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Reducing an image is a pretty simple process. Photoshop simply needs to throw out any extra pixels that it can find to get the image size down to where it needs to be. Enlarging is trickier because Photoshop may need to make up pixels, and that's where you can begin to degrade your image if you're not careful. So we've reduced this image. Let's take it the other direction. I've gone back to my original file, which has the original full pixel count. You can see, I'm currently at 4288 x 2848, for a 17 x 11 inch image, at 240 Pixels/Inch.
If all of this is going by way too fast and you skipped the "Reducing an image" movie, go back and watch that now because it goes into detail about how this Image Size dialog box works. So I'm going to do is go up. Let's say that I wanted to print this image 24 inches wide. Very often, before I do a resizing, I'll play around with the Image Size dialog box, just as a calculator to get a sense of exactly how much I can size an image, what kind of interpolation I'll need to do, and so on and so forth.
I begin that play by unchecking the Resample Image box. I want to see what can happen with just the native pixel count in my image. So for example, I know that I'm going to print at 360 pixels per inch. That means without any interpolation, my image is going to print at almost 12 x 8. But I'm wanting to go to 24 inches wide, so if I dial in 24, that means my Resolution is going to drop to 178. Now, as I mentioned earlier, I need to send the print to the printer at the printer's native resolution, which in the case of my Epson printer is 360.
So I'm going to need to do a lot of interpolation to get from 178 to 360. With experience, you're going to learn how large amounts of interpolation affect your image and whether you like that effect or not. I'm okay at this point with going from 178 to 360. I know that from experience. If I wasn't, I might see that 178 number right now and go ooh, actually I can't take this image that big, maybe I'm going to back off down to, say, 19 inches. That gets me to 225. That's going to be less interpolation upwards.
And so sometimes I'll make some image-size decisions based on that resolution number that I'm seeing. But again, that kind of just comes from experience, and it also comes from your personal taste: how much softening in an image are you willing to put up with, because that's what's going to happen here. We're going to soften image as we enlarge it, and we were possibly going to introduce some artifacts. But I'm going to stay committed to this 24-inch-wide idea. That's going to me a 24 x 15 inch image and without resampling, I am going to be down to 178 pixels per inch.
Just to recap, if I were to send the image to the printer like this, the printer would resample the image up to 360. I don't know that it's going to do as good a job at resampling as Photoshop does, but more importantly, that resampling that it does at that stage could mess up the sharpening that I'm going to apply after I resize. So I want this image at native resolution. That means I need to resample. With the Resample Image checkbox checked, my pixel count is now editable, and so I can go in here and dial in 360.
And I can see up here that I'm doing a whole lot of upscaling. I'm going from a 69.9 million pixel image to 283.7. That's a lot of going up. So my interpolation method is set to Bicubic Automatic. That is going to tell Photoshop to use Bicubic Smoother, which Adobe thinks is best for enlargement. If you're using a version of Photoshop that does not include Bicubic Smoother and Bicubic sharper, that is an older version of Photoshop-- and even some versions of the Creative Suite do not have these options--then you're going to need to go for Bicubic.
When you resample with Bicubic it's best not to do this big a jump all at once. Let me cancel out of this and show you how you're going to do this in steps with a Bicubic resampling. It's best to only go with Bicubic, to only go up in about 10% increments. So what I am going to do is I am going to start my setting my Resolution to 360, which gets my size down to 11 x 7. Now I'm going to check Resample. That locks my resolution into place and now I can start playing with size.
I'm going to switch over to Percent, and I'm going to go up 110%. I'm going to set to Bicubic, say OK, and let it do that interpolation. Now I'm going to go back to Image Size and see what my size is. I'm at 13. Well I need to get up to 24, so I'm going to Percent. I'm going to dial in 110%, and I'm going to keep doing those 10% steps until I get up to the size that I want.
That's one of the great advantages of newer versions of Photoshop is they have these newer interpolation methods that work much better and don't require those intermediate steps that the old Bicubic resampling did. So, let's just put this back where we had it. 24 inches wide, at 360, on Bicubic Automatic. It's going to give me a whole bunch of new data. I am going to let it sit there and think about that. Depending on the speed of your computer, this will take more or less time, and then when it's done I have this. Now I'm currently looking at 30%. I am going to zoom in some.
Now, I'm not going to do too much fretting over what I see here at 100%. The image is definitely softer, but what I'm looking for are these kinds of things. These stair-stepping patterns that came in here, that's the result of the interpolation. You may look at them here and go, oh my gosh that looks terrible, but remember, we are looking at individual pixels right now. Remember, too, that when this is printed 24 inches wide you're going to stand back from it. I'm even standing back from my monitor right now and those artifacts don't look so bad.
But that's the kind of thing you can end up with from really severe upsampling. The other thing that's happening is that this bit of dark edge that's come around the finger here is being exaggerated a little bit. But overall, I'd say this resizing went very, very well. The only way to find out for sure if my sharpness and my artifacting is acceptable is to do a print and check it out. This image will still need some sharpening, and we'll cover that in the next chapter.
Just remember that when you're scaling up you need to pay attention to resolution just as you always would when you're scaling down. Try to assess how much scaling you are doing and for your first large prints, pay attention to that degree of scaling so you can learn to develop a sense for how much scaling you can get away with. And remember, it's Bicubic Automatic or Bicubic Smoother if you have those choices; if not, then it's Bicubic in 10% increments.
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