Creating a false-colour composite image with an image that contains an extra band of information (alpha channel) is best done with Geographic Imager Channel Management.
1.In Adobe Photoshop, browse to the Landsat 7 Multispectral folder and open All bands.tif.
This image has all the Landsat bands (channels) already merged into it. You’ll use Geographic Imager Channel Management to create a false-colour composite.
2.On the Geographic Imager panel, click the Channel Management button.
The current Colour Mode is Grayscale Colour which explains why the image is displayed as such.
3.Choose RGB Colour from the Colour Mode drop-down list and click OK.
The Gray Band is assigned a channel role of Red, Band 2 is assigned Green, and Band 3 is assigned Blue. You’ll change the visibility of the Gray Band and reassign the channel roles for bands 2, 3, and 4 to create the correct false-colour composite appearance.
4.Click the Channel Management button and click the Visibility check box for Gray Band to disable it. Click the Visibility check box for Band 4 to enable it. Click OK.
The Channel Management also takes into account roles of available alpha channels.
5.Click the Channel Management button and click the Band 4 Channel Role (it is set as Alpha 1) and choose Red in the drop-down list. Change the Band 3 Channel Role to Green. The Band 2 Channel Role should automatically update to Blue.
6.Click OK to confirm the reassignment of channels.
A false-colour composite image using Channel Management is created. These changes are reflected in the Geographic Imager Channels panel.