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Monday, August 13, 2007

The purpose of the Detail is to help keep you informed of the current state of affairs in the latent print community, to provide an avenue to circulate original fingerprint-related articles, and to announce important events as they happen in our field.
Breaking NEWz you can UzE...
compiled by Jon Stimac

'Enough Evidence' for Lotz Trial to Proceed  INDEPENDENT ONLINE, So AFRICA - Aug 8, 2007 ...defense advocate asked for a postponement to allow for two foreign fingerprint experts to travel...

Fingerprining Snares Visa Cheats BBC NEWS, UK - Aug 8, 2007 ...more than 6,000 potential immigration cheats have been identified by a new plan to fingerprint visa applicants...

New Fingerprinting LOGAN DAILY NEWS, OH - Aug 10, 2007 ...Municipal court judge purchases equipment for office and sheriff's department...

British Man Seeks Clemency for Murders MIAMI HERALD, FL - Aug 9, 2007 ...fingerprints on plastic wrap used to tie one of the victims and other evidence that he owned a handgun...

Recent CLPEX Posting Activity
Last Week's Board topics containing new posts
Moderated by Steve Everist

Subpoena the Verifiers
sharon cook 168 Sun Aug 12, 2007 7:46 pm

John's Quote about Confidence and Probabilities
g. 5394 Sun Aug 12, 2007 7:01 pm

Scotland in September
Ernie Hamm 584 Sun Aug 12, 2007 3:04 am

The Lockerbie Connection.
Iain McKie 14492 Sat Aug 11, 2007 9:07 pm

New book for Photoshop users.
Andrew Schriever 263 Wed Aug 08, 2007 5:53 pm

Statistics and Misidentifications - The weeks Detail
Michele Triplett 15581 Tue Aug 07, 2007 11:25 pm

Fingerprint Society Seminar - November
fpsociety 277 Tue Aug 07, 2007 8:48 pm

Footprint (Friction Ridge) Comparison
Charles Parker 269 Mon Aug 06, 2007 11:03 am



No major updates on the site this week.


Last week

we looked at the new re-certification guidelines for many of the IAI disciplines.

This week

Andrew Schriever and Casey Caudle bring us a look at efficient workflow techniques for detailed color space examination.  Their workshop was one of the more helpful ones I attended at the IAI conference in San Diego and I was happy that they accepted the invitation to pass on a few very helpful Photoshop tips. 

Channel Splitting for Identification Specialists
by Andrew Schriever, CLPE; and Casey Caudle, CFVA
Target Assets Protection Forensic Laboratory


Examiners are faced with many difficult challenges when processing digital images.  Digital images contain both useful and distracting information.  The distracting information may be caused by color interference, repetitive patterns and blur.  Many of these challenges can be identified through a careful analysis of each image.  For image processing to achieve optimal results, the analysis phase is imperative.   

This article will focus on establishing a method to analyze color images prior to applying specific filters or processes.  In particular, this article describes channel splitting.  Channel splitting is useful to examine the contents of individual color channels within an image and allows you to analyze an image so that its colors can be later isolated. 

Often, it is effective to see each color channel of an image displayed side-by-side.  This allows you to determine which channel(s) are contributing the most information to the detail you are interested in.  You can focus on what is important while quickly identifying the distracting information – such as the ridges of a fingerprint in one color channel & the distracting noise or pattern in another color channel. 

Analyzing an image by splitting color channels allows examiners to make informed choices about the most effective color space and color isolation technique for a particular image.  Color isolation allows one to maximize the clarity of identifying characteristics and reduces other distracting color information.  There are many other ways to isolate specific colors in Adobe Photoshop including channel mixer, calculations, hue & saturation and even working solely on one color channel.  


The most common color spaces native to Photoshop are RGB (red, green, blue), CMYK (cyan, magenta, yellow, black), L*a*b (lightness, a, b).   

First open an image in Photoshop then create a duplicate of that image (Image -> Duplicate), and perform your channel splitting process on the duplicate.  Open the Channels palette by clicking on the tab labeled “Channels”.  If you can’t find the Channels tab on your Photoshop screen, click on the “Window” menu at the top of Photoshop and make sure that there is a checkmark to the left of “Channels”. 

