Creating good Black and White images from a color image is a very complex task, there are many many ways to do it in Photoshop alone. I will demonstrate one simple one here that uses a Gradient Map adjustment layer.
This is a very simple technique that is easy to put into an action, start off by opening your color image and make sure your layer window is showing using Window->Layers.
Create a new Gradient Map adjustment layer using Layer->New Adjustment Layer...->Gradient Map... or using the icon on the layers window.
Immediately after creating the Gradient Map layer you will see a window like the one above, this will contain a gradient using your current selected colors, I had black and white selected already. Click on this strip to see the full options window. In the Presets frame choose the 3rd square this will give you a good Black and White.
Once this is done you can change the Smoothness to your liking, some people like 33%, but it really depends from image to image and your personal taste.
Once you are happy with your results choose Ok on both dialogs and you will have a Black and White image as result.
Amusement Park - Brighton, UK
I was using two Hue and saturation adjustment layers for changing colour to black and white for some time, and just for the sake of experiment I added a gradient map layer, I was amazed at the control and I use this method all the time without the hue and saturation, I just want you to know that in all my years using Photoshop(home user)you are the first person who has ever mentioned it, I think it is the best method.
I have learn't to create black and white images that i love, it took some time, but I think using this method is fabulous, and I will be using it in future to see what results i can get! Thankyou
I haven't seen this method of black and white-ifying, so thankyou! This is great! Soo many possibilities, heh!
Mike
I came by this method by change in Photoshop, it works better dan de Channel Mixer in my eyes...and I use it all the time
still I am wondering what the hell is does...because it goes from black to white, but in your new picture you do not see a thing of that 'line'