LIghtburn does a pretty good job of translating color images to grayscale, but I’ll add that there are times when I prefer to process an image through GIMP instead to convert color to grayscale.
An example would be an image that has several different colors but when converted to grayscale perhaps 2 of the colors end up nearly the same shade of gray and you would like more contrast between them, especially if it’s 2 adjacent colors and you want to try and vectorize the image. In GIMP you can use the Hue-Saturation tool to desaturate the image and then change the lightness on 6 different color channels until you like the contrast between your shades of gray.
GIMP just gives more control over the process if you need it.
This tool is very handy for fine manipulation of grayscale images:
