One of the simplest ways to turn a color image is to Black and White is to press CTRL+SHIFT+U. But you have no control over it. There is a much better way by using Camera Raw. You must know how to open an image in Camera Raw. Do not worry if you do not know how to do it I will show you how.
A color image turned to Black and White with Camera Raw.
Step 1 : After opening Photoshop go to File>Browse in Mini Bridge.
Step 2 : In Mini Bridge navigate to where your images are and right click to image to open it in Camera Raw.
The image opens in Camera Raw. You will find this image here
It belongs to eDamak
Step 3 : Click the icon shown and click on Grayscale Mix.
Step 4 : The image turns Black and White.
Step 5 : Place the cursor on the image. You can see what it looks like instead of the usual arrow.
Step 6 : Drag the cursor to the right or left. The cursor changes to a small two-headed arrow.
Step 7 : As you drag the cursor over different parts of the image, the portions become light or dark.
Step 8 : I am moving the cursor on the sky. I am dragging the cursor to the left. It darkens the Blues in the sky, even though this seems to be a Black and White image.
Step 9 : See the controls at the right. There are 8 of them. The Aquas, Blues and Purples in the sky move of their own accord.
Step 10 : I am making the wooden planks darker by moving the slider to the left. If you move it to the right it will brighten the colors.
Step 11 : Once you are finished, click the Open Image to open it in Photoshop.
The Black and White image opens in Photoshop. That is all. You can see how easy it is to do it and what good results you get.
Now what do you do to get the image back in Color?
Step 12 : Close the image first. Open again in Camera Raw. Click the icon at the top and click on Parametric Curve, Hue, Saturation and Luminance one by one.
The Color of the image is restored.
Step 13 : Open the image.
The original image opens. To save it click on File>Save as.
Step 14 : Save as Jpeg.
Other Photoshop tutorials are here
