If you have a script-based installation, InstallScript or InstallScript MSI, the image format you choose for your installation splash screen is important.
Splash screens can be added to the Splash Screen section of the Support Files view. In that section is a Language Independent folder and a folder for each language your installation supports.
The Splash Screen section of the Support Files View
In the above screenshot, you see that I have opened an InstallScript MSI project to the Support Files view. In this project I have added a .bmp splash screen to the Language Independent folder. Also, my installation only supports English, which is why I just made one version of the splash screen. Since my splash screen is in English, I could have put it in the English folder, but I chose to put it in the Language Independent folder.
Here’s the important part. If you are using a pure InstallScript project, you can use .bmp or .gif files as splash screens. If you are using an InstallScript MSI project, you can only use .bmp files as splash screens.
What about Basic MSI projects? For those, you should use a .bmp splash screen.