This is easy to use and powerful Utilitaire for batch conversion of image files using scripts.
The following actions available when writing the script: resize, crop images; rotate, mirror images; change color resolution; change image's brightness, contrast, and gamma; change color balance using the filters, which operate in RGB, CMY, YCbCr, HLS, and HSV color spaces; modify images using the sharpen, detail, smooth, blur, and contour effects; add transparency watermarks and borders; replace one color with another; convert images to BMP, JPG, GIF, PBM, PGM, PNG, PPM, TGA, TIF image formats; rename converted files