The following formats are the currently supported Image Optimization formats

• RasterImageFormat.Jpeg, Bits per pixel: 8 for grayscale, 24 for color.
• RasterImageFormat.Jpeg411, Bits per pixel: 8 for grayscale, 24 for color.
• RasterImageFormat.Jpeg422, Bits per pixel: 8 for grayscale, 24 for color.
• RasterImageFormat.ExifJpeg411, Bits per pixel: 24 (color only).
• RasterImageFormat.ExifJpeg422, Bits per pixel: 24 (color only).
• RasterImageFormat.Gif, Bits per pixel: 1, 2, 3, 4, 5, 6, 7, and 8.
• RasterImageFormat.Png, Bits per pixel: 1, 4, 8, 24, and 32.
• RasterImageFormat.Bmp, Bits per pixel: 1, 4, 8, 16, 24, and 32.
• RasterImageFormat.BmpRle, Bits per pixel: 4, and 8.

Reference