In Photoshop what is the best way to turn a colored picture into a Black and white one ?

Image>Mode>Grayscale

The best, easiest and fastest way is desaturating.

From the Image menu and in Adjestment you will find desaturate and the shortcut for this is "Shift+Ctrl+U.

Convert COLOR MODE to GRAYSCALE

 Go to Image - Mode - Grayscale

3 Quick Ways to Go Black-and-White

There are a couple of simple ways to get black-and-white digital photos.

1. Use your camera’s built-in B&W setting.
2. Convert to B&W using the pre-set filters in iPhoto/Picasa/Photoshop Elements.
3. Use Photoshop (or GIMP or whatever) to desaturate or change to grayscale.

These methods all work, but you end up with flat, muddy photos. Bumping up the contrast will improve matters, but to get a black-and-white picture that really pops, you’ll have to go a little deeper.

Do It Your Way

Keep in mind is that there is no God-given Right or Wrong in photography. The main thing is getting your photo to look the way you want.

Do you want to match the feel of the color version? OK. Make it dark and brooding? Sure. Crazy-high contrast and surreal color values? Fine, go nuts. It’s up to you.

Now, how do you get there? Start with the RGB channels.

Introducing RGB Channels!

Any RGB image (i.e. color) can be divided into three channels. If you open the Channels palette (Window -> Channels) you will see four channels for any color image: RGB, Red, Green and Blue.

The channels represent the proportion of each color that makes up the entire color image. Each color appears lighter in its namesake channel (i.e. red-colored objects look paler in the Red channel) so the three channels will look very different.

• The Red channel generally shows pale skin tones and dark skies.
• The Green channel has a good mix of tones and tends to look closest to the original color version.
• The Blue channel features very pale skies and dark foliage.

Turning a Channel Into Back-and-White

If the look of a certain channel takes your fancy, you can convert that channel to a black-and-white image.

With the channel selected, go to Image -> Mode and select Grayscale. Discard the color information when prompted, and layers if applicable.

Now you have a lovely black-and-white photo!

Use Auto Levels, Levels or Curves to get crisp whites, deep blacks, and a level of brightness that you like, and you’re done!

Next Up… The Channel Mixer!

What if you like the general look of a particular channel, but want to fine-tune your results? Use the Channel Mixer instead.

The Channel Mixer allows you to determine how much of each channel is expressed in the final image, using sliders for the Red, Green and Blue channels.

How the Channel Mixer Works

Say you want to darken a red object to make it stand out, but you also want to keep the sky from going too dark?

You’d subtract Red to darken the red object and add Blue to lighten the sky. Low values of a channel darken its namesake color, and high values lighten it.

With the right mix of channels you could make a color completely disappear. Not that you’d want to, but you could.

Working the Percentages

The channel percentages should theoretically add up to100% (i.e.50% Red +40% Green +10% Blue =100%). More than100% means lighter images and less than100% means darker images, so it’s really up to you. You can also use the “Constant” slider to adjust overall brightness.

The default option is100% Red,0% Green,0% Blue, but 30% Red,60% Green,10% Blue is a good starting point.

Using the Channel Mixer

The easiest way to use the channel mixer is to create a new adjustment layer. Go to Layer -> New Adjustment Layer and select Channel Mixer.

Check the “Monochrome” box, then click and drag each slider to see the results.

Move the sliders until you’ve got the look you want, then click OK. If you need to tweak it more later, double-click on the slider icon on the adjustment layer to re-open the channel mixer.

Now to fine-tune the contrast. Auto Levels gives you decent results, or you can add a Levels adjustment layer (Layer -> New Adjustment Layer -> Levels) and do it yourself.

Bump up the contrast a little, adjust the brightness, and you’ll be in great shape!