Learn how to use the 16 Bit per Channel Space in this Adobe Photoshop CS2 Advanced training video.
Tags:16 bit,adobe,adobe photoshop,adobe photoshop cs2,channel space,macromedia,total training
Grab video code:
Now in this first lesson, we are going to take a look at the Levels command. But we are going to take a very advanced look at the Levels command inside Photoshop. Now the remarkable thing about the Levels command is it's one of the earliest commands ever introduced to the program. It actually shipped with Photoshop 1.0 and it has changed a little bit over the time.
But the amazing thing is it hasn't changed very much and it remains one of the most powerful correction features inside the software. Just in case you are not familiar with the command, I am sure you are, but just so that we are all on the same page here, the Levels command is basically the big brightness and contrast adjustment command inside Photoshop, allows you to adjust the brightness of highlights, the darkness of shadows and the brightness of the mid tones in between.
Go up to the Image menu, choose Adjustments and there it is, it's the Levels command under the Adjustments sub-menu here and it has a keyboard shortcut as well, Command+L on the Mac or Ctrl+L on the PC.
Now if I just start in applying the Levels command, I am going to apply what's called a destructive modification to the image, meaning that I am going to permanently, and I say permanently inside of quote fingers here because nothing is really permanent inside of Photoshop until you save the image.
But you are applying a permanent change to the pixels inside the image, to the colors inside the image. That is to say, the only way to reverse the effects of the Levels command, when applied as a flat command, is to either undo the modification or back step through several layers of modifications and that's no fun.
So it's nice if you can find a non-destructive way in order to apply the edit and there are two ways to apply modifications non-destructively, to apply the Levels command in particular without destroying, without permanently modifying the colors or pixels inside the image.
One way is to go to the Layer menu, choose New Adjustment Layer and then choose Levels. The problem here is, you create a new layer inside the document and that can be a good or bad thing but if you want to still save your image to the same file format, then you might not want to go this way. By default this Levels command does not have a keyboard shortcut assigned to it. You can always change that if you want to but by default it's set up this way.
Another way to work, to go ahead and apply a flat change to an image, particularly if you are talking about a photograph like this one, where you don't want to create a bunch of layers, you have no desire to create a special effect, you just want to improve the colors inside the image, is to before you apply the Levels command, to go up to the Mode sub-menu under the Image menu.
So go to image, choose Mode and then choose this command right here, 16 Bits/Channel, or you can take advantage of my keyboard shortcut Shift+F4 and you will only see this keyboard shortcut if you went ahead and loaded my Deke Keys CS2 Advanced keyboard shortcuts as directed in the prologue to this series.
Those allow you to convert between 256 brightness values per channel inside the image, to as many as 65,000 brightness levels per channel inside of an image and it turns out, just so that you know those of you who are interested in such information, this actually switches the image to effectively 15 bits of data per channel. It really gives you 32,000 brightness variations inside of an image and one of the bits is held back, just so you know.
Let's get sort of a practical sense of why this approach is important inside of an image. I want you to go ahead and open up this image here. The bride.jpg, it's inside the Lesson 1 folder, which is inside the project files PSCS2 Advanced folder that you installed on your hard drive.
This image comes to us from Alexandra Alexis via istockphoto.com. Beautiful image of a bride in a strapless dress. What I want to do is I want to expand the contrast inside this image, boost the contrast a little, balance the brightness value a little as well. And I am going to do that as non-destructively as possible, where a flat image is concerned, by applying this change to a 16 Bit/Channel version of the image.
So, let me sort of point you here toward the Titlebar. Notice that it says RGB/8. That means we have 8 bits of data per channel and as many of you know, in order to figure out exactly how many brightness variations you have, you take 2, which is a bit, 1 bit of data, 0 or 1, so you have two different variations there, to the 8th power in order to figure out that you have 256 different brightness variations per channel inside the image. This is an RGB image, which means that we have three channels of data, therefore this is a 24 bit full color image.
I am going to go now up to the Image menu, choose Mode and choose 16 Bits/Channel. Now you will not see any change to the image. The image will look the way it always looked. The only difference is the Titlebar is now showing us RGB/16. So we have 16 bits of data per channel inside this image. I was telling you that one of those bits of data is held back. So it's really 15 bits of data and so far as our practical ability to edit this image is concerned, that means 2 to the 15th power, which is about 32,000 little more variations, 32 brightness variations per channel and you take that times 3 because this is an RGB image. You get into trillions of potential colors, trillions of potential colors inside this image.
Now this image doesn't even contain 16 million pixels. So it wasn't even taking full advantage of the 8 Bit/Channel space, and now we have thrown it into a much larger space, which means Photoshop is spending more time editing the image. It's a lot more processing. It's going to take up more room on disk and we are not going to be able to save it to the JPEG format, I am going to have to save it to the TIFF format or PSD or something along those lines. So why in the world should I do it? I can't take advantage of all these trillions of colors. So why should I go into this 16 Bit/Channel space in the first place?
Well, let me answer that question first. Why go into this 16 Bit/Channel space? The reason is, you have a lot more wiggle room. You can make all sorts of edits, you can apply the Levels command multiple times in a row under certain conditions, which I will tell you about in just a moment, without destroying the image, without harming the colors inside the image.