How to convert 24 bit jpeg to 8 bit grayscale format?

One of the simplest and often most effective ways to get the color out of a color photo is to convert it to Grayscale -- a common option in image editing software. When converting an RGB color image to grayscale all the color is replaced with shades of gray. The image is no longer in RGB.
Inkjet printers like RGB so you can sometimes achieve better print results if you convert the image back to RGB after going grayscale - it will still be shades of gray.

Corel Photo-Paint: Image > Convert to... > Grayscale (8-bit)
Adobe Photoshop: Image > Mode > Grayscale
Adobe Photoshop Elements: Image > Mode > Grayscale (say OK when asked "Discard Color Information?")
Jasc Paint Shop Pro: Colors > Grey Scale Answered May, 01 2011

you can use ps

Use adobe photoshop... CS2 or CS3 will do... (since lower versions don't support any images higher than the 8bit scale)

Go to Image > Mode then select whatever scale you want to convert it.

read more:answers.yahoo.com/question/index Answered Jul, 25 2011

Go to File>New:
Answered Jun, 22 2011