Digital number
Also called: DN, DN value · Topic: Remote Sensing, GIS and GNSS · NCERT: Class 11, Ch 6 "Introduction to Remote Sensing"
Meaning
A digital number (DN) is the value stored in each pixel of a digital image. It stands for the average energy the sensor received from that ground cell. The value falls within the sensor's range of grey levels, for example 0 to 127 for IRS LISS or 0 to 255 for Landsat TM. A low DN shows as dark and a high DN shows as bright. Computers use these numbers to correct, improve and classify images.
Example
On a near-infrared band image of Sambhar Lake, Rajasthan, clear water absorbs most of the energy, so its pixels have low DNs and look dark. Nearby dry, salty land reflects strongly, so its pixels have high DNs and look light.
Don't confuse with
- Pixel: the cell itself, with its row and column address. The DN is the brightness value stored in that cell.
Related concepts
- Aerial photograph
- Digital image
- Pixel
- Digital image processing
- False colour composite
- Visual image interpretation
- Elements of visual interpretation
- Tone
- Texture
- Shadow in image interpretation