Didger exports TIF files in uncompressed format. Uncompressed files will be much larger than compressed files.
You can estimate the uncompressed file size in bytes by multiplying the number of pixels (width) by the number of pixels (height) times by the Color Depth. The Color Depth value is 3 for True Color, 1 for 256 Colors, or 0.125 Monochrome.
For example, if your image is 3000 x 3000 pixels and you export in 256 Colors, the resulting file size would be about 9 MB (3000x3000x1).
To reduce the exported TIF file size, you can either 1) reduce the pixel count being exported or 2) reduce the Color Depth.
Updated October 20, 2016