could let me know if they too choose to use colour ninhydrin images for comparison work and why they feel it is better.
(As far as I know they still work with black and white fingerprint forms and not purple and white !!)

White or fluorescent powders must throw a spanner amongst the works

Black, White, Purple, Green, Blue, Yellow, Chartreuse. It doesn't matter to me, I am looking at the image.

briano wrote:Black, White, Purple, Green, Blue, Yellow, Chartreuse. It doesn't matter to me, I am looking at the image.

Hi Briano,

I agree we are all looking at the image but surely we want to work from the best image available.

I like to use both. For the most part do my comparisons in photoshop so I will have an enhanced B&W and original color image up, and sometimes I will get the evidence if I have it. Even with dye stain/ALS images I like to use those over B&W sometimes. But it is a personal prefernce, to each his own.

redlion62 wrote:

briano wrote:Black, White, Purple, Green, Blue, Yellow, Chartreuse. It doesn't matter to me, I am looking at the image.

Hi Briano,

I agree we are all looking at the image but surely we want to work from the best image available.

Black and white doesn't guarantee the best image available.

If I have a ninhydrin print that, without any enhancement, is sufficient enough for comparison then I will do it from the raw image. If I individualize the print, my documentation will include the raw image with whatever markings I use for that documentation.

However, if I have a print that needs enhancement, it will end up in grayscale based on my usual choice of enhancement methods converting it to grayscale.

If I have a CA fumed item with white ridges, I normally don't bother inverting the colors to make them black either. Latent print ridges don't have to be black and furrows white to conduct a comparison.

Totally agree with Steve.

A ninhydrin print that is scanned/photographed then 'adjusted' using channel mixer or Black and White will always produce a far superior image to a black and white photograph.

Channel mixer also produces spectacular results with thermal paper treated with ninhydrin.

Color photography of ninhydrin prints allow you to use color channel isolation. Convert the image to CMYK and isolate the magenta channel. In the magenta channel you can enhance it further and then convert it to grayscale. Isolating the magenta channel allows you to drop out other colors and focus primarily on the purple ridges. I have used this several times with excellent success.

Robert Miller wrote:Convert the image to CMYK and isolate the magenta channel. In the magenta channel you can enhance it further and then convert it to grayscale. Isolating the magenta channel allows you to drop out other colors and focus primarily on the purple ridges.

Robert,

Have you used the Black & White adjustment? It allows you to remain in RGB yet make adjustments to Red, Green, Blue, Cyan, Magenta, and Yellow at the same time. No need to do any conversions. The output is in grayscale.

I agree with Steve Everist on this one. Shoot in color and then use Photoshop's B&W converter and adjust individual channels for the best results. I have also found that leaving the image in color and inverting the colors works very well for me in some cases. The end product usually ends up being light green ridges on a black background. I have also tried photographing Ninhydrin prints with my digital camera set to B&W and using filtration applied to the lens. However, with my particular camera system I have discovered that the RAW files remain in color and that the JPEG files show as B&W. I think the B&W photography of Ninhydrin prints is a holdover from the days of film. When using a panchromatic B&W film one would apply a green filter to the lens to photograph the Ninhydrin prints making the Ninhydrin prints darker in the resultant photographs. Now with digital and Photoshop all sorts of amazing things can be accomplished with color digital images.

Any photo or scan performed today is RGB from a digital acquisition device unless you're a luddite using the remainder of the world's B&W film stock. Depending on the device, a digital image may well be "enhanced" by the camera's default settings unless you intentionally turn them off. Most scanners do not "enhance" an acquisition unless you use the scanner software to do so prior to that particular scan or have saved and retained a scan input setting for that session. Cameras, even the better SLR models from Canon, Nikon, etc. will come from the factory with a default setting that includes a bit of "sharpening" and color saturation boost to give users a bit better display on the LCD, I suppose, or to result in a better average image for the "point and shoot JPEG" users. What I'm saying here is that, unless you turn off the default settings in your camera menu and zero out the sharpening and saturation (and any other settings), you already are working on a "factory enhanced" image with slightly distorted color. Throw in the wavelength of the light source and filters (if any) used to capture the image, and most any image can be improved with a bit of enhancement in a digital image editor, especially if you have a preference in working in B&W. As an aside, when I took the fingerprint photo training at the FBI Academy in Quantico, much of the class was devoted to using Photoshop techniques to enhance images from their Nikon cameras for print display. Be sure your Photoshop or other image editor is set to record all your steps so they can be replayed in court if so requested.