I have a 4 band image (Blue, Green, Red and Near Infrared). If I display my image with only the green band in the RGB channel, the image displayed is panchromatic.

Why is that?

  • $\begingroup$ If you use only one channel, what do you expect? $\endgroup$ – Christoph Oct 27 '18 at 6:10
  • $\begingroup$ But would RGB not be assigned to each of the bands intensity? I say because in another case I am displaying Band 2 twice and Band 3, and the resultant image has color. $\endgroup$ – Chayan Lahiri Oct 27 '18 at 21:39
  • $\begingroup$ Do you really mean panchromatic, or do you mean monochromatic? Also, what are you using to display the file? I could imagine some software being able to simulate a panchromatic sensor from a multiband image. $\endgroup$ – Deditos Oct 30 '18 at 9:04
  • $\begingroup$ You are right, I meant monochromatic. Just to clarify I displayed band 3 in all three channels to get monochromatic image, however, when I displayed band 3 in two channels with band 2 in the third arcmap displayed color. $\endgroup$ – Chayan Lahiri Oct 30 '18 at 17:11

An RGB image can not be rendered if you only supply information for one color channel. This is because three channels are needed: Red, Green and Blue. Different software will deal with this invalid input in different ways: Some might set the remaining channels as black (i.e. filling with zero values). In that case the resulting image will be monocromatic. In shades of green in your example.

Other software might fill the missing channels with the same information supplied for the available one. In that case the result is a gray scale version of the band supplied.

In a general case, the rendered image will only display varying colors if two or more channels contain different information (i.e. different bands).

As mentioned in the comments, it is important to note that the difference between monocromatic and pancromatic. The former is a general term used to describe images formed by shades of a single color. While the latter is a specific term used in multispectral sensors to denote a band with a wider spectral response, and that usually have also higher spatial resolution.

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