Digital Frame Camera

We will cover the following topics in this post:
  • What is Digital Frame Camera?
  • Image Sensors-CCDs and CMOS
  • Digital Frame Camera Data Collection
  • Filtration
  • Timeliness
  • Digital Sensor System

What is Digital Frame Camera?

Digital camera records and stores photographic images in digital form. Many current models are also able to capture sound or video, in addition to still images. Capture is usually accomplished by use of a image sensor, using a charged coupled device (CCD). These stored images can be uploaded to a computer immediately or stored in the camera for to be uploaded into a computer or printer later. Images may also be archived on a photographic compact disc or external hard disk. Steven Sasson, an engineer at Eastman Kodak, invented and built a self-contained electronic camera that used a charge-coupled device(CCD) image sensor in 1975.

Image Sensor-CCDs

The charge-coupled-device was invented in the late 1960s by scientists at the Bell Labs. It was originally conceived as a new type of computer memory circuit, but it soon became apparent that it had many other applications, including image data collection, because of the sensitivity of silicon to light.

A matrix of CCDs (referred to by Kodak, Inc., as photosites) represents the heart and soul of digital frame cameras that are now being used to collect remote sensor data.

CCD sensor's role in the digital image capture process (Kodak, 1999):

1. Mechanical shutter opens, exposing the CCD sensor to light.

2. Light is converted to a charge in the CCD.

3. The shutter closes, blocking the light.

4. The charge is transferred to the CCD output register and converted to a signal.

5. The signal is digitized and stored in computer memory.

6. The stored image is processed and displayed on the camera's liquid crystal display (LCD), on a computer screen. or used to make hard-copy prints.

Digital Frame Camera Data Collection

In a digital frame camera, the standard photographic silver-halide crystal emulsion at the film plane is replaced with a matrix (area array) of CCDs. There are usually thousands of light-sensitive photosites (pixels) that convert varying incident wavelengths of light into electrical signals.

An image is acquired when incident light (photons) falls on the array of pixels. The energy associated with each photon is absorbed by the silicon, and a reaction takes place that creates an electron-hole charge pair (e.g., an electron). The number of electrons collected at each pixel is linearly dependent on the amount of light (photons) received per unit time and nonlinearly dependent on wavelength.

The geographic area of the terrain recorded by the CCD area array is a function of I) the dimension of the CCD array in rows and columns, 2) the focal length of the camera lens (the distance from the rear nodal point of the lens to the CCD array), and 3) the altitude of the aircraft above ground level.

Increasing the actual size (dimension) of the CCD array will record more geographic area if all other variables are held constant. For example, doubling the size of the CCD array from I 000 x 1000 to 2000 x 2000 will record four times as much geographic area during the same exposure.

Moving the aircraft with the frame camera closer to the ground results in higher spatial resolution but less geographic area coverage.


Color Filter Array(CFA) patterns are used to capture the incident blue, green, and red photons of light. A number of CFAs have been invented, but only three are discussed here.

RGB filter wheel CFA- A filter wheel is mounted in front of a monochromatic CCD sensor. The CCD makes three sequential exposures-one for each color. ln this case, all photosites on the CCD area array capture red, blue, or green light during the appropriate exposure. it is suitable for still photography.

Three-Chip-Cameras - Use three separate full-frame CCDs, each coated with a filter to make it red, green, or blue-sensitive. A beam splitter inside the camera divides incoming energy into three distinct bands and sends the energy to the appropriate CCD. This design delivers high resolution and good color rendition of rapidly moving objects. It is the preferred method for remote sensing data collection.

A single-chip technology - Filter captures all three colors with a single full-frame CCD. This is performed by placing a specially designed filter over each pixel, giving it the ability to capture red, green, and blue information.


One of the most important characteristics of digital camera remote sensing is that the data are available as soon as they are collected. There is no need to send the imagery out for chemical processing and then wait for its return.

If desired, the digital imagery can be downlinked electronically to the ground while the aircraft is still in the air. Further more, the cost of photographic processing is removed unless one wants to make hard-copies.

Anyone can point a digital camera out the window of a plane and obtain oblique aerial photography. It is quite another matter to obtain quality digital aerial photography for photogrammetric or remote digital image processing applications.

This requires the use of a digital frame camera system such as the Digital Sensor System developed by Emerge, Inc.

Digital Sensor System

The Digital Sensor System (DSS) developed by Emerge Inc., uses a proprietary digital camera area array configuration that acquires vertical imagery containing 4092 x 4079.

Each pixel in the area array is 9 x 9 microns. Users can specify color (blue, green, and red) or color-infrared (green, red, and near-infrared) multiband imagery in the spectral region from 0.4 to 0.9 μm.

The data may be recorded at 8 or 16 bits per pixel. Emerge collects real-time differentially corrected GPS data about each digital frame of imagery.

These data are used to mosaic and orthorectify the imagery using photogrammetric techniques.

The pixel placement accuracy meets national map accuracy standards (Emerge, 2004). A variety of flying heights and different focal-length Nikon lenses can be used to obtain imagery with spatial resolutions ranging from 0.15 to 3m.