Black and White Contrast Filters


Steven Staggs
© 2014 from the book Crime Scene and Evidence Photography, 2nd Edition

Film

Well–defined fingerprints can usually be photographed with color film. However, black–and–white film provides greater contrast than color film and is preferred for latent print photography. The following is a list of a few black–and–white films that are suitable for latent fingerprint photography.

Normal contrast photographs can be taken using a professional black–and–white film such as Kodak T–MAX or Ilford Delta Professional films. For best results develop Kodak T–MAX film in T–MAX developer and process Ilford Delta Professional films in ILFOTEC HC developer. A little higher contrast can be obtained by increasing the film development time by twenty-five percent.

Some black–and–white films can be processed in color processing machines. You can take these films to color photo labs for processing in their color equipment. Kodak Professional BW400CN and Ilford XP–2 Super are black–and–white films that are processed in color processors. They each have an ISO of 400, are fine grain with good sharpness and resolution, and are processed in C–41 color chemistry.

In black–and–white photographs all colors become shades of gray. This can be a problem when two colors become nearly the same shade of gray in a photograph. However, colored filters can be used to increase contrast between colors in black–and–white photographs. Color filters can build contrast by either lightening or darkening the latent print, or by lightening or darkening the background. To lighten a color, the color filter closest to the color is used. To darken a color, the opposite color filter is used. (See the following two tables for information on using filters with black-and-white film.)

Black and White Contrast Filters

Objective: To increase contrast between two colors that would normally photograph as nearly the same shade of gray using black and white film.

Light Information — White light is made up of a mixture of red, green and blue (primaries). In theory, red, green, and blue light sources simultaneously projected on the same area will be white. Red and green light mixed together makes yellow. Green and blue light mixed is cyan. Blue and red light mixed is magenta.

Light Transmission Law — The filter transmits its own color (lightened in the print) and absorbs (subtracts) is complementary color (darkened in the print).

Filter ColorFilter DesignationAbsorbs (Darkens)Transmits (Lightens)
Red25A, 29Blue & Green — CyanRed
Blue47,47BRed & Green — YellowBlue
Green58, 61Red & Blue — MagentaGreen
MagentaCC50MGreenRed & Blue — Magenta
CyanCC50CRedGreen & Blue — Cyan
Yellow8, 15BlueRed & Green — Yellow


Selecting Black and White Films and Filters toObtain Contrast Between Colors

Desired Photographic ResultFilters used to obtain result
Blue as BlackRed (25, 29)
Blue as WhiteBlue (47, 47B)
Blue-green as WhiteCyan (50C)
Blue-green as BlackRed (25, 29)
Green as WhiteGreen (58, 61)
Green as BlackRed (25, 29) or Blue (47, 47B)
Orange as BlackBlue (47, 47B)
Orange as WhiteYellow (15) or Red (25, 29)
Red as WhiteRed (25, 29)
Red as BlackBlue (47, 47B)
Violet as WhiteBlue (47, 47B)
Violet as BlackGreen (58, 61)
Yellow as BlackBlue (47, 47B)
Yellow as WhiteYellow (15)
Yellow-green as WhiteGreen (11, 13)
Yellow-green as BlackBlue (47, 47B)

NOTE: As colors of objects are hardly ever "pure," the effects described are never perfect but the direction indicated is correct.


Black-and-white film and without any filter — the background and fingerprint record as nearly the same shade of gray.
     
Black-and-white film and with a red filter — the red filter transmits the red background providing needed contrast.

For example, a black powdered latent on a blue background would be difficult to see in a black–and–white photograph. However, the latent print can be enhanced by causing the background to lighten by using a blue filter. A ninhydrin developed latent on the back of U.S. currency can be enhanced in two ways by using a green filter. The green ink in the currency is lightened (the background is lightened) and the violet colored ninhydrin developed latent fingerprint is darkened.



Creative Commons License Black and White Contrast Filters  Copyright: © 2014 by Steven Staggs. Copyright for this article is retained by the author, with publication rights granted to the Crime Scene Investigation Network. This is an Open Access article distributed under the terms of the Creative Commons Attribution-NonCommercial-NoDerivatives 4.0 International License which permits unrestricted noncommercial use, distribution, and reproduction, provided the original work is properly cited and not changed in any way. Based on a work at http://www.staggspublishing.com/CrimeScenePhotography.html.



About the Book

The information presented in this article is from the book
Crime Scene and Evidence Photography, 2nd Edition © 2014 by Steven Staggs.

Crime Scene and Evidence Photography, 2nd Edition is designed for those responsible for photography at the crime scene and in the laboratory. It may be used by law enforcement officers, investigators, crime scene technicians, and forensic scientists. It contains instructions for photographing a variety of crime scenes and various types of evidence. It is a valuable reference tool when combined with training and experience. Crime Scene and Evidence Photography is also a helpful resource for students and others interested in entering into the field of crime scene investigation.

Crime Scene and Evidence Photography, 2nd Ed may be purchased from the publisher at a 20% discount.



About the Author

For the past 30 years Steven Staggs has been a forensic photography instructor and has trained more than 4,000 crime scene technicians and investigators for police and sheriff departments, district attorney offices, and federal agencies. He is also a guest speaker for investigator associations, appears as a crime scene investigation expert on Discovery Channel's Unsolved History, and provides consulting to law enforcement agencies.

Steve has extensive experience in crime scene photography and identification. He has testified in superior court concerning his crime scene, evidence, and autopsy photography and has handled high profile cases including a nationally publicized serial homicide case.

Steve is the author of the Crime Scene and Evidence Photographer's Guide, a field handbook for crime scene and evidence photography, which has sold over 40,000 copies and is in use by investigators in more than 2,500 law enforcement agencies.

Steve retired in 2004 after 32 years in law enforcement, but continues to teach forensic photography and crime scene investigations at a university in Southern California. He is the President of Crime Scene Resources, Inc. and Webmaster of the Crime Scene Investigator Network, the world's most popular Crime Scene Investigation and Forensic Science website (www.crime-scene-investigator.net).



Article submitted by the Author
Article posted: September 30, 2104