Digital image
Topic: Remote Sensing, GIS and GNSS · NCERT: Class 11, Ch 6 "Introduction to Remote Sensing"
Meaning
A digital image is an image made of a grid of tiny cells called pixels, arranged in rows and columns. Each pixel has a fixed address, which is its row and column. It also has a digital number (DN), which is the average brightness of the ground cell it covers. Computers can store, correct and analyse these numbers. If you zoom in too far, the picture breaks into separate squares and you lose information.
Example
NCERT shows Resourcesat-1 images of Najafgarh, Delhi (2005). In them, each pixel's value shows that fresh water absorbs energy in band 4 (infrared) and dry surfaces reflect strongly in band 2 (green).
Don't confuse with
- Photograph: recorded on film as a continuous picture, not as a grid of numbered cells.
- Digital image processing: the computer work done on a digital image, not the image itself.
Related concepts
- Aerial photograph
- Pixel
- Digital number
- Digital image processing
- False colour composite
- Visual image interpretation
- Elements of visual interpretation
- Tone
- Texture
- Shadow in image interpretation