This is a rather simple tutorial that can turn any coloured image into a black and white image with a strip of highlighted colour. It doesn't take long to complete and you will wonder why you haven't thought of this before. For this tutorial you will need Photoshop (or similar) and a colour image with a highlighted area.
Step 1) The basic idea behind this technique is to use the history brush to reverse the black and white state that we will apply. Depending on you settings you will need to change the history states within the preferences. Open up the preferences menu Cmd/Ctrl + K and selection the performance tab.
On the right you should see history states. Depending you your skill with the mouse you will need to change the amount of states. I recommend 20-40. To many and your memory will be filled up very quickly. To little and you will run into the chance of running out of states.
Step 2) Load up the History Palette. This can be accessed from Window > History.
Step 3) Load your image. I'm using a train i've found on Wikipedia. Ideally I wanted to use a image of a person in a busy street standing on there own. I couldn't find one so you are going to have to stick with a train instead. Click the image below for the full sized version.
Step 4) Go to Image > Adjustments > Black and White. You can fiddle around with the values but I just press ok. This will turn your image black and white.
Step 5) This is where the history brush comes in. Using the history palette select the original image from the left hand side. As shown below.
Step 6) Then using the history brush from the palette (Y) brush over the areas you want to be re-coloured. If you go out of the lines it doesn't matter. This is resolved in the next step. Make sure the mode is set to normal.
Step 7) If you have gone over the areas you want to stay black and white it is very easy to correct. All you have to do is change where the history brush is being used from. At the moment it is taking the data from the original image. But if you set the little icon to the Black and White option has appeared you colour over black and white back into the image. Really simple.
Step 8) Save out your image and you are done. I have included some extras examples. Click the images for the full sizes.
Its a really simple and cool effect. I like it. Post your links to your image and lets see what you have come up with.