Depending on the color space of the image you opened, you will see the different color channels present in the Channels Palette (CMYK for this image).  You can view the information that the individual color channels are contributing to the image by simply clicking on the individual channels (note – click on the small thumbnail image or the name of the channel).


To view the individual color channels for another color space convert the image to the desired color space (Image ->Mode->RGB/CMYK/Lab).  The individual color channels for whichever color space you selected will be visible in the Channels Palette.  Each color channel will display a small thumbnail image of the color channel and the name of that particular channel.

You can view each color channel as a separate image by using the “Split Channels” function.  Open the fly-out menu on the Channels Palette by clicking on the circle button with the arrow in it (located directly below the red x).

The third option from the bottom is “Split Channels”.


When you click on the “Split Channels” function, Photoshop will open new images.  Each image displays the information from one color channel.  The name of each image will be appended with a letter denoting which color channel that image is displaying.


The above graphic shows an image that was in the CMYK color space and the split channels function performed.  You can see that Photoshop split the original image into 4 new images, each image displaying one color channel.  Circled in red is the portion of the image name that denotes which color channel each particular image is displaying (K for black, Y for yellow, M for Magenta, C for Cyan).

To view the images side-by-side, click on Window -> Arrange -> Tile Horizontally.    This will arrange all open images on the screen.


Tiled Images

To ensure that all images are displayed at the same magnification and position, go to Window -> Arrange -> Match Zoom and Location.  The Hand Tool and the Zoom Tool can be configured to allow you to zoom and scroll all images at the same time.  Select the “Hand Tool” (keyboard shortcut H) from the Tool Bar and check the box next to “Scroll All Windows” near the top of the screen.  Next select the “Zoom Tool” (keyboard shortcut Z) from the Tool Bar, and check the box next to “Zoom All Windows”.

Note:  Activate the Zoom tool (Z) and click anywhere within one of the images to zoom in on all images.  Hold the Alt key and click inside an image to zoom out of all images.  Press and hold the space bar and drag within any one of the images to scroll all images to the same position.

This process can be performed in all available color spaces at once.  To view all 10 channels (R, G, B, C, M, Y, K, L, A, B) at the same time; open an image, make 3 duplicates, convert each one to a different color space, and perform the split channels function on each duplicate.  This will allow you to see every available color channel as an individual image and you can view them side-by-side by tiling the images and locking the zoom and scroll functions as described above.  This can take up a lot of screen real estate, so it is a good idea to press the “Tab” key before tiling the images on the screen.  Pressing the “Tab” key will hide all palettes and the tool bar from view, allowing the images to fill the entire screen.

Automation of the process

Photoshop allows users to automate many processes through the use of actions and scripts.  Users can create a custom action or script to automate the channel splitting process, based upon their individual needs.  We have supplied with a set of custom actions that automates the channel splitting process. 

One action in the Split Channels set is Color Channels.  This automates the processes described above creating a separate image for each color channel.  The user can run this action on an image, and then tile the images for viewing.

The second action, Channel Preview, will allow you to view all the color channels from all the color spaces available (including desaturation and grayscale conversion) in the channels palette of one image.  (as illustrated at right)

Loading Actions

Download the action by right-clicking on the link below and choosing "Save target as"

Split Channels Action

Save it to the following location on the computer with Adobe Photoshop:

C:\Program Files\Adobe\Adobe Photoshop CS2\Presets\Photoshop Actions

If a different version of Photoshop is being used, replace the CS2 portion of the path with the version number that is currently installed.

Do the same procedure on this Sample Image link for an image to download and practice channel splitting.

Select the fly-out menu in the actions palette and select load actions.  Navigate to the new action set named “Split Channels”.


G. Reis, (2007). Photoshop CS3 for Forensics Professionals, Sybex Publishing, San Francisco, CA.

J. C Russ, (2002). The Image Processing Hand Book, Fourth Edition, CRC Press, Boca Raton, FL.


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Until next Monday morning, don't work too hard or too little.

Have a GREAT week!