Introduction to Color Filters in Forensic Photography

Introduction to Color Filters in Forensic Photography

Introduction to Color Filters in Forensic Photography

A filter is a transparent material that absorbs some colors and allows others to pass through. A color filter is the sheet of transparent material which modifies a light beam by absorption of some colors with respect to others. A neutral filter absorbs all wavelengths equally and merely serves to reduce the intensity of a beam of light without changing its color.  The color filters are mainly used to enhance the quality of the particular object when captured. It only allows the particular frequency of light to pass on and radiate only such amount of light.

  • Filters can be divided into three main categories:
  • correction filters: for the correction of the wavelength of the light entering a lens
  • protection filters: to protect the front lens
  • effect filters: to give a special effect to an image.

The latent fingerprint was not visible clearly without the filter; hence we applied the filter and use modern technology to make the prints more focused which easily be detected by the investigator. Lately, we can see that the prints are more accurately be seen with the black and white filter because it doesn’t give a peculiar idea or exact pattern of fingerprints. So, it is uneasy and a bit difficult to recognize the prints and study its pattern in the colorful photograph as evidence.

Technical Photography

The style of photography used at the crime scenes to capture evidence is called technical photography. Crime scene photographers must take high-quality technical photographs to ensure the photographs can be used in the investigation and ultimately in court. Technical photographs are photographs that show as much detail or information about the view or object pictured as possible. The best technical photographs have four characteristics. They are exposed incorrect way, have a maximum depth of field, and are in sharp focus. While frequently there are conditions that make this difficult or impossible (the shallow depth of field can be seen always in close range photographs), crime scene and evidence photographers must strive to take photographs with these characteristics.

Correct Exposure

Technical photographs must be correctly exposed. Correct exposures are necessary for the film to capture all the details in all parts of the scene, including highlights and shadow. Underexposed photographs lose detail in the shadows while overexposed photographs lose detail in the highlight areas. The correct exposure allows the professional to look after accurately and to capture the evidence with likely more perfection. Mainly exposure is controlled by the lens aperture and the shutter speed.  Likely most cameras are operated manually or else can be set in automatic modes. Automatic systems and automatic flash units produce adequate results in most normal situations. However, it is seen that automatic exposure may produce incorrect exposures.

Some common problem lighting situations to be aware of include highly reflective scenes, bright sun lighted scenes with deep shadows and back-lighting.

Bracketing: Bracketing involves making a series of exposures of the same subject at different exposures, usually at one stop or one-half stop intervals. Some cameras can be set to automatically bracket at selected exposure differences from the metered exposure.

High Dynamic Range Photography: With bracketing, you may have two or more photographs to look at to see all the detail in the highlights and shadows in the view. A way to reduce the two or more photographs to one photograph is to use (HDR) photography. High-dynamic-range photographs are generally achieved by capturing multiple bracketed photographs and then merging them into a single HDR image.

Flash Fill: One more valuable technique for ensuring accurate exposures, especially for scenes with deep shadows, is flash fill. In scenes illuminated by bright sunlight, there will usually be dark shadow areas. Sometimes evidence is located in the shadows. The detail in the deep shadow areas may be lost when the exposure is based on the overall brightness of the scene.

Maximum depth of field: Technical photographs must have a maximum depth of field. Depth of field, often called the plane of sharpness, is the area in a photograph where objects are in sharp focus. Crime scene and evidence photographs should have the maximum amount focused as possible (a deep plane of sharpness). This is because out of focus areas of a photograph can become issues in court. An opposing attorney could suggest that you purposely caused an area to be out of focus a photograph to obscure some additional evidence that would are clearly visible if properly photographed.

Sharp Focus: Technical photographs must be in sharp focus. To make sure that your photographs are in sharp focus, keep the camera steady during the exposure. The one should mount the camera on a tripod if the shutter speed is less than 1/60 second and focus carefully. Also, maximizing the depth of the field will result in sharpness in a larger area of the photograph.

Flash Illumination

Types of flash illumination:

Manual Flash: When you use a manual flash set the lens f-stop for the flash-to- subject distance (the f-stop for each distance is usually displayed in a chart on the back of the electronic flash).

Automatic Flash: Automatic flash units use distance ranges. Each range has a minimum and maximum distance. A f-stop is assigned to each range. Changing to a new range requires a change in f-stop. When in an automatic flash, make sure the camera shutter speed dial is set to the flash synchronization speed? When photographing a high key scene (light or reflective background) bracket exposures by opening up one or two f-stops.

Dedicated Flash: The basic dedicated flash unit sets the correct flash synchronization speed when the flash is in operation. It uses an automatic sensor and distance ranges. You must set the appropriate f-stop for the distance range. More advanced dedicated flash units may set both the correct flash synchronization speed and f-stop for the automatic range selected. Dedicated TTL flash — The dedicated TTL (through-the-lens) flash uses a sensor inside the camera to control the duration of the flash. Use smaller lens apertures for short distances and larger lens apertures for long distances. A confidence light or a warning light will indicate whether useable f-stop was selected. If the equipment indicates there was not enough light, select a larger lens aperture and re-photograph. Dedicated TTL flash units can usually be used in manual and automatic modes, as well as TTL.

Bounce Flash: The bounce lighting use for less contrast, softer lighting, reducing the intensity of the light, or to increase the angle of flash coverage. Bounce lighting is accomplished by angling the flash to reflect the flash of a white- or light-colored surface, usually a ceiling. With manual flash, add the space up and down for the flash-to-subject distance and then add in the absorbance loss (one to three f-stops). For bounce lighting utilizing an automatic flash with the flash sensor facing the subject, use a range for two or more times the actual flash-to-subject distance.

Multiple Flashes: To illuminate large areas you can get good results by using several flash units positioned around the scene. The flash units can be triggered simultaneously by connecting them with sync cords or using photocell devices that remotely trigger the flash units when the camera-mounted flash fires. To balance the intensity of each of the flash units, the distance the flash units from the subject to provide the same f-stop value for each flash.

Available Light Photography

Available light photography is particularly useful for big crime scenes at night when a single flash will not provide adequate coverage. Lighting for the photograph may be from street lamps, parking lot lamps, or even moonlight. Available light from street lamps is frequently used at night traffic collision scenes to provide lighting for large areas. You may be able to get an adequate exposure meter reading to operate your camera in manual settings. Automatic cameras may also operate in low-light conditions. Many supplementary exposure meters provide accurate readings in very low-light conditions.

References

  1. West’s Encyclopaedia of American Law (2nd edition, The Gale Gp, 2008).
  2. Bynon, Theodora, Historical linguistics,62(1977).
  3. Webster’s 1913
  4. “Canicid”, http:/en.wiktionary.org.
  5. Chicago Daily Tribune. June 11,1912, page 1
  6. Villiscaiowa.com
  7. http://www.mumbaimirror.com/
  8. http://articles.times of india.indiatimes.com
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