Image Bands

Many raster files, including color digital photos, are made up of multiple bands or layers. You can think of image bands (also called channels or layers) as a collection of images taken simultaneously of the same place. Many sensors on earth observing satellites measure the amount of electromagnetic radiation (EMR) that is reflected or emitted from the Earth’s surface. These sensors, known as multispectral sensors, simultaneously measure data in multiple regions of the electromagnetic spectrum. The range of wavelengths measured by a sensor is known as a band and are commonly described by the name (Red or Near-IR for example) and the wavelength of the energy being recorded.

Human vision is a system that is able to detect three wavelengths or spectral bands. Our brains combine this data detected by our eyes into a single color image. All of the colors that humans perceive can be created by mixing the three additive primary colors: red, green and blue. This is also the basis of color imaging, including analog film and digital display screens.

Color images are actually made up of three values, one each for the amount of red, green, and blue light that entered your camera for each pixel. This means a "3-band" image is needed to display a color image.

Modern computer monitors use red, green and blue light emitting diodes (LEDs) to produce the full range of colors. Each pixel on the screen can display a combination of red, green and blue light. In what's known as a true-color monitor there are 24-bits of color data per pixel. Each color (red, green, blue) is 8-bits, meaning there can be 256 (2⁸) possible color shades for each color. Since each color has 256 shades, we can multiply 256 (for red) by 256 for green by 256 for blue to get: 256 x 256 x 256 = 16,777,216 colors (the same as 2²⁴ or 24-bit). The result is a color image where each pixel’s color is determined by a combination of RGB in different brightnesses. Use the below slider tool to see how changing the amount of each primary color changes the final output color.

Mulitspectral Data

A standard color digital camera collects data for three bands in the visible spectrum (red, green and blue). Sensors that collect data across multiple parts of the electromagnetic spectrum are known as Multispectral sensors. These sensors, simultaneously measure data in multiple regions of the electromagnetic spectrum, often including visible light, near and short wave infrared.

Landsat 8 Reflective Bands

Landsat 8 records different ranges of wavelengths along the electromagnetic spectrum. Each of these ranges is known as a band and in total Landsat 8 has 11 bands. The first 7 of these bands are in the visible and infrared portion of the spectrum and are commonly known as the "reflective bands". These are recorded by the Operational Land Imager (OLI) on board Landsat 8, which collects data on the amount of light that is reflected off of the Earth's surfaces. In addition to the 7 bands listed in the table above, there is also a panchromatic or black-and-white band (Band 8) and a cirrus cloud band (Band 9) that is used to detect cirrus clouds. Landsat 8 also has a seperate Thermal Infrared Sensor (TIRS) which collects data in two thermal infrared bands. Read more about Landsat 8 Bands.

Explore Pixel Values in Color Images

Color photos are actually made up of three values, one each for the amount of red, green, and blue light that entered your camera for each pixel. This means we need a "3-band" image to display color. Move your mouse cursor around the image below to see the values. Note that the top value is the value for red, the middle value is for the amount of green, and the bottom value is for the amount of blue. Note: You may need to hit "Refresh" on your browser for the image to load.

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