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The "bell-shaped" Gaussian Blur

From: Photoshop CS3 One-on-One: Beyond the Basics

Video: The "bell-shaped" Gaussian Blur

Alright so here