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The interpolation settings

From: Photoshop CS6 One-on-One: Fundamentals

Video: The interpolation settings

This next topic is a little technical, but I think it's important to understand if you really want to come to terms with modifying image size in Photoshop. It's all about the methods of interpolation. Now interpolation is what Photoshop uses to decide how to rewrite the pixels in the image, either when you upsample or downsample a file. And it's all about taking the existing pixels in the image and somehow comparing them to come up with new pixels. To give you a sense of what I'm talking about, I'll go up to the Image menu and choose the Image Size command.

The interpolation settings

This next topic is a little technical, but I think it's important to understand if you really want to come to terms with modifying image size in Photoshop. It's all about the methods of interpolation. Now interpolation is what Photoshop uses to decide how to rewrite the pixels in the image, either when you upsample or downsample a file. And it's all about taking the existing pixels in the image and somehow comparing them to come up with new pixels. To give you a sense of what I'm talking about, I'll go up to the Image menu and choose the Image Size command.

When the Resample Image check box is turned on, you have access to this pop-up menu. By default in CS6, it's set to Bicubic Automatic, and I'll explain what that means in just a moment. But you can manually override this option if you want to by selecting any of these five interpolation options, Nearest Neighbor and any of the three manual Bicubic overrides. Now to give you a sense of how they work, I created a test file and this is it right here, just these nondescript gray checkers.

We're viewing the file at the 200% zoom ratio so the checkers are actually a little smaller than this. What I did was I went up to the Image menu, chose the Image Size command, changed this option here from Pixels to Percent and went ahead and dialed in a percent value of 72, and notice that, that changes both the Width and the Height values. Now by way of a little tip here; notice that when I switched the option to Percent, both of the values switched to Percent, if that's not what you're looking for, if you just want to change one of the values to something different, you press the Shift key while choosing a new option.

So in this case, I had the Shift key down when I chose Pixels, and as a result I can see that the Height of my image is going to decline to a 184 pixels when the Width is set to 72%. Then I went down to this pop-up menu and chose each of these options. Well just to save us time, let me show you what that looks like. I'm going to switch over to this diagram that I created, and here is each and every one of those manual interpolation settings shown in order. So we'll start right here with Nearest Neighbor. Notice that Nearest Neighbor doesn't attempt to do any real interpolation; it just keeps pixels or throws them away.

And as a result, some of my checkers are shorter or narrower than others, and so we get this kind of patterning effect that's known as aliasing. Nearest Neighbor can work well for highly graphic files, for example, screenshots. If you want to take a screenshot and expand it to 200% of its former size, then Nearest Neighbor would be the way to do it. That's about the only time I use that option, however, except I should say, for magnifying each one of these images. Notice that I have taken them all and scale them to 400% and I did that using Nearest Neighbor so as not to introduce any new pixels.

All right, I'll zoom into Bilinear. Bilinear is ultimately a simple averaging formula. And as you can see it ends up creating soft transitional pixels. But it doesn't do a very good job of maintaining detail, which is why Bicubic was invented. Now Bicubic is much more complicated. It uses a series of derivatives that you don't need to know anything about. But notice that what we get are these halos inside and outside of the checkers. So we get this kind of border pattern around the checkers and we get dark halos inside the dark squares and light halos inside the light squares.

Now if those halos end up being a problem, you can switch over to Bicubic Smoother which downplays the halos significantly. So you can see that we don't have nearly as much halo action going on. It's subtle but it's distinct. If you want more halo action--and the idea is the halos end up emphasizing edge contrast which creates the appearance of crisper detail, then you can bump things up by switching to Bicubic Sharper. Now I should say, when you're working with Bicubic Automatic anytime you downsample an image, Photoshop is going to automatically apply Bicubic Sharper with the assumption that you want crisp detail out of your downsampled image.

I've also created a demo file for upsampling. What I did this time was I switch to a smaller version of the checkerboard image. We're still seeing it at the 200% zoom ratio, and I upsampled the image to 576%. It just happened to work well for my demo file and came up with this composition here. I'll go ahead and zoom in--notice that this time around, things work out pretty well for Nearest Neighbor. Some of the squares are different sizes than others, but it's not nearly so noticeable. Where Bilinear is concerned, we end up with these soft, continuous transitions.

So it's almost like we've turned each one of the squares into a kind of gradient. We have the appearance of sharper detail because we have these dark halos inside the dark checkers and these light halos inside the light ones. Bicubic Smoother ends up resulting with less haloing and then Bicubic Sharper ends up resulting with even more haloing. Now when you're upsampling an image, Bicubic Automatic goes ahead and applies the Bicubic Smoother setting. The assumption being that you still want bicubic detail but you want smoother transitions.

So that's how the various interpolation settings work. In the next movie, I'll show you how they affect a photographic image.

