Color vs B+W bit depth

[TreeofLifeStairs]

Let me know if I'm understanding this correctly. A 24 bit color image is broken up into three 8 bit channels (red, green, and blue) where as a black and white image has the full 24 bit depth to it.

If this is the case, my question is: I can take a picture with my camera in B+W and I would assume that it is using up the full 24 bit depth in the single B+W channel, but if I'm using a color photo and then converting it to B+W in post, would that image then be a true 24 bit image or really an 8 bit image? The essential question I guess I'm getting at is, is there any difference between an image that is shot in B+W from the camera vs one that is converted to B+W after the fact?

 

[KmH]

No. The B&W has only one 8-bit depth channel, not 3, 8-bit depth channels: 1 in red, 1 in green, 1 in blue (or so called 24-bit).

There can be a huge difference in a B&W (monochrome) made in the camera and a B&W made from converting a color image.

The conversion from a color image can be made using a 16-bit depth Raw file (48 bit RGB).
Doing so allows much broader and precise control of the tonality and contrast in the resultant B&W image, even if the image is output as an 8-bit depth file.

Actually almost all output has to have an 8-bit depth.
Bit Depth

 

[480sparky]

A digital B&W image is still an 8-bit (per each of the 3 color channels) image. It's just that the three color channels are always equal in each pixel.

While a color image pixel may have an RGB of 105:34:237, a B&W pixel will have RGBs like 105:105:105, 34:34:34 and 237:237:237.

An in-camera conversion is usually just a simple desaturation, and that's what you get and it's darned hard to change it much in post. Doing the conversion with the color data intact makes it much easier to get the tones you desire.