FSC303: Photography

Using a digital camera

1. Point camera to the image to photograph and take the picture.

2. The image is focused on a CCD

3. CCD generates an analog signal that represents the image

4. Analog signal is converted to a digital signal via ACD

5. A processor adjusts the quality of the image and sends it to the storage card

Image Sensor (CCD)

• contains light sensitive pixels and measures the light energy striking each pixels

• Bayer filter sits on top of it, and allows certain pixels to only measure certain colours of light wave.

• Each pixels only reads 1 color, and it weighs out the light to determine color

2 types of sensors

• CCD (charged couples device)

  • horizontal and vertical row of charge capacitors.

  • analog charge from pixels is shifted through the sensor and then converted to a digital signal at a single output.

• CMOS (Complimentary metal oxides semi-conductor)

  • Each pixel has converts its own analog signal to digital signal locally. no charge shifts across the sensor

Analog to digital convertor

• as light hits the pixels, an electrical charge is created and a measure in the change of voltage is recorded at each pixel site.

• The data collected is then converted to a digital signal

Circuit board

Carries the data from a CCD and stores it in a memory card

Composition of Digital camera

Image sensor (CCD), Bayer Filter, Analog to Digital converter (ADC), Circuit Board, Display screen

Science Working Group on Imaging Technology

• SWGIT

• goal is to ensure the successful introduction of forensic images in a court of law.

Section 1.4 of SWGIT

Digital imaging is an accepted practice in Forensic science, law enforcement, and the court

Section 2.1 of SWGIT

• Image capturing device should render an accurate representation.

• different applications will dictate different standards of accuracy

Digital camera allows:

• Interchangeble lens

• manual override for exposure and focus

• off camera flash

• remote shutter release

• tripod mount

Make up of DSLR

mirror, shutter, sensor, focus screen, pentaprism, viewfinder eyepiece

Zoom Lens

• Has variable focus lengths (24-70mm, 18-55mm)

• ex. a telephoto lens

Fixed lenses

• Fixed focal lengths

• ex. Macro lens, Wide angle lens

Remote shutter release

Communicated with camera via radio waves, allows one to take a photo without physically having to press the shutter release button

Tripod mount

Allows for camera stability and prevent camera shake during long exposures. Always used during night scenes.

SD cards

Memory cards in various sizes. (sony,, Lexar, Toshiba, San Disk)

Image compression

• Section 2.2 in SWGIT

• the process of reducing a digital file size

• lossy or lossless

• decisions depends by the intended use of the image.

JPEG - Joint Photographic Experts Group

• Lossy compression - information is lost permanently

• Computer looks at what can be discarded based on algorithms of neighboring pixels

• Removes colour pixels and adds unwanted artefacts

• Used in forensic science for court purposes

Pros of JPEG

• Maximum number of photos before a memory card is full

• Fastest in camera processing

• compatible with all types of computer systems

• small file size - easy to transfer and send across platform

Cons of JPEG

• 8×8 pixel blacks (low resolution)

• Lossy format so image data is loss during compression

• the higher the level of compression the more information lost

• everytime it is modifed and saved it goes through compression and loses more data

TIFF - Tagged information file format

• Images can be compressed and uncompressed using lossless compression

• Images can be edited and re-saved without compromising quality

• Takes information away, stores it then re-adds it once the file is reopened

Pros of TIFF

• high quality (16 bits)

• Does not require post processing

• Lossless format - so images can be enhanced and resaved without compression

Cons of TIFF

• large files created resulting in long in camera processing'

• Requires large memory cards to store images

• Files take up storage on computers.

Pros of RAW

• All original details stays with the image for future needs

• 12-bit

• The camera does not fix brightness, contrast, or sharpness

• Used for analysis/comparison purposes in Forensics

Cons of Raw

• NO industry standard for RAW formats, each manufcature have their own format

• Not compatible with mainstream computers so it needs to be converted to JPEG or TIFF

BIT Depth

• # of tones between the pure dark and pure light

• # tones represents each channel and the different color combination

• Impacts resolution (more color combinations —> better resolution)

Front parts of Camera

• Lens

• lens release button

• autofocus mode

• actviate in camera flash

• Subcommand dial

• mode Dial

Top parts of Camera

Power switch, metering mode, record, shutter release, Diopeter,m

Rear parts of Camera

• pay back button

• delete button

• speaker

Lens Anatomy

• Zoom ring

• selected focal lengths

• Lens information

• manual/auto focus switch

• focus ring

focal length

• The distance between the lens and image sensor when the subject is in sharp focus.

• optical distance where light rays converge to form a sharp image on the sensor

Depth of field

• How much within the image is in focus.

• The distance between the farthest and the nearest object which can all be brought into acceptable focus.

Field of view

How much can you get in the picture

Focal length and field of view

• short focal length = wider field of view and lower magnification (you see more)

• long focal length = narrow field of view and higher magnification (closer up image)

• 50mm focal length is favourable

• 85 mm is good for human face

Exposure

• good **** is recording a full scale of tones from detail in the dark area to the detail in the light areas.

• Can be controlled via shutter speed and aperature

• Histograms tells you if you need to adjust it.

Historgams

• graphical representation of the pixels exposed in your image

• Left side = black/shadows

• right = white/light

• middle = grey/midtones

• looks for an even disturbution across the scale

ISO- international standards organization

• measures the sensitivity of the sensors to light

• increasing this, increases sensitivity to light (needed when in the dark)

• But increasing this, increases background noise, and introduced a grainy pic

Aperature

• The size of the opening of the lens

• controls the amount of light that reached the sensor

• expressed in f-stops

• high f-stops - small opening - less light

• low f-stop - large opening - more light

aperature and depth of feild

• higher f-stop —> deep DOF

• Lower f-stop —> shallow DOF

Greatest DOF

• greatest f-stop

• shorter focal length

Shutter Speed

• A device that controls the length of time light is allowed to travel to the sensor.

• expressed as a fraction of a secons or several seconds

Use a tripod

• 1/60 is the minimum, anything lower (1/30,1/15,1/8) requires this.

• upon changing lens, the reciporical of the maximum focal length is then the minimum value to use this.

Rule of reciprocity

How aperture and shutter speed work together to achieve proper exposure of an image

• If you decrease shutter speed (more time open), you have to increase f-stop (less light)

• If you increase shutter speed (less time open), you decrease f-stop (more light in)

Crime scene photography

general: zoom lens, 50 mm, f8, ISO 400-800

1. ID photos

2. Scene Establishing

3. Evidence establishing

4. Close ups

Scene establishing

• street sign or pathways heading up to the scene

• Building #, apartment #, unit #

• Overall shots of 4 corners of the scene

Evidence establishing

• Overall and midrange of item of interest with an identifier marker

Close ups

• macro, 105 mm, f-16, ISO 100

• of the item of interest, and can move item for this after evidence establishing (overall & midrange).

• Captures a more detailed and accurate image of item.

• should fill the frame and include a scale.

Note taking

• Who, where, when?

• independent recollection of events or scene - do not corroborate

• discuss only factual details

Why note taking

• memory incase testifying in court

• make available for everyone to see

• let supervisors and managers know what you did

Do’s notetaking

• Underline the date

• 24 hour times

• list: arrival date, started taking photos, scene completion

• dont leave empty lines/spaces

• use ink (black)

• cross out mistakes with a single line a write your initials.