FIC Week 2 Flashcards
What is the purpose of development powders?
• To make the latent impressions visible
• To create contrast with the background
• To enable the impressions to be photographed
• To enable the impressions to be lifted
What is matrix made up of?
Sebaceous Oils
Lipids
Eccrine Sweat
Other Contaminants (grease, blood, etc.)
Factors to consider for longevity of impressions?
• Atmospheric conditions
• Substrate
• Composition of matrix
• Amount of matrix
• Contamination
Desirable qualities of powders
• Sensitivity to secretions and wet/oily transfer
• Adhesive qualities
• Reproducibility(consistent results)
Types of development powders
• Regular
• Fluorescent
• Magnetic (Regular & Fluorescent)
Fluorescent Powder
• Best Used On:
• Multi-colored surfaces
• Cut crystal
• Glossy magazine covers
• Photographs
• Possible Signature: must be applied with UV light otherwise will have too much powder
Magnetic powders
• Limited volatility
• Primarily for recently handled items (12- 24hrs)
• Can be applied to wood, paper*, leather and other porous surfaces.
• May be used to enhance F/P developed with regular powders
• Difficult to apply on vertical surfaces
• Difficult to apply on ferrous metals
Why the letter “R” when labelling prints?
• Indicates the laterality at the moment the print was recorded.
• You can use “F” for footwear.
• Some services use “P” for palm.
Two types of camera sensors?
• CCD: A solid state image sensor called a Charge Coupled Device (can experience vertical smearing)
• CMOS: Complementary Metal Oxide Semiconductor
Two types of compression schemes
• Lossy
• Lossless
Pixels have 3 properties
• Size
• Location
• Color value
Colour interpolation
is used to represent the colour values in a digital image
Resolution
• Resolution can be identified by the measurement of pixels in dimensions of height and width
• The resolution of an digital image is measured in pixels per inch
• Typically a higher resolution equals a better image
Exposure Triangle
• ISO
• Aperture
• Shutter speed
Increasing Depth of Field
• Smaller aperture (larger number)
• Increase the camera to subject distance
• Use a shorter focal length
Metering Modes
Matrix
Centre Weighted
Spot
Inverse Square Law
• The intensity of light reaching an object is inversely proportional to
the square of the distance between the object and the light source
Focal length
The focal length of the lens is the distance between the lens and the image sensor when the subject is in focus
Lens speed
the maximum aperture diameter, or minimum f-number, of a photographic lens
The best location for the scale on a fingerprint impression is…
Longitudinal to the print
Which researcher is known for studying bias in forensic science?
Itiel Dror
Why is aperture priority the preferred camera mode for forensic photography?
This mode better controls depth of field.
What are the three properties of a pixel?
size
location
color value
What is the calculated error rate in the FBI/Noblis black box study (Ulery, B. T.; Hicklin, R. A.; Buscaglia, J.; Roberts,
M. A. Accuracy and Reliability of Forensic Latent Fingerprint Decisions. PNAS 2011, 108 (19). 7733-7738
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