Gamedev:Buildpics

The buildpic is the small picture of a unit which appears in the build menu of its constructor. It is always 96x96 pixels regardless of the format used (see below), and it must always be located in the unitpics directory.

Spring supports multiple image formats for buildpics. These formats are PCX, JPG, BMP, and DDS. By default, Spring will load unitname.pcx, where unitname is the short name of your unit. To override this and use a different format, use the Buildpic tag in the FBI file.

Here's a detailed list of the formats supported:

Requires Buildpic tag	File Extension	Color Depth	Description
No	PCX	8-bit (256 colors) Lossy (palette)	A PCX file using the Total Annihilation palette. Don't use it unless you're converting TA units to Spring and you're too lazy to make a new buildpic.
Yes	JPG	24-bit (16.7 million colors) Lossy (compression)	Your bog standard JPEG file. Not recommended since the compression decreases image quality.
Yes	BMP	24-bit (16.7 million colors) Non-Lossy	A standard Windows bitmap file. Recommended because of the high color depth and no loss due to compression or palette.
Yes	DDS	24-bit (16.7 million colors) Slightly Lossy (compression)	Nvidia's DirectX-enabled .dds format. This is how the maps in Spring are stored. It offers compression, but it can be lossy. It is also difficult to work with. BMP is still recommended.