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Get the ultimate foundation in Adobe Photoshop CC, in this update to the flagship series Photoshop One-on-One. Deke takes you on a personalized tour of the basic tools and techniques that lie behind great images and graphic design, while keeping you up to speed with the newest features offered with Creative Cloud. Learn to open images from multiple sources, get around the panels and menus, and work with layers—the feature that allows you to perform masking, combine effects, and perform other edits nondestructively. Then Deke shows how to perform important editing tasks, such as cropping and straightening images, adjusting the luminance of your image, correcting color imbalances and enhancing color creatively, and finally, retouching and healing.
This next topic is pretty technical, but I think it's important to understand if you really want to come to terms with the Image Size command here inside Photoshop. It's all about methods of interpolation, which is how Photoshop takes the existing pixels inside of an image and decides to rewrite them when either upsampling or downsampling. And to give you an idea of what I'm talking about, I'll go up to the Image menu and choose the Image Size command. Whenever the Resample check box is turned on, you have access to this pop-up menu, and these are the interpolation options, right here. By default, it's set to automatic, but you can overwrite that default setting by applying any of these other 6 options.
And let me show you how those work. I'll go ahead and press the escape key in order to exit the dialogue box, and I'll switch over to this image, here. So, I took these gray checkers, which we're viewing at the 200% view size. And then I downsampled them to 72% using each one of the interpolation settings, and I came up with this diagram here. And then after I downsampled them, by the way, I went ahead and magnified them to 800% so we can really see what's going on.
Alright, so I'll go ahead and zoom into this first guy right here, nearest neighbor, and nearest neighbor applies no interpolation whatsoever. So it does't average the pixels in any way. It's just one color ends up winning or losing and that's all there is to it. So as a result, we have some rows and columns that are very thick like so, and others that are thinner, like this one here. So there's a certain unevenness going on. I never use nearest neighbor for down sampling, by the way, but it can be useful for upsampling.
For example, that's how I up sampled each one of these interpolative results so I didn't introduce any transitional pixels. And as long as you interpolate by even numbers, that is multiples of 100, then you'll increase the size of the pixels uniformly. The next option here is bilinear, and it is the simplest of the actual interpolation methods, because it really just runs a straight average of the pixels. So in this case, this area became sort of a middling grey because Photoshop was trying to average between the dark gray and the light gray.
Next, we've got the various Bicubics and what Bicubic tries to do is increase the sharpness, uses a series of derivatives that you don't need to know about. It's much more complicated, but it's trying to create sharp detail, and it does so by creating halos, as you can see here. So we have this little dark tracing around the dark checker, and we've got this light tracing around the light checker. If you want to downplay the halos then you can switch to bicubic smoother, which is a kind of compromise between bicubic and the bilinear that we saw before, and we end up with less pronounced halos. If you want bigger, badder, halos then you switch to bicubic sharper. And you can see that we have some very dark halos indeed around the dark checkers, and some pronounced light halos around the light checkers. And that's going to result in what appears to be sharper details still, which is why it's the auto setting, so if you leave re sample set to auto, then Photoshop applies bicubic sharper.
When you down sample an image. Now I'll go ahead and switch over to the newest option, Preserve Details, and you can see that it results in these pronounced halos as well. And in fact it creates a very nearly identical effect to bicubic sharper, where these checkers are concerned. And in my test the only difference that I've found is it tries to run some shape analysis as well, which is why I've managed to achieve some pretty interesting results. By downsampling using preserve details so you might want to keep that in mind.
Alright now for the upsampling, I'm going to switch over to gray checkers small.tif and its a small reversion of the checkers we're still seeing it at the 200% view size. And I took this one and I upsampled it using all of the interpolation settings to 576% just so that we have a fixed amount. And so I'll go ahead and switch over to that version of the file, and I will zoom in as well. Now when you run nearest neighbor again, either a color wins or a color loses that's all that happens there's no averaging going on. Because we're upsampling even though its not a multiple of 100% everything looks pretty darn uniform although there are some differences in the size of the checkers.
Bilinear just goes ahead and runs sets straight averaging as you can see, and as a result, we get some very soft gradient transitions right here. And as a result, it can be very useful, by the way, if, during a down sample or an up sample, you end up getting too sharp of a result. Bicubic doing the same thing, as we saw before. It's drawing halos around each one of the checkers, and we also have some blur in between the checkers just as we do with bilinear.
If you want to downplay those halos, then you can switch to Bicubic Smoother. If you want to emphasize the halos, then you swicth to Bicubic Sharper. And then finally, we have these ultra halos right here. That are created by Preserve Details, and again, Preserve Details is also doing some shape analysis, so it does a good job of upsampling things like circles and diagonal lines, that are not naturally expressed by square pixels, which is why it's the automatic setting. So, if you leave Resample set to Auto, when upsampling, then Photoshop applies the Preserve Details option.
Now what's interesting about this, take a look at this. Previous versions of Photoshop automatically applied by Cubic Smoother. Which provides us with some very soft transitions. Now it applies preserved details, which provides us with some very sharp transitions. So we've gone from one of the softer settings, to one of the sharper settings. Just something that I want you to be aware of. So that's how the various interpolation methods work. In the next movie, I'll show you how to apply them when downsampling a photographic image.
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