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This video is part of

Image for Photoshop CS6 One-on-One: Fundamentals
Photoshop CS6 One-on-One: Fundamentals

100 video lessons · 57389 viewers

Deke McClelland
Author

 
Expand all | Collapse all
  1. 19m 15s
    1. Welcome to One-on-One
      2m 27s
    2. Opening from the Windows desktop
      4m 7s
    3. Opening from the Macintosh Finder
      4m 9s
    4. Opening from Photoshop or Bridge
      2m 45s
    5. Opening an image from Mini Bridge
      1m 16s
    6. Opening through Camera Raw
      2m 32s
    7. Closing one image and Closing All
      1m 59s
  2. 38m 14s
    1. Navigating your image
      40s
    2. The dark vs. the light interface
      3m 12s
    3. Navigating tabs and windows
      4m 32s
    4. Panels and workspaces
      4m 27s
    5. Zooming incrementally
      4m 29s
    6. Zooming continuously
      2m 43s
    7. Entering a custom zoom value
      2m 25s
    8. Scrolling and panning images
      2m 31s
    9. Rotating and resetting the view
      2m 11s
    10. Cycling between screen modes
      3m 10s
    11. Using the Navigator panel
      3m 38s
    12. Adjusting a few screen prefs
      4m 16s
  3. 45m 58s
    1. Digital imaging fundamentals
      1m 45s
    2. Image size and resolution
      3m 3s
    3. The Image Size command
      3m 27s
    4. Common resolution standards
      3m 20s
    5. Upsampling vs. real pixels
      4m 36s
    6. Changing the print size
      6m 16s
    7. Downsampling for print
      4m 12s
    8. Downsampling for email
      3m 11s
    9. The interpolation settings
      5m 22s
    10. Downsampling advice
      4m 36s
    11. Upsampling advice
      6m 10s
  4. 53m 17s
    1. The layered composition
      1m 40s
    2. Introducing the Layers panel
      4m 12s
    3. Adding, scaling, and aligning layers
      5m 27s
    4. Dragging and dropping layers
      4m 36s
    5. Stack, reveal, and rename
      2m 58s
    6. Opacity, history, and blend mode
      6m 5s
    7. Duplicating a selected portion of a layer
      5m 32s
    8. Applying a clipping mask
      3m 58s
    9. Blending inside a clipping mask
      4m 10s
    10. Finishing off your artwork
      3m 13s
    11. Creating a new layer and background
      4m 24s
    12. Layering tips and tricks
      7m 2s
  5. 26m 19s
    1. The art of saving
      54s
    2. Four things to know about saving
      6m 0s
    3. Saving layers to PSD
      6m 38s
    4. Saving print images to TIFF
      4m 48s
    5. Saving an interactive image to PNG
      3m 41s
    6. Saving a flat photo to JPEG
      4m 18s
  6. 19m 36s
    1. Honing in on your image
      1m 43s
    2. The new and improved Crop tool
      3m 35s
    3. Editing your last crop
      3m 1s
    4. Straightening a crooked image
      2m 29s
    5. Filling in missing details
      6m 44s
    6. Using the Perspective Crop tool
      2m 4s
  7. 42m 6s
    1. First, there is brightness
      2m 12s
    2. How luminance works
      4m 18s
    3. The three Auto commands
      3m 27s
    4. Automatic brightness and contrast
      3m 19s
    5. The Brightness/Contrast command
      2m 47s
    6. The dynamic adjustment layer
      4m 5s
    7. Editing adjustment layers
      3m 52s
    8. Isolating an adjustment with a layer mask
      3m 31s
    9. Introducing the histogram
      4m 58s
    10. Measuring an adjustment
      3m 34s
    11. Using the Shadows/Highlights command
      6m 3s
  8. 44m 33s
    1. And second, there is color
      1m 31s
    2. Identifying a color cast
      3m 34s
    3. Correcting a color cast automatically
      3m 57s
    4. Changing the color balance
      6m 10s
    5. Compensating with Photo Filter
      3m 11s
    6. Adjusting color intensity with Vibrance
      3m 29s
    7. Correcting color cast in Camera Raw
      5m 46s
    8. The Hue/Saturation command
      5m 26s
    9. Summoning colors where none exist
      4m 8s
    10. Making more color with Vibrance
      4m 27s
    11. Making a quick-and-dirty sepia tone
      2m 54s
  9. 55m 46s
    1. Making selective modifications
      1m 10s
    2. The geometric Marquee tools
      6m 1s
    3. Aligning one image element to another
      4m 59s
    4. The freeform Lasso tools
      3m 59s
    5. Polygonal Lasso tool and Quick Mask
      5m 19s
    6. Cropping one selection inside another
      6m 15s
    7. Creating rays of light
      4m 44s
    8. Quick Selection and Similar
      4m 11s
    9. Making it better with Refine Edge
      4m 56s
    10. Integrating image elements
      2m 39s
    11. Magic Wand and Grow
      5m 17s
    12. Refine, integrate, and complete
      6m 16s
  10. 53m 49s
    1. Your best face forward
      1m 0s
    2. Content-Aware Fill
      6m 11s
    3. Using the Spot Healing Brush
      5m 36s
    4. The more capable "standard" Healing Brush
      5m 55s
    5. Meet the Clone Source panel
      3m 53s
    6. Caps Lock and Fade
      4m 57s
    7. The Dodge and Burn tools
      5m 1s
    8. Adjusting color with the Brush tool
      6m 35s
    9. Smoothing skin textures
      5m 58s
    10. Brightening teeth
      4m 0s
    11. Intensifying eyes
      4m 43s
  11. 51s
    1. Goodbye
      51s

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