Tone
Also called: Colour in image interpretation · Topic: Remote Sensing, GIS and GNSS · NCERT: Class 11, Ch 6 "Introduction to Remote Sensing"
Meaning
Tone is the shade of grey, or the colour, in which an object appears in an image. It depends on how much energy the object reflects in the band being recorded. More reflected energy gives a lighter tone and less gives a darker tone. Tone is the most basic clue in visual interpretation. Smooth, dry surfaces look light and fresh water looks dark. In a standard false colour composite, healthy vegetation looks red.
Example
In NCERT's images of Sambhar Lake, Rajasthan, clear water absorbs red and near-infrared energy, so it looks dark. Turbid (muddy) water reflects more blue and green light, so it looks light.
Don't confuse with
- Texture: how often the tone changes over a small area, from fine to coarse. It is not the tone itself.
- Shadow: the dark area cast by a tall object. It is not caused by what the object's surface reflects.
Related concepts
- Aerial photograph
- Digital image
- Pixel
- Digital number
- Digital image processing
- False colour composite
- Visual image interpretation
- Elements of visual interpretation
- Texture
- Shadow in image interpretation