Join Deke McClelland for an in-depth discussion in this video Cache levels and the Histogram palette, part of Photoshop CS4 One-on-One: Advanced.
- View Offline
The next couple of exercises are devoted to looking under the hood where the three Auto commands are concerned. These guys right here, Auto Tone, Auto Contrast, Auto Color, I'm going to show you exactly what they are doing. So essentially you should be forewarned. We are going to be taking these very simple commands. They are so simple to apply, right? They just do their thing miraculously, mysteriously, magically, and I'm going to make them seem terribly complicated, because behind the scenes they are fairly complicated. The good news is by understanding how these commands work you can better anticipate their behavior, which is really a good thing. And you can start actually taking advantage of them. They are totally under-utilized commands, believe me. If you are in a hurry and you are just trying to get some color manipulations applied across a wide series of images, and you want to get the work done in like five minutes, these are great commands if you know what they do especially Auto Color, by the way, brilliant command.
So I'm going to be to showing you exactly what's going on with them in the next exercise. In this exercise I want to explore this image and I'm going to tell you a little thing about how histograms work and how they are cached in Photoshop. Which we need to know before we can proceed. So I'm working inside of this image called Bling-bling.psd, so-called because it contains a bunch of money. And the term bling-bling I think is a little long in the tooth anymore. Once upon a time sort of a hipster term, now overused. Since speaking of long in the tooth, we have George Washington right here, father of our money, and this is an old school dollar bill. I'm here to tell you the best way to understand how the Auto commands work is with old school American money, just boring old green money. Those greenbacks, they will show you how the Auto commands work. And so that's why I have got this image open.
Now notice inside this file we have a series of layers, a Control layer, and I should say every one of these layers is identical to each other; they are spreading off the same way. But the Control layer is the one we will not change so that you can see what the original scan look like, and then we have Auto Tone and Auto Contrast and Auto Color, and we will be applying those commands to those layers in short order. First though I want you to understand what's going on, where this image is concerned and so we are going to bring up the Histogram palette right there, and you can also get the Histogram palette of course by going to the Window menu and choosing the Histogram command.
And here is what I want you to do, if you are working along with me. I want you to go to the little menu icon right there in the upper right corner of the Histogram palette and I want you to choose the All Channels View so that we can see expanded versions of the histogram, as well as each one of the channels. Now notice the channels are labeled in a very confusing manner at least on the PC here. Red is too far away from the red one. This one, if you were looking at the label you would say, oh, this is the green histogram, this is the blue histogram, and this is the unknown nameless ghost histogram. Don't know what it is, because the labels are in the wrong place.
It'd be really nice if some designer at Adobe, I'm sure they have a couple who will take care of this problem, it's been this way forever. But here is a great way for you to take care of the problem. You just go up to the menu and you choose Show Channels in Color and then you can ignore the labels and you can see this one is red, even though red is a mile away from it, and this one is green and this one is blue, and this one is the Composite view. Now I'm going to switch the Composite view from the RGB to Colors so that we can see the colors overlapping each other. So we can see now blue is just shoved up there and moved into this position. I mean, in other words, we are just taking blue, green, and red, and we are plopping them on top of each other, and where they intersect we get intersecting colors, for example, red and green of course mixed together to form yellow right there.
So this is the best way to work in terms of just understanding what's going on. I'm also going to switch Source to Selected Layer so we are just seeing the selected layer instead of all of the layers mushed together, which doesn't really help us out at all. And then finally I want you to note, I can switch between layers. Notice that I'm switching between layers by clicking on them, nothing mysterious there, but we are not seeing little caution signs, and this guy isn't becoming active. I'm not having a problem with having to update the histogram over-and-over again, and that's because I made a little change to Photoshop's default behavior.
I change, I do not recommend you make. I just want you to know what I have done just in case, for example, you are a teacher, and you want to be able teach this stuff, and you don't want to have to go up there and click this little Update icon every ten seconds, every time you are trying to show off something. This is just an FYI and those of you who are just using the application for everyday use you might want to know about this as well. You go to Edit menu and this would be the Photoshop menu on the Mac. You go down here to Preferences and then you choose Performance, and then you would reduce the Cache Levels to 1 and then you have to restart the program. You have to quit it and then restart it, and then this option takes effect, and this is the way it is for most of the Performance options by the way. Most of them require you to quit the program and then restart it.
And the thing that's going on with Cache Levels by the way, it's normally set to 4 which means that four different versions of the histograms are cached in memory which means that things happen much more quickly, and it's not just the generation of the histograms that happens much more quickly it's switching between channels which if I were right now to switch between channels for you would see it's mind-numbingly slow at 1 Cache Level, it's horrible. So this is why I don't recommend you work this way. And also applying color corrections is a little bit slow; undoing them is mind-bogglingly slow. It takes much more longer to undo them than it does to apply them in the first place. It really munches out the program. So I don't recommend you do it.
When you are just trying to get a sense of what's going on with histograms especially inside the Histogram palette, that does make things better, so that's why I set my number of Cache Levels to 1. If you want the faster performance, but you are going to have to monkey around with updating your histograms more often, you can raise this guy as high I believe as 8, yes, it goes as high as 8, by default it's at 4. And I tell you what, as soon as I'm done with this exercise in the next one, I am going to return it to 4 so that the program behaves itself in the future and I'm going to restart the program. So again, I don't recommend you do what I have done. I just want you to know exactly where I'm coming from. After all, I'm showing you what's going on under the hood. It would be unfair to do something in the background without you knowing about it.
So this is what the Histogram looks like. Just one more thing about this before we move on to the next exercise. I want you to see how these various channels are arranged. Notice that our shadow detail right here, such as it is. We have pretty light shadows. This area here is largely unfulfilled inside of this image. So we have our shadows right about here, and they are fairly neutral, meaning the shadows kind of overlap each other in each one of the channels, whereas our highlights are not neutral at all. We have a lot going on inside green where the highlight detail is concerned, less going on in red and even less going on in blue. That's why we have this greenish-yellowish tinge associated with the highlights inside of our money.
So, that is going to affect how these commands behave, because each one of them is looking at the original histogram and making decisions about how to fix the image based on that histogram. And each one is making different decisions as we'll see. All right, so I set the scene. You know what's going on with Cache Levels, you know what's going on with the Histogram palette, you have it set up properly. In the next exercise we are going to actually apply those commands and see what they do and you will -- I swear to you, you will totally know, you will be an expert on Auto, coming right up.
Recommended prerequisite: Photoshop CS4 One-on-One: Fundamentals.
Download Deke's customized keyboard layouts and color settings for Photoshop under the download feature.
- Using blend modes, adjustment layers, and layer styles
- Organizing a layered composition so it is fluid and editable
- Creating and editing type in Photoshop
- Using blur effectively
- Using adjustment layers to add color
- Combining layers into a clipping mask
- Working with Camera Raw