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Black and White Selective Desaturation

Sepia Selective Desaturation

I am going to use Photoshop for this quick tutorial, but it should be a pretty similar process for other programs.

The first thing I should say is that this technique will only work well for certain photos. As we will be removing a whole colour from the photo, the colour should be present in one area only, so that you don't get areas of black and white scattered around your image.

Here is an example of the type of photo that doesn't work very well:

There are a lot of colours in the photo, and some are not actually as they appear. For example, the grass is not green, it is actually under the yellow channel. The faces are also under the yellow channel, not the red, as you may or may not expect. You'll learn more about why this is important later.

Now we have a bad example to work with, let's see what we want to desaturate. I think I'm going to try and desaturate the middle costume, the one in the red top.

Without worrying about how I did this yet, I'll show you that under DPC's basic editing rules, it's impossible to only desaturate that one guy:

I've desaturated the red for his shirt, and the blue for his shorts. As you can clearly see, the crowd have also had their clothing desaturated, and the blue matt has lost its colour too. You'll notice that even now, there is colour left on the guy where we don't want there to be any colour. The legs are still looking pink, and the head is yellow. Once we've desaturated these 2 colours we end up with an even worse looking picture.

It looks like we've just desaturated "because we can". It's completely random and has no useful purpose. This is never a good idea in photography. You should only ever do something if you feel it will benefit the photo, not just because you read a tutorial and wanted to try it out.

Now that we know when not to use selective desaturation, let's learn how to use it in an effective way.

For basic editing challenges, you often have to have the idea that you want to selectively desaturate when you take the photo, so that you can make sure that the colour you want to desaturate isn't present in other areas of the photo. It is also very important to have you white balance set correctly, because having it wrong could create a slight colour cast in the photo, causing your selective desaturation to desaturate other things which you want to remain in colour!

For an example, I will use this photo of mine, which I took with the idea of desaturating later on:

I cut the word 'Green' out of transparent red film, so that anything behind it would become red. I could then desaturate the red layer to leave a field of green grass, with the word green in black and white.

Okay, so how do you selectively desaturate? First of all go into hue/saturation.

The following window will appear with a number of settings:

Hue shifts the colours of the whole photo.

Saturation changes the strength of the colour.

And lightness, well, isn't it obvious?

At the top of the window, it says Master. This means that your adjustments are currently effecting all of the colour channels. Click that, and you'll see a list of different channels. In this case, we want to desaturate red, so select the red channel.

You can then move the saturation slider all the way down to -100 to make the red channel black and white.

But in this example there is a problem. Some of the grass has reflected onto the red film and that means certain areas aren't desaturated. In this case it is easy to fix. The areas that aren't desaturated look yellow, so lets see what happens when we desaturate the yellow channel. In theory everything should be fine.

That's weird. Even though the grass definatly looked green, it was under the yellow channel. Since it looked very green to our eyes, it was most probably right on the boundary between yellow and green. Around the letter 'G' there is some area of green, so this confirms the fact. The yellow on the G which we wanted to desaturate was much more yellow, so this means we can shift the hue and fix the problem. Here is what we do:

First, set the saturation of the yellow channel back up to 0 so we can see colour again. Next, we want to shift the yellow channel over toward the green, so we change the hue slider. As you can see from my example, +35 has made the grass a definate green, not yellow. However, as the yellow on the lettering was further towards the middle of the yellow channel, it still remains within it, so we have separated the 2 areas into 2 different channels. This means that we can adjust them both separately now.

It is important that you press 'OK' at this point, confirming any changes you've made. This will set all the sliders back to 0 and enable us to work on the new image, rather than just adjusting the settings we made on the original. Once you've pressed OK, go back into the Hue/Saturation setting again. Then go back to the yellow channel, and try desaturating now.

Looking much better now! One problem remains though. The grass is looking un-naturally green. To fix this, just press OK to save the changes so far, then go back into Hue/Saturation, and select the green channel. If you do -35 for hue (because we did +35 before), the grass should go back to its original colour, and we've got rid of the yellow on the lettering already, so it won't be effected.

And that's the selective desaturation done! This was quite a complicated example, but you should definatly know how to do the basics now, and also how to try and correct it if it doesn't work out exactly to plan.

In my challenge version of this photo, the lettering appears much lighter. That's simple to do too. When you're desaturating the red channel, play around with the lightness of the red channel too.

Sepia Selective Desaturation

The steps are similar, but instead of desaturating the relevant channels all the way, just desaturate them part of the way. This dulls down the colours a bit. Then, adjust the hue until the channel is the tone of sepia that you want it to appear. You don't have to make it sepia. You can make it blue, green, pink, whatever fits your photo the best. In the photo above, I decided that a red sepia looked best. It really improves the mood over the normal green colouring of the trees.

I hope this quick tutorial helps you, and that you now know how to do selective desaturation without any trouble. If you have any questions or anything, feel free to either PM me, or ask in the forums for help.

-Ben

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