Calculations and other tools

[Lt. Tiv]

there is an excellent article in the July/August edition of the Journal of forensic Identification (Vol. 57 #4) entitled "Image enhancement and Adobe Photoshop: Using Calculations to Extract Image Detail". I've fooled around with calculations but I'm not really sure of what I'm doing. Any thoughts?

[GeorgeReis]

I haven't read the JFI article yet, so I'll not comment on it specifically. But, calculations is a powerful tool. The primary application in using calculations in forensics has been for what I refer to as 'color isolation techniques.' These are techniques used to isolate some data in the image by manipulating color channels. Unfortunately, calculations are not intuitive, but the Channel Mixer is, and you can do many of the same things using the channel mixer - with the added benefit that 1) it's non-destructive/editable if using adjustment layers; and 2) can be easily explained in court if needed.

To use the Channel Mixer, invoke it as an adjustment layer, click the Monochrome box, then adjust the sliders to either mute or enhance detail based on color information. In RGB, sliding any slider to the left makes it darker, to the right makes it lighter. The opposite is true for CMYK values, of course.

In my workshops I provide exercises for this technique to show detail in areas that previously could not be seen (bleached checks), in eliminating security backgrounds behind fingerprints, for isolating signatures from overwritten endorsement stamps, etc.

I hope this is helpful.

George

[robert23]

hi Lt. TIV

bit of a while since you made this posting --but are you still "fooling äround"
with calculations?

Robert

[Lt. Tiv]

I have been using the "channel mixer" (with monochrome checked) along with the various layer blending modes with more success than the calculations. I was having trouble instructing other users on how to use calculations and the other method has been very successful. Most of the time the goal of the project is to increase contrast or remove background interference. The channel mixer is also easier to use than some of the FFT filters I have experimented with. The vast majority of my editing projects involve latent prints.

[Lt. Tiv]

I also forgot to mention that George Reis's book on the forensic uses of PS is an awsome resource. I attended several of his lecturces at the 2008 IAI conference this past summer. He provides some excellent tips on using the various filters.

[DiamondsDr47]

http://movielibrary.lynda.com/html/modPage.asp?ID=506 chapter 13-14
Best regards,

[Lt. Tiv]

Awsome links, these will take some time going through, but it looks like time that will be well spent.

thanks

[robert23]

be good to hear your comment.

[Chain]

In newer versions of Photoshop you can also try the Black & White adjustment layer for this - as it gives you sliders for more colors.

[robert23]

thanks -- i will look further

[cricket1961]

Calculations is very powerful, and yes unfortunately non-intuitive. But don't write it off quite yet. CHannel Mixer is a good watered down version of Calculations and using it can give you some understanding of what to do with Calculations. As will Apply Image.
Calculations is an extraordinary masking tool, color correction tool, channel rebuilder, gradation fixer, detail enhancer, etc.

And Georges book is a good one. Highly recommended.

Chris

[robert23]

thankyou Chris --will look for ur books too