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The previous movie was a bit academic, which is why I want to show you how these interpolation settings affect an actual continuous tone photograph and offer you some advice for how to use them. So what I did was take this high-res panorama and then once again choose the Image Size command, make sure Resample Image was turned on, set the Resolution value to 100 Pixels/Inch, just as I did when downsampling this image for email, and then I tried out each and everyone of the manual interpolation settings. And let me show you what that looks like.
I'll switch to this file called Interpolated panos.psd. Notice that we're seeing the image at the 100% view size. I'm going to zoom in quite a bit here because we'll need to see these pixels in detail. Now once again this file has layer comps inside of it. This first slide shows the result of downsampling the image using the Nearest Neighbor setting, which just drops pixels, and as a result we end up getting this pretty choppy detail. One might argue that the detail is very crisp and we don't have any halos around this mountainous formation here, however, we have jagged transitions.
This next slide shows up Bilinear Interpolation, and notice that the Bilinear setting ends up generating the smoothest detail of them all, however, we end up with some almost plastic-looking forms. Next is Bicubic Interpolation. We get more detail, it looks less plasticky, but we're starting to see some halos around the sides, especially here in the sky. It's subtle but it's there. If we want to get rid of those halos, then we would switch forward to the next one. Very subtle distinction by the way, you'll have to look closely at this.
But what we're seeing now is Bicubic Smoother. If we want sharper, crisper details, we'll go ahead and switch forward to Bicubic Sharper which ends up generating the most halos of them all. So this is a pretty big difference. Again, I'll show you Bicubic Smoother and then this is Bicubic Sharper. Now just to eliminate any confusion, I want you to see what these settings are called inside the Image Size dialog box. So I'll call up the Image Size command again and notice right here, each one of the three Bicubic settings includes a parenthetical after it.
So standard Bicubic Interpolation says best for smooth gradients. Well, that's not really true. It's not that many times when you're concerned about downsampling gradients, rather it's that standard Bicubic setting that goes ahead and preserves the details with a little bit of haloing and it tends, in my experience, to work best when you're downsampling for print, and I'll explain why that is in just a moment. Bicubic Smoother says best for enlargement, which is why it's selected by Bicubic Automatic when you upsample an image. However, it's also useful if you have noise in the image, that is, digital grain inside the sky region, for example, or if you want to take it easy on portrait shots.
After all, you don't necessarily want to sharpen the pores in a person's face. And then next we have Bicubic Sharper, which says best for reduction, which is why it's selected by Bicubic Automatic when you downsample an image. And it tends to work great if you have a low noise file and you're downsampling it for the screen, whether than means email, or the web, or what-have you. All right, so I'm going to go ahead and Cancel out of this dialog and I'm going to zoom back out here and bring up some more slides. These are my rules specifically for downsampling by the way.
When in doubt, especially when you're downsampling for the screen, you can stick with Bicubic Automatic which applies a Bicubic Sharper setting. However, if you plan on sharpening the image, which typically happens when you're preparing the image for print, and here's what that looks like. Immediately after downsampling the image you would go up to the Filter menu, choose Sharpen and then chose either Smart Sharpen or Unsharp Mask depending largely on taste, and I'll be explaining in all kinds of detail how those filters work in a future course.
But the thing about sharpening is that it adds more halos. And the last thing you want to do is take those halos that are automatically generated by Bicubic Sharper and then exaggerate them using a Sharpening filter. So again, if sharpening, use Bicubic (best for smooth gradients), and then finally, if the image is noisy, if it contains random pixel variations, then try Bicubic Smoother instead. For continuous tone photographs you can safely ignore Nearest Neighbor, and Bilinear is a kind of middling function that doesn't serve a lot of purpose.
So there is my advice for employing the interpolation settings when downsampling a photographic image here inside Photoshop.
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