ScienceGL: Forensic Image Analysis, Comparison and 3D
1. General notes. Introduction.
Generally 3D image enhancement is an easy procedure, but it requires some understanding of what 3D surface is all about. As a reward of spending time on basic concepts below, you will gain a very powerful tool.
The idea of 3D enhancement and visualization is very simple. We just apply to your personal experience in the real world. Experience on how the real things (or objects) look like. As we live in 3D rather than 2D photography world, we used to see some details of the objects that are lost in 2D pictures. For example when you want to see some scratch on CD surface you will automatically try to look from different directions until you find the correct angle of view. This procedure seems to be natural and simple, but in fact what happens is that you are using your powerful brain “computer” to find optimum lightning and viewing perspective at which you see the scratch. Or, more technically, you are looking for illumination condition such that cave of scratch results in nicely contrasting reflection into direction of your eye.
Now think of scratch as a tiny feature of the surface. And think of 3D software as a tool that allows you to imitate real live, i.e. imitate the way you would go looking for the scratch if you had it on real object. You are close to understand why 3D software is useful for image enhancement. Simply because it is used in conjunction with your brain to see on images what is hard to see otherwise.
Until very recently the 3D was exclusively used by professionals (movie makers, web designers, etc.). We tried to make it easy for scientist or expert from not related field, who can not afford spending much time playing around with PC, but rather needs a tool to see what's on in his practical problem. So, we made the software that will make you immediately productive. This example is aimed to streamline your 3D experience and productivity.
The sowtware was specificaly developed for forensic questioned document examiners.
It supports hyperspectrum data processing and visualization.
Just run setup MSI file to perform software installation.
3. Loading Files
Run the program. Use Menu>File>Read to load the file into the program. Press Histogram to see distribution of Z levels (heights ) in the image.
In the case of the sample image enclosed to install you will see the image like Fig.1.
Fig.1. Forencic questioned document measured with hyper-spectral equipment
such as ForensicXP.
Screen after image file load and Histogram tool activation. On histogram plot (right) you can see 4 picks that correspond to Background (1), pen1 (2), pen2 (4), and intersection of the pens (3).
NOTE: the image intensity level is interpreted as Z height of
the 3D plot. Black interpreted as Z=0, white as Z=max. We have enclosed
to the package an inverted image that looks like Fig.1. If your loaded
image looks opposite. Please invert it with Menu>Data>Flip Z.
Fig.2 Forensic digital image that resulted from 4D hyper-spectrum processor output. You can invert this using Menu>Data>Flip Z.
4. Pre-processing Images
Let us call each pixel gray scale level as Signal. Normally useful signal is smaller in Z range than the whole scale. Choosing the correct scale is more or less similar with contrast and brightness settings in 2D processing. or can use histogram tool to decide the correct Z scale of the interest.
Fig.3. Histogram plot of forensic digital image. The plot is used to optimize Z scale (contrast / brightness).
For example in image presented as Fig.3 the optimum range is somewhere
lying somewhere between two magenta markers (i.e. between Z= 300 and 650).
In order to optimize Z scale you can use Z filer called from Menu>Data>Filer
3D. You will see the corresponding form.
The optimal settings for Minimum and maximum Z level is described in help at "Set Z range: Z filter" topic. Basically from histogram you can decide the optimal Z range setting. You can use our advanced automatic Z range finder. To do so you just press "Auto: button in Z range form.
Fig.4. Automatic Z range selector for 3d enchancement of forensic image.
You can press "OK" to accept suggested Z range. If you do so with your
data, you will see the result as in shown in Fig.5.
NOTE: before you make the decision of the Z range selection you might consider of using smooth filter that will remove noise from the image.
Please see Menu>Date>Smooth 3D.
Pre-processing of images requires some experience. The good news with
our software is that our ca do all this in automatic mode.
Please use Menu>Data>All Auto
For the sample you find in our package you will get the result shown in following picture.
Fig.5. Automatic data Pre-processing of digital hyperspectrum data set of a questioned document.
Automatic pre-processing includes following operations:
1. Smooth of the data.
2. Automatic Z range selector.
3. Cut Z offset.
This set of the pre-processing functions will produce optimal results
in most of the cases of the digital images.
We recommend to use this feature unless special case of pre-processing is required.
5. Visualization 3D: Pan, Zoom, Rotation.
You can pan the surface either with mouse or with scrolls. For scroll
operation use Menu>View>Scrills
For mouse operation press Shift - MouseDown inside 3D window. The "hand" pan mouse marker will appear.
Moving mouse without releasing will result in Pan operation.
Fig. 6. a, b. Pan with mouse. Drag mouse within 3D window with Shift key pressed.
You can Zoom the surface either with mouse or with buttons. For button
operation just click the button "Lens +" or "Lens --".
For mouse operation press Alt - Mouse Down inside 3D window. The "magnifier" zoom mouse marker will appear.
Moving mouse without releasing will result in Zoom operation. effective Zoom also can be achieved by moving camera closer to the surface.
See ADVANCED ZOOM issues.
Fig.7. a, b. Zoom with mouse. Drag mouse within 3D window with Alt key pressed.
Rotations in 2 axis is achieved by dragging mouse within 3D window.
ADVANCED ZOOM: Zooming surface with "Magnifier" buttons and with
mouse effectively works as if you where changing your camera ZOOM lens
(i.e. angle of observation). This operation changes perspective of the
scene. At small observation angles (i.e. large zoom) you loose quality
of the 3D rendering.
You can achieve zoom effect by moving the camera toward to or away from the surface. This produce different visual effect because you keep same perspective and also because you get better quality of the rendering at large zoom. We recommend to use "Magnifier" buttons for medium zoom power and for zooming out. In the case when you need maximum detail of the surface we suggest you to use "Camera closer" kind of zoom.
Fig.8. Camera distance buttons. Left is "Camera away" (zoom out), Right is ""Camera closer" (zoom in).
6. Volume tool, Metrics
The most important part of making measurements is to introduce the correct
sizes of the image under inspection.
You can use the special form called from Menu>Data>Calibrate XYZ.
Fig.9. Calibration of the measuring tools.
The image Z size is in fact artificial so you can put anything, but
to estimate the Volume of the observed features on 3D we recommend
you to use the size of about 10% of the XY size
Let us suppose that image was 1x1.5 millimeters in size, then we suggest to place 0.1 mm as height size.
The X,Y, and Z scale MUST BE SET TO SAME UNITS like mm or microns.
NOTE: If you do not introduce the X,Y,Z sizes the read out of the tools
X - Pixel units
Y - Pixel units
Z - Z level of the image loaded
After you introduce the X,Y,Z sizes you can read out directly mouse
position in terms of X,Y,Z co-ordinates.
Please activate mouse read out with corresponding button.
Fig.10. Activation of mouse read out.
Press "xyz read" button, it will change the caption to "xyz ON" as it
is shown in Fig.10.
If you press same button second time you will disable mouse read out and see "xyz OFF" caption.
We suggest that you use mouse read out activated ONLY WHEN YOU REALLY NEED READINGS.
Because this mode is considerably slower in terms of rendering (animation).
Now you can drop measurement tools into 3D scene.
Press "Volume" button (same as Menu>Tools>Volume)
See semitransparent cube. Adjust the planes of the cube to the feature of interest.
Fig.11. Volume tool, activated with "volume" button. Mouse adjustable height and sides of the cube. While adjusting to box height (top Z plane), you can use histogram plot and status bar (marked with magenta arrows) to see Z plane position.
Fir.12. Forensic 3D measurement tools. Volume measuring cube. Returns position of all corners. If active, also returns the volume and area of the features.
Upper plane of the cube is moved by dragging the cyan corners. Please refer to our Help on mouse driven operation with Volume tool and also Volume/Area section of the help for explanation of the measured parameters.
One of the most important tasks in comparison of different pens is accurate
evaluation of the heights one feature relative to another. You can use
(orthogonal plane parallel to Z axis) to do this. This tool is also known as Water-line.
Fig.13. Forensic questioned document analysis tools. Water-line tool. Semitransparent plane movable with mouse. While moving plane you can read out its Z position in Status bar. Red arrow in the figure.
You can mark features of the interest with 3D labels.
Fig.14. Forensic document report for digital image under inspection. Labels and pin markers. Called from Menu>Tools>
You can move pin and update related marker with "Link to Pins" menu
click, see Fig. 15.
You can save Labels with corresponding Menu in Labels sub-form.
7. Using Light, surface reflection and contour enhancement.
Possibility to change the light angles and conditions is a great enhancement
feature. As it shows you the 3D features in natural realistic way.
In the Menu>Options> you will find Reflection and Diffused options.
Fig.15. Normal Shadow:
Reflection is OFF, Diffused is OFF.
Fig.16. High reflection. Reflection is ON. Diffuse is OFF.
Fig.17. Diffused. Reflection is OFF. Diffuse is ON.
You can adjust light position using mouse Drag operation within light
Fig.18. Inclined light for shadowing and realistic effects.
Now you can enable contour plot for "map like" effect. Use Menu>Options>Contour
Fig.19. Contour option is ON.
You can change number of visible contour lines by right/left clicking
at the Z Palette sub picture at the right top side of the main form.
Please see help for details.
The software is available as turn key application or as user programmable
API for C++, C#, VB.NET, VB.
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