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In this exercise, we are going to down sample for a different occasion. The idea is that we want to be able to email the image so that it looks great on another person's machine. So I've got a few sample files open here. The first one is called Shepherd (360- down), meaning 360 PPI and we down-sampled it from the high resolution original, so it looks great right ready for print, whereas of course the next guy Shepherd ( 360-up) that we up sampled from the low resolution version of the image, looks terrible.
So you just have those two versions of the image to compare if you want. But now we are going to transition from line art which is actually great for demonstrating how upsampling and downsampling works, however, you're probably going to be doing most of your work in Photoshop on continuous tone photographs. So I've got one for you. It's called Moab skyline.jpg and it comes to us from Miroslav of the Fotolia image library about which you can learn more at www.fotolia.com/deke. And this is a huge image. I am going to go up to the Image menu and choose the Image Size command or press Ctrl+Alt+I, Command+Option+I on the Mac.
And you can see that it's 7000 pixels wide, 2822 pixels tall and that's a total of 19,754,000 pixels, which means that it was probably shot as a series of photographs and then stitched together using Photoshop's Photo Merge command which is a great way to create panoramic shots like this. In print it's going to be 17.5 inches wide and 7 inches tall and it's going to have a Resolution of 400 pixels/inch, we could of course change that if we wanted to, without changing the pixel count.
But let's say what we to do is we want to prepare this image for another persons screen. So I would make sure Resample Image is turned on, Constrain Proportions should be turned on as well, unless you want to squish the image and Scale Styles, good idea to turn it on although it doesn't matter for a flat image like this one. Now I am going to change this Resolution value to 100. Why 100? Well, it's kind of random, I have to say. I'm not trying to match the resolution of the other person's screen. I could enter 72 like everybody thinks you are supposed to do when you're going to the web but that doesn't really have any bearing on reality.
It's up to you if you want to go that route but it's not necessary. I'm just entering 100 in general because I'm trying to get that image size down to a hundred times that in pixels which is going to be 1750 pixels and I can see that the Image Size is dropping from 56.5 megabytes down to 3.53 megabytes. So we're reducing the image and it's going to be small enough in order to email. If I save this out as a JPEG file and I've tried this, the JPEG file even at the highest quality setting, so great quality ends up being about one megabyte which is a perfect size at which to email a big glorious image like this one here.
And it's still going to be big enough so that whoever looks at the image can zoom it if they want to. All right, so the big question becomes which of the interpolation methods do I use, Nearest Neighbor and Bilinear are right out, you'd never use Nearest Neighbor for a continuous tone photograph and you just never use Bilinear at all. So it's going to be one of the Bicubic options. Bicubic for smooth gradients, it's going to preserve the transitions, Bicubic Smoother, is going to try to smooth away the noise and Bicubic Sharper is going to add a little bit of sharpening which is ideal for screen purposes.
And this is going to the screen after all, so Bicubic Sharper is probably the best way to go. However, I've created three sample files that show off each one of these Interpolation methods. So I am going to cancel out and we are going to switch from this image here, Moab skyline.jpg which we are viewing at the 25% zoom ratio by the way, we are going to switch to Bicubic (default) which has been downsampled just like I showed you to 100 pixels/inch using the default Bicubic Interpolation setting. We're seeing the image at the 100% zoom size, so it's going to look great.
So if you are working along with me and I say this because I am not sure you can see this in the video or not, but here is the original image at 25%. It might look a little softer or a little gummier on screen and that's because Photoshop is interpolating the image on the fly. In order to scale it down to the 25% zoom ratio it has to perform real-time interpolation in cooperation with your OpenGL video card. Whereas, when you're looking at Bicubic (default), which should look ever so slightly sharper at 100%.
No on-the-fly interpolation is happening, so the pixels you are seeing are the pixels that are actually there. Anyway, that's Bicubic (default). Now let's move on and this going to be really subtle. You are going to have to keep a very close eye on the face of this cliff right here and the edges as well next to the sky. Here is the Bicubic Smoother.tif image and that is a function of course of the Bicubic Smoother Interpolation setting and it does smooth out the details just ever so slightly. So again, it's really designed to get rid of noise that's about all it supposed to do.
Then finally we have Bicubic Sharper.tif this one right here, and if you look it closely there you should be able to see a difference between here is Bicubic Smoother, see the lines on that cliff and the edges as well. And here is Bicubic Sharper, it is a more sharply detailed image that's for sure. But only so slightly that you are going to see that at the 100% zoom level on screen. No way, this sharpness is going to survive in print. So if you're really thinking about sharpening an image and sharpness is great, right especially with this kind of image, with the landscape image.
We're trying to call attention to all those wonderful earthy detail. Might not want to sharpen a person's face. It depends a portrait shot, because you might be bringing out bad detail. And you'll learn more when we discuss the sharpening filters later in this series. Let me show you another way to sharpen. I am going to switch back to Bicubic (default).tif which is the default unfiltered interpolation setting. And now I am going to go up to the Filter menu, choose Sharpen and choose Sharpen. Now this isn't the command I normally use, I typically recommend people use Smart Sharpen or Unsharp Mask, however they're much more complicated, and for our purposes right now we are going to stick with the Sharpen filter.
But watch what it does. It does a great job of sharpening that image for screen work and it actually renders out a slightly more sharp version of the image than Bicubic Sharper.tif. So if you want a little bit of sharpness as you are downsampling then go with Bicubic Sharper. If you want a little bit more, then you'd go with Bicubic (default) and then you'd apply that Sharpen Filter right there under the Sharpen sub-menu. And I hasten to add. You wouldn't want to apply Sharpen to an image that you down-sampled using Bicubic Sharper, okay, so this is only for Bicubic default.
All right, and then finally what you do is you would go to the File menu. You choose the Save As command because you don't want to save over your original, anytime you resample an image, you want to follow-up by choosing Save As. I'll go ahead and rename this image Downsampled Moab or something along those lines, like so and then I will choose the JPEG file format, because JPEG is going to be your best bet when you trying to email an image to somebody else. It's a widely compatible file format. And then click on the Save button and up will come the JPEG Options dialog box.
I recommend that you choose the highest Quality setting which is 12 maximum, and then switch to Baseline Optimized for the smallest possible file, and then click the OK button in order to save that image and you are done. So that is how you downsample an image if you want to send it off for display on another person's machine.
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