Image colors (binary, gray, RGB)

1. Prof. Dr.Abbas H.Prof. Dr.Abbas H. HassinHassin AlasadiAlasadi
Email : abbashh2002@gmail.comEmail : abbashh2002@gmail.com

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Review of Lecture 1Review of Lecture 1
This lecture will cover:
 Colors of image.
 The human visual system
 Light and the electromagnetic spectrum
 Image representation
 Image sensing and acquisition
 Sampling, quantisation and resolution

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Review of Lecture 1Review of Lecture 1
An image is: a two-dimensional function f(x, y)
of intensity (gray or color) values, where x
and y are spatial (plane) coordinates.
The intensity or gray level of the image at
that point is the amplitude of (f) at any pair
of coordinates (x, y).
Pixel : is the term most widely used to denote
the elements of a digital image.

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Review of Lecture 1Review of Lecture 1
Image F(x,y)

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Image ColorImage Color
1. Binary Image (Black and White)
Black and White contains only one value (0 or 1).
2. Gray scale image
Gray image represent by black and white shades of
gray without apparent color or combination of
levels for example: (8-bit) gray image means total
(28
) levels form black to white, black =0 and
White = 255.

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Image ColorImage Color
3. Red, Green, and Blue)
 Images represented in the RGB color model
consist of three component images – one for each
primary color.
 When fed into a monitor these images are
combined to create a composite color image
 The number of bits used to represent each pixel is
referred to as the color depth.
 A 24-bit image is often referred to as a full-color
image as it allows (28
) 3
= 16,777,216 colors.

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Image ColorImage Color
4. Red, Green, and Blue, + “Alpha” or Opacity)
RGBA stands for Red, Green, and Blue Alpha.
Here “A” in this property name stands for
“Alpha”. This additional feature can be used to
specify an opacity value for any color.

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Image ColorImage Color
Black and whiteBlack and white
Grayscale RGB RGBA

9. Human Visual SystemHuman Visual System
 The best vision model we have!
 Knowledge of how images form in the eye can help
us with processing digital images
 We will take just a rapid tour of the human visual
system
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10. Structure Of The Human EyeStructure Of The Human Eye
The lens focuses light from objects onto the retina
The retina is covered with
light receptors called
cones (6-7 million) and
rods (75-150 million)
Cones are concentrated
around the fovea and are
very sensitive to colour
Rods are more spread out
and are sensitive to low levels of illumination
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Image Formation In The EyeImage Formation In The Eye
Muscles within the eye can be used to change the
shape of the lens allowing us focus on objects that are
near or far away
An image is focused onto the retina causing rods and
cones to become excited which ultimately send signals
to the brain

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Brightness Adaptation & DiscriminationBrightness Adaptation & Discrimination
The human visual system can perceive approximately
1010
different light intensity levels
However, at any one time we can only discriminate
between a much smaller number – brightness
adaptation
Similarly, the perceived intensity of a region is related
to the light intensities of the regions surrounding it

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Brightness Adaptation & DiscriminationBrightness Adaptation & Discrimination
An example of Mach bands

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Light And The Electromagnetic SpectrumLight And The Electromagnetic Spectrum
Light is just a particular part of the electromagnetic
spectrum that can be sensed by the human eye
The electromagnetic spectrum is split up according to
the wavelengths of different forms of energy

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Reflected LightReflected Light
The colours that we perceive are determined by the
nature of the light reflected from an object
For example, if white
light is shone onto a
green object most
wavelengths are
absorbed, while green
light is reflected from
the object

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Images fromDifferent EMRadiationImages fromDifferent EMRadiation
1. Radar imaging (radio waves)
2. Magnetic Resonance Imaging (MRI) (Radio waves)
3. Microwave imaging
4. Infrared imaging
5. Photographs
6. Ultraviolet imaging telescopes
7. X rays and Computed tomography‐
8. Positron emission tomography (gamma rays)
9. Ultrasound (not EM waves)

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Image File FormatsImage File Formats
There are Hundreds of image file formats some of them as
following:
1.Tagged Image File Format (TIFF):is lossless which is
considered the highest quality format for commercial work.
2.Graphics Interchange Format (GIF):was designed by
CompuServe (CompuServe: was the first major
commercial online service in the United States) in the
early days of computer 8-bit video, before JPG, for video
display at dial up modem speeds.

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Image File FormatsImage File Formats
There are Hundreds of image file formats some of them as
following:
3.Portable Network Graphics (PNG): can replace GIF today
(web browsers show both), and PNG also offers many options of
TIF too (indexed or RGB, 1 to 48-bits, etc).
4.Joint Photographic Experts Group (JPEG): is the most used
image file format. Digital cameras and web pages normally use
JPG files
5.Bitmap (BMP): is a raster graphics image file format used to
store bitmap digital images, independently of the display
device (such as a graphics adapter).