“Please Stick To One Channel and Watch That”

OK first just to clear things up this is not a post about television hoppers, this is post about Photography. Secondly and more importantly your photos have channels.

Depending on the image mode of your photograph you will have different numbers of channels. An images colour elements in Photoshop or another image editing software are split into channels. If you have an image that is an RGB image, it will be split into three channels Red, Green and Blue. The Channels palette will represent this as three separate channel layers. If you think about traditional printing, each channel is a plate with just one colour but when mixed with the other two creates the full colour image.

There are several image modes; CMYK (Cyan, Magenta, Yellow and Black), Greyscale (a scale from light grey to dark sometimes called black and white) Lab (this has three channels lightness which contains all luminance information and an A and B channel which contains colour information.) There are more but at the beginning we will start with those.

For most users of Photoshop this is about as far as their knowledge on channels goes. Channels can be useful for many other things than just giving having the colour information stored; they can be used for creating black and white images to saving selections.

I select you.

Photoshop has a neat section mode called quick mask.  Using the quick mask mode you can use the paint brush to paint the area of the image that you want selected. When you exit the mode the area is selected. When you do this your Channels palette will gain an extra channel temporarily while you are in the quick mask mode. When you exit the mode the channel will disappear

You can also save the selection you have made in doing tis it will save the selection to your channels in a new channel. This is useful if it is an area in the image that you are going to the reselect saves time in manually reselecting the are time and time again, especially if it is a complex selection. When you save your section a new channel will appear called an alpha channel. This channel does not affect the colour of your image directly. Alpha channels are masks that can be edited to manipulate your section.

Where the filters go

Applying filters to separate layers is quite common in Photoshop but you can also apply filters to channels. By apply filters to channels you can create a more stylised image. A good example would be to apply a Gaussian blur to an Alpha channel that you have made from a section. This will soften hard edges and can be used to help blend differ components of an image together. Just like layers, channels can be duplicated to preserve the original channel.

Another simple idea would be to turn off a colour channel to remove one colour to create interesting colour effects. If you like the image with the channel turned off, remember to delete the layer because if you don’t when you open the image again it will turn back on.

As you can see from the image above i have turned off the black channel.

Should we split up?

You can do two great things with channels, one is to split them up and other is to merge. If you split the channels you will create a new greyscale image for each channel. For example if you had an RGB image you would have 3 greyscale images. This is a neat way to create black and white images. I will be posting later about how to create black and white images using channels.

The merge option will reunite the split channels back together in a single document. In fact this option will merge any number of greyscale images as long as they have the same dimensions. This means that you can create an image where each channel contains a different Image. This is a great are to play with and see what you make.

The Math

Layer masks have made working in channels less common now when making masks and creating selections. Alpha channels do have an advantage over layer masks. With an Alpha channel you can blend several channels together to create new ones. Mixing channels is nothing new. The Calculation command in the image menu has been part of Photoshop since the beginning but few users are aware of how creative it can be.

The calculation command allows you to build up several masks that you can then use for subtle colour correction. For example, if an area of an image  high in contrast or saturation.

To use the calculation command you need to have at least one document open with more than one layer with different contents. Select the calculations command form the image menu and experiment with the different options. You can choose two different sources from the list of open documents as well as specific layers and channels from each source to be blended.

Calculations have two extra blending modes; Add and Subtract. These can create extra effects of offsetting and scaling. A live preview shows the results of the blended channels, which can be saved as a new channel.

You could build entire illustrations from just using calculations.

Wowzer brain overload

As with a lot of things channels can be overwhelming at first but playing around with them is the best way to learn. Photoshop is a huge sword that can be wielded with great ease by just having fun and experimenting which, is one of the best ways to learn (as long as you remembered what you did.)

For channels here are some bullet points to remember.

  • Each channel represents a colour like a printing press with just one channel being one colour but when all are mixed it creates a colour image.
  • When you save a selection it is saved in the Channels palette as an Alpha channel.
  • Alpha channels do not directly affect the colour of an image but can be used to creat localized colour correction and blending.
  • You can have up to 52 channels in one image.
  • Filters can be applied to channels
  • You can remove colour channels to create different colour effects.
  • In splitting the channels you can create a black and white image
  • In merging the channels back you can create a new composite image.
  • You can use the calculations command to blend channels and layers together.

This really is just the beginning of channels and there is so much more you can do but I am really looking at the basic beginnings for photographers.

I hope you enjoyed the post.

Let me know what you think or any questions you may have.

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6 thoughts on ““Please Stick To One Channel and Watch That”

  1. Yup, my brain is frying ever so gently but even just playing with the split channels was interesting. In one instance It effectively gave me a desired effect just reducing it to the single (red) channel. The background became less intrusive, the principal subject popped more and it was very straightforward. On the other hand blending 3 channels I had adjusted individually gave a slightly odd colour cast to the image so it clearly needs some experimentation. I am a sucker for B&W and generally use Silver Efex Pro v2 so I am looking forward to your session on creating B&W images.

    • Writing the post made my brain fry trying to make channels digestible.

      Splitting of the images for black and white can be a great conversion method. I am posting my black and white videos on Mondays.

      Thanks for your comment.

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