False-Color Composite with Multiple Images Tutorial – Avenza Systems

Another powerful remote sensing tool in Adobe Photoshop is the ability to create a false-colour composite image. Multispectral images contain information inside and outside the visible electromagnetic spectrum. To use this information, the wavelengths outside the visible spectrum need to be reassigned to the visible spectrum so that it is visible to the human eye. This tutorial will create a false-colour composite of downtown Toronto and surrounding suburban areas.

Often multispectral satellite images will consist of several grayscale images, with each image containing one of the wavelengths or bands of the electromagnetic spectrum. These images need to be combined into one image. The Adobe Photoshop function called Merge Channels merges images to create false-colour or true-colour composites. You may easily identify distinct features by their unique spectral signature.

1.In Adobe Photoshop, browse to the Landsat 7 Multispectral folder and open the following images:

Band 2 (Green), 30 meters.tif
Band 3 (Red), 30 meters.tif
Band 4 (Near Infrared), 30 meters.tif

information When creating false-colour composites, images must be of the same image resolution and have the same spatial extents. If the images need to be cropped, it is recommended to use the Geographic Imager GeoCrop function to assure that the extents of the images remain consistent.

2.From the Windows menu, choose Channels to open the Channels panel.

3.In any of the active document windows, click Merge Channels in the Channels panel options menu.

false-color_mergechannels

4.In the Merge Channels dialog box, choose RGB Colour in the Mode drop-down list and ensure there are 3 channels. Click OK.

false-color_mergergb

5.In the Merge RGB Channels dialog box specify the following channels:

Red: Band 4 (Near Infrared), 30 meters.tif
Green: Band 3 (Red), 30 meters.tif
Blue: Band 2 (Green), 30 meters.tif

false-color_mergergbchannels

6.Click OK to complete the merge.

information A reference file called Untitled-x.tfw (the x value may change depending on if you have other reference files named something similar) is created in the default reference format specified in the Geographic Imager Preferences dialog box.

false-color_complete

A false-colour composite image with georeferencing is created. The band combination chosen makes vegetation appear in shades of red because vegetation reflects a lot of near-infrared light. The brighter the red, the healthier the vegetation. Urban areas appear blue-grey. The bright red areas at the top of the image belong to the prestigious Rosedale Golf Club.

More about Landsat 7 band combinations

R,G,B	Description
3,2,1	The “nature colour” combination. It provides the most water penetration.
4,3,2	Standard “false-colour” combination. Vegetation shows in red.
7,4,2	The “nature-like” combination. Sand, soil and minerals show in multitude of colour. Fires would appear in red. It provides clear imagery in desert region.
7,5,3	The “nature-like” combination. Sand, soil and minerals appear in variety of colour.
5,4,1	Good for agricultural studies. Healthy vegetation shows in bright green colour.
7,5,4	Provides best atmospheric penetration. Vegetation shows in blue. Useful for geological study.
7,3,1	Rocks may appear in variety of colour. Good for the geological study.

information Some multispectral images may be provided as a single image that stores extra channels (called alpha channels in Adobe Photoshop). To create false-colour composites from these images in Adobe Photoshop, the channels must first be split into single gray scale images (Channels panel option menu > Split Channels). Then channels can be merged and reordered as described above.

Want to follow along to this tutorial?

Please see our corresponding YouTube videos for the various Geographic Imager tutorials covered in our online documentation!*

* Providing a general overview of the steps covered in this tutorial, our False-Color Composite with Multiple Images video tutorial will walk you through the false-color composite creation process in Geographic Imager.