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In this exercise, I'm going to explain how Cache Levels work inside of Photoshop. I'll also tell you how and why you might want to modify the number of Cache Levels that Photoshop tracks at any given moment in time. Now this topic is somewhat academic. I want to warn you about that in advance, but it's of keen interest to any student of Photoshop and I just have to change the number of Cache Levels to effectively demonstrate how the Auto commands work inside of this Father of our money.psd file. Now notice right off the bat, that I've gone ahead and move this ginormous Histogram panel into the panel dock over here in right-hand side of the screen.
I also saved out a new workspace called Big Histograms. So I still have my original workspace One-on-One which I could switch to at any time but notice if I do, if I switch to One-on-One like so, it doesn't really change things very much and that's because Photoshop is constantly updating the workspaces on the fly and this was the last state of that One-on-One workspace. So it seems as though I have completely messed things up. However, all I have to do is click on this icon once again and choose Reset One-on-One and then it goes back to its familiar appearance without the ginormous Histogram panel and even if I bring up the Histogram panel, it will come up small, which is great because that's the way I created One-on-One in the first place.
Now if I want to switch back to the Big Histogram panel, all I have to do is click on Big Histograms and I created that workspace incidentally by choosing the New Workspace command. All right, so having done that here is a reminder. Every time I switch to a different layer or apply so much as a command to a layer here inside of Photoshop, the Histogram is going to get messed up and it's going to have this little warning, which tells me that it's working from cached data which is to say, it's not entirely accurate, it's taking a lower resolution image into account. I can see that the Cache Level is 3 and unless it's 1, it's not quite accurate.
So the lower the number the better, however 1 means accuracy, and the only way to get a Cache Level of 1 is either click this warning or click on this little Refresh icon right there or you can choose this command from the panels flyout menu Uncached Refresh, either those will do it. Now unfortunately, Uncached Refresh doesn't stick. It would be great if you had a way just to choose a command and every time Photoshop would go ahead and build a Histogram from Cache Level one. However, that's not an option. What is an option is to change the number of Cache Levels and you can do that and here is where things get little bit intricate.
You press Ctrl+K or Command+K on the Mac to bring out the Preferences dialog box and you switch over to Performance right there and notice we have this Cache Levels option. Now when I hover over this area, this History & Cache area that is to say, you'll see a description of everything that's going on in this region, down in the Description field at the bottom of the dialog box. So I can't point to it because I am busying hovering up here but if you look down at the word Description, they are at the bottom of the dialog box. The third line is the beginning of the discussion of Cache Levels.
And it says the Number of cached levels of image data, meaning these are varieties of the image that are stored in memory by Photoshop. It's used to improve the screen redrawn Histogram speed and it makes a big huge difference in that regard. So it does definitely increase the speed at which the Histograms are drawn, that doesn't matter very much to us, but the speed at which the screen is redrawn, it matters a great deal. So decreasing this Cache Levels value can have a negative effect onscreen redraw inside of Photoshop and then it goes on to advice to choose more Cache Levels meaning that you can take this value as high as 8, incidentally.
So you would raise that value for bigger documents with fewer layers and that's the way that this area thinks in general. You'll either have your standard everyday average composition which is of medium size with, let's say 20 or 30 layers inside of it and that's what Photoshop is designed to accommodate by default, or if we raise this Cache Levels value, then it's going to better accommodate big huge photographs for example with just a few layers which might better serve the needs of digital photographers, for example, especially if you're stitching together enormous panoramas.
Then you might want to raise that Cache Levels value. The next sentence says choose fewer Cache Levels that means lower the value for smaller documents with many layers. So you can take this value down as low as 2 is what this little warning recommends. Doesn't like you to go any lower than 2 because then you're really sucking up resources where Photoshop is concerned and the program is going to slow down, but this might better suit your needs if you are a web designer for example, if you're working on small images and you have hundreds of layers inside that image.
This is the better way to go. Then finally, it says changes will take effect the next time you start Photoshop which is indicative of most of the options inside of this panel of the Preferences dialog box. In fact, there is really just one exception History States, you can change a number of History States on the fly without restarting the program. Bear in mind of course, that's just because you take the number of History States from 20 up to 40 and that's 40 per open image, you have to bear that in mind, that's also asking Photoshop to suck up a lot of resources there, but just because you do that it doesn't mean you somehow magically retrieve History State 21 which is fallen off of the list.
Anyway, I am going to leave that value alone. What I am going do is even though Photoshop doesn't recommend it, I am going to take the number of Cache Levels down to 1. I don't recommend you do this either. This is purely for demonstrational purposes, a Cache Level of 1 that is. So if you're teaching Photoshop in a classroom environment, you might have reason to do this, otherwise you don't. Otherwise, if everything seems to be responding just fine in Photoshop, leave Cache Level set to 4, if you're working on big huge images without that many layers, why then take it up perhaps to 6 and then if you are a web designer and you have fairly small images with the hundred or more layers inside of them, then you might take this values low as 2.
Anyway, as I say I am going to lower the Cache Levels to 1. I'm going to click OK and then I'm going to restart the program, and I will go ahead and do that without you and then in the next exercise, I will have restarted and will get down to how the Auto commands work.
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