1. Open your image in Photoshop. In the layers panel, right click on the layer or click the drop-down menu and select Duplicate Layer. This will create two identical layers, one on top of the other.
2.Under the Image menu, choose Adjustments -> Black and White. This menu item will give you a default black & white setting, plus different filters you can use to change the look of your black and white image when you make the conversion from color.
There are other ways of converting the top layer to black and white, but I find the Black and White adjustment to have the most control. You could also desaturate the layer using Image -> Adjustments -> Hue and Saturation and dragging the saturation slider all the way down.
3.Create a rough mask of the part you want to remain in color very quickly with a layer mask. Use the lasso tool or polygonal lasso tool to make a quick selection of the color area. Then go to Select -> Inverse (or Command + I) to select the area opposite the color area. Then, in your layer panel, click the “add layer mask” button. This will create a mask that roughly hides the black and white portion of your image.
Resize and save original, resized and for the web.