There are may ways and many reasons to convert a color image to black and white. How it is done as to method and results depend on what you need to accomplish.

If you want a traditional or accurate gray scale representation of the colors and tones you are going for a PANCHROMATIC interpretation. If for some reason you want to increase the contrast more significantly as in a dramatic portrait, you may go for a more ORTHOCHROMATIC interpretation which would exaggerate the skin texture and darke the red in lips etc.

In digital post processing it is easier to acheive a wide variety of monochromatic interpenetrations from images originally produced in color. In color negative work, special panchromatic papers were required and theses material were not particularly easy to use. Transparencies required the production of inter-negatives which coud also be quite painstaking.

Personally, I prefer to determine, in advance, if I an going to shoot in color or black and white. I have no prejudice for one or the other- some subjects perhaps are more suited for one or the other. On certain assignments, it is not practical to shoot both separately if both are going to be required so the obvious choice is to shoot in color and convert. If I decide or are required to work in black and white I like to pre-visualize in that medium so I set the camer for monochrome or view the scene or subject through a dark green filter to get a better idea of the tonal scale and relationships. I lie to use color filters, in certain cases to separate tones and produce contrasts where certain differet colors may register in the same tone of gray id left unfiltered.

In portraiture, shooting with a ligh yellow or ligh orange filter will create a kinda "porcelain" like skin tone. Shooting with a green filter will dramatize skin textures and mimic the effect of orthochromatic film. Yellow, orange and red filter darken skyscapes.

Shoot in color, convert in a robust editor (I use Nik Silver Efex). Much more control. You decide, not the camera

With these photos, I could make whites whiter, blacks blacker, or change tonal contrast entirely, such as by applying a green filter (in my editor) on green grass to make it lighter. Red filters make blue skies darker. Using layers and layer masks allows you to make selective edits: dodge and burn to move the eye around the scene, darken the edges...options are limitless.

Shoot in color, convert in a robust editor (I use Nik Silver Efex). Much more control. You decide, not the camera

With these photos, I could make whites whiter, blacks blacker, or change tonal contrast entirely, such as by applying a green filter (in my editor) on green grass to make it lighter. Red filters make blue skies darker. Using layers and layer masks allows you to make selective edits: dodge and burn to move the eye around the scene, darken the edges...options are limitless.