A digital image is composed of a two-dimensional grid of pixels, where each pixel represents an area on the ground and has an intensity value and location address. Both digital images and analog photographs can be represented this way. Digital images have higher spatial, spectral, and radiometric resolutions than analog photographs, allowing for more detailed analysis. Aerial photographs can be analog, captured on film, or digital. Common film types include color, color infrared, black and white, and video films suited for different remote sensing applications.

1. Image Characteristics
&
Aerial Photographic
Films

2. ● What is an Image?
– Any pictorial representation, regardless of what wavelengths or RS device has
been used to detect and record the electromagnetic energy
– A photograph refers specifically to images that have been detected as well as
recorded on photographic Film
• Based on these definitions, we can say that all photographs are images, but not
all images are Photographs
•The images may be analog or digital.
•Aerial photograph are examples of analog images while satellite images
acquired using electronic sensors are examples of digital images.

3. Pixels
A digital image comprises of a two dimensional array of
individual picture elements called pixels arranged in columns
and rows.
Each pixel represents an area on the Earth's surface.
 A pixel has an intensity value and a location address in the
two dimensional image.
•The intensity value represents the measured physical quantity
such as the solar radiance in a given wavelength band reflected
from the ground, emitted infrared radiation or backscattered
radar intensity. This value is normally the average value for the
whole ground area covered by the pixel.
•The address of a pixel is denoted by its row and column
coordinates in the two-dimensional image.

4. A digital image is a two-
dimensional array of pixels. Each
pixel has an intensity value
(represented by a digital number)
and a location address (referenced
by its row and column numbers).
A photograph could also be represented and
displayed in a digital format by subdividing the
image into small equal-sized and shaped areas,
called picture elements or pixels, and
representing the brightness of each area with
a numeric value or digital number.

5. Analog vs. Digital photographs
• Analog : traditional photograph or photograph like images, i.e. – a physical
record – a paper or film with chemical coatings that portray the pattern of the
images
– Brightness of a photograph are proportional (i.e. analogous) to the brightness in
a scene
– Disadvantages: storage, transmission, searching and analysis
• Digital photographs: acquired using electronic technologies that record image
information as arrays of individual values (pixels – recorded photons reflected or
emitted from individual patches of ground) that convey the pattern of discrete
brightness within an image
• Its design differs significantly than that of Analog cameras
• Detectors: charged-coupled devices (CCDs) or complementary metal oxide
semiconductor (CMOS)

6. Characteristics of Digital Image
There are three basic measures for digital image characteristics:
• spatial resolution
• spectral resolution and
• radiometric resolution.
 higher the resolution of an image, the more information the image
contains

7. Characteristics of digital image
•Spatial resolution refers to the size of the smallest object that can be resolved
on the ground. In a digital image, the resolution is limited by the pixel size, i.e.
the smallest resolvable object cannot be smaller than the pixel size.
A "High Resolution" image refers to one with a small resolution
size. Fine details can be seen in a high resolution image.
On the other hand, a "Low Resolution" image is one with a large
resolution size, i.e. only coarse features can be observed in the
image.
• Spectral resolution refers to the ability of a satellite sensor to measure
specific wavelengths of the electromagnetic spectrum. The finer the spectral
resolution, the narrower the wavelength range for a particular channel or
band.
•Radiometric Resolution refers to the smallest change in intensity level that
can be detected by the sensing system. The intrinsic radiometric resolution
of a sensing system depends on the signal to noise ratio of the detector.

8. Digital photographs - Advantages
• Direct analytical processing, greater range of brightness, more interpretation keys
• Storage, processing and transmission of data – more convinient and economical
• Variety in the application and range of products derived from digital photographs
• True multispectral coverage

9. .
Aerial Photographs – Two Major Types
•Vertical : the survey camera lens points vertically downwards producing a view
resembling a plan of the ground
• Oblique : the survey camera lens axis points at an angle to the ground. If the
horizon is included, the photograph is defined as a high oblique; if not, it is a low
oblique.

10. Types of Aerial Photographic Film
• Color transparency film
• Color negative film
• Color infrared film (CIR = NIR+G+R)
• Color video film
• Black and white film

11. Types of Aerial Photographic Film
• Color transparency film- used for depth penetration, location of subsurface
features
– less expensive than color negative film which
requires the production of paper prints
– good resolution (detail)
– excellent visual presentation aid
• Color negative film, used for land typing. The
color prints produced from this film are:
easy to use in stereoscope
excellent text illustration
• Color infrared film, used for shoreline
classification, vegetation analysis, water
– excellent for comparison with normal color films

12. Types of Aerial Photographic Film
Color video film, used for depth penetration
– quick turnaround and relatively cheap
– suitable for monitoring dynamic parameters
•Black and white film, used for land typing
(acquired in the NIR region)
The black and white prints from this film are:
– free of atmospheric scattering
– less expensive than colour prints
– useful for general coastal studies
– easy to reproduce
– make excellent base maps