Image processing 1 Flashcards
What is a digital image?
A number of discrete picture elements called pixels
Each pixel has a ….?
(Unique) Digital Number
What does a DN represent?
The radiance measured in that pixel in that spectral band
What are the ways to interpret an image?
Tone
Size
Shape
Pattern
Texture
Shadow
Combination of different colours provide….
Secondary or tertiary colours
What is a true colour composite?
When the image and the display band are both in the RGB wavelengths e.g Red is red, blue is blue
What is a false colour composite?
When the image and the display band are in different wavelengths
NIR in red, red in green and green in blue wavelengths
Why is red often used to display vegetation?
The human eye is more receptive to it
What is an image histogram?
A graphical representation of the number of pixels (frequency) in an image as a function of their brightness values (DN)
What would the pixel composition of a dark image be?
Lots of pixels have low reflectance
What would the pixel composition of a bright image be?
Lots of pixels have high reflectance
What would the pixel composition of a low contrast image be?
Lots of pixels concentrates in one small waveband area
What would the pixel composition of a high contrast image be?
Pixels are spread across lots of different wavelengths
How does image enhancement work?
Improve the way the image is displayed
Not changing the pixels themselves, just how they are displayed
What is contrast stretching?
When you expand the original input brightness to make it the same as the total dynamic range
