If an imported Targa file seems distorted in GenCG, the alpha channel was probably not created within Adobe Photoshop®.
With Adobe Photoshop® CS series and CC 2015, you will need to create an alpha channel for 3rd party software, such as GenCG, to read the image properly. Versions of Adobe Photoshop® before the CS line will create and save alpha channels within your Targa file automatically.
Please follow these steps to create an alpha channel:
Open the image you created in Adobe Photoshop®. If it has multiple layers and you see the transparent background, merge your image by going to [Layer] > [Merge Visible]. If you do not see a transparent background, select the Eraser or Magic Eraser tool and delete the background after you've flattened the image.
Locate the flattened layer on your Layers palette and select the transparency of the image by holding CTRL and left-clicking on the layer. This will create a marquee around the image.
While the marquee is still around the image, bring up your Channels palette and create a new channel by clicking the [New Channel] button at the bottom of the palette.
You will now see five channels: RGB, R, G, B, and Alpha 1. Select Alpha 1 and make sure every other channel is turned off.
Select white as your foreground color on your main toolbar and fill the selection of the alpha channel by going to [Edit] > [Fill]. Make sure you set the Content Fill to [Foreground color] with [Normal] selected for the Blending Option and Opacity set to [100%].
Save the image as a 32-bit Targa file and import the Targa file into GenCG.