I converted a bunch of "normal" JPG photos via
convert infile -colorspace Gray outfile
to monochrome. However the result is for all images very dark. Here a sample conversion: original photo and converted monochrome image.
Is there a better way to convert a photo-realistic image with ImageMagick to gray-scale?
The documentation states that when changing the color space, the colors are converted from their original gamma to linear before the conversion. You need to convert them back to an appropriate gamma.
convert infile -colorspace Gray -gamma 2.2 outfile
来源：https://stackoverflow.com/questions/15399653/image-conversion-to-grayscale-using-imagemagick-is-very-dark