CLPEX Chat Board

So, the age old question...which is better; to clarify or to enhance? We are re-writing our SOPs and have noticed that SWGFAST and SWGIT both use enhance(ment) but I've been getting the feeling lately, at least within the last few years, that clarify is a better term? Anyone care to shed their perspective, especially those from an accredited lab (but I'll take all suggestions!)?

I assume you are referring to digital images right? I think 'enhancement' is a better term...or 'digital image processing' is another term you can use.

Irregardless of the term you are probably going to get accused of 'altering' the image on the stand. Sometimes I think maybe it is best to just use the term 'alter' to begin with and define that in your SOP's

I would agree that enhance is the right word. Clarify implies repitition to make understandable. Enhance implies improving the quality.

In any case, we need to be able to explain in a simple manner some of the basic enhancements. We should know how tools like Levels affects the data in an image and be able to explain why we used that tool.

Enhancement is the right word. If we can explain how and why, we shouldn't need to play semantics.

I think either term is fine. I used to use enhance mostly, now I probably use clarify more. In my workshops, I find that most people seem to be happy with both terms. I'd suggest just making sure that you provide a basic definition of whatever term you decide to use.

George

Thanks for the comments. I think we are going to use 'enhance' but have a definition in our SOP of what it is and EXPLICITLY state that it does not add or remove information in the image.

The other thing that I am dealing with now is the minimum resolution standard. I think George may have touched on this in a previous thread but the optical reolution is different from the nominal resolution for scanners, etc. Why would I want to scan in an image at 1000ppi when the optical resolution of the scanner is either 800 or 1200 ppi? Aren't we extrapolating 1000ppi when we type that in as the captured resolution?

I like to teach people to fill the frame with their latent image; on an 18MP camera, your optical resolution is vastly larger than 1000ppi (something like ~2800ppi or so). Why go through the motions set forth in SWGIT (creating a card that when framed correctly, will give you 1000ppi images) when you can capture at a much higher resolution? Is it because you are down-converting resolutions when entered in to an AFIS database for searching?

I'm just wondering why we should only be capturing at 1000ppi...or, is it just a minimum requirement?

Depending on what enhancement your using, you may be removing information from the picture.
For example, when using the Levels tool to improve the contrast of the picture and make the print easier to see, you are essentially eliminating all of the differences of the brightest and darkest pixels. The grey pixels of the latent are then spread out to make it easier to distinguish the ridges from the furrows. A low contrast print is difficult to see because the shades of grey are too close to each other. Spreading out the greys makes it easier to see, but eliminates some of the differences at the black and white ends of the spectrum. Even though some information is lost while improving the print, all of the information is still retained in the original image.
Most enhancements are a tradeoff between making the part of the picture that we care about easier to see while at the same time eliminating some part of the picture that we don't care about seeing. The information is not permanently eliminated because it is maintained in the original.

Also, if you have a scanner with a native resolution of 800 or 1200, use 1200. All the guidelines say is to use something above 1000. 1000 is just a minimum requirement, not a magic number. (3 is a magic number)

For photographs, fill the frame, but make sure that the inch in the scale has at least 1000 pixels across it. Filling the frame almost always gets you above 1000. Occasionally a palm will be too big to get above the minimum threshold, so just take one picture of the whole palm (at <1000ppi) then more pics of each part of the palm (at >1000ppi). If your camera shoots pictures that are 4200 pixels wide, make sure that your picture is of something less than 4.2 inches wide, and you'll know that the picture is greater than 1000ppi.

I've probably said more than anyone wants to hear regarding the 1000 ppi issue. But, since you brought it up ...

If you want to follow SWGFAST Standards, then scan at a native resolution that is 1000 ppi or higher. For photographs, a simple method for making sure you photograph at 1000 ppi or higher is to know how wide an area will give you 1000 ppi, and always shoot that close or closer. For instance, if the horizontal pixel count in your digital camera is 3872 pixels, then you can photograph something up to 3.87 (3 - 7/8) inches wide. You can mark your ruler to that width, and just always make sure that you are shooting that close, or closer.

George

Re enhancement, if you are using photoshop or paintshop pro you are most likely altering the image, if you are using forensic software you are not altering you are enhancing, ie you are not removing information in the image, V++ is an example and I think the other one is called Imagepro. Any forensic package you buy that has photoshop as its base will alter the image do'nt be fooled into thinking otherwise that is why they save the history with the image.

As for scanning rates there is plenty written on this site about that. If you are filling your view finder with the image with an 18MP camera it is way over 1000ppi. George is on the money once again. I suppose by changing the lens on the camera it all changes.

PPI refers to flat bed scanners (or the very rare beast a scanning camera) DPI refers to Printers, they not the same because a dot is a different size to a pixel.

I'm afraid that I have to disagree with Neville on this one - actually, I'm probably not disagreeing with him, but just clarifying what I think he meant (or is that enhancing or altering it?).

If you are using adjustment layers and smart filters in Photoshop - the original image is preserved in the base layer, and those edits are non-destructive to that original, and are re-editable (similar to the way they work with ImagePro and Amped Five, etc.). One could then suggest that they are not altering the image. But, I would say that the result is altered in all of them, which is the point, isn't it? If the result looks different than it started, it is altered. Sure, it may be altered in a non-destructive manner, but it is altered nonetheless. That's good - that's what we wanted - we altered the image so that it is clearer, has better detail, etc. My point is that "scientific" image processing applications (like ImagePro) provide a result that is different than the original, hence it is altered. And, if you are using adjustment layers and smart filters in Photoshop - you are preserving the image in the same manner as those "scientific" image processing applications.

Regarding the definition of our terms - I think the key is to only adjust the quality of the image but not change the content of it. I teach this as being one point of best practice in the digital imaging workflow, and the definition of "valid forensic procedures" in this workflow.

George

Hi George
I bow to your superior knowledge in such matters, I like to compare enhancement to the good old days of film when you change permanently the negative by how you chemically enhanced developement in the tanks with length of time the neg was left in the different batches of developer, remember how we use to have to allow longer in older developer and the resulting contrast differences, then the shading of the negative when printing and deciding which paper to use, and should I use a long faint light or a short fast exposure or a number of short bright exposures, of course that was after deciding which negative film to use in the first place, I guess nothing is at it appears. It's just that everything is done a lot faster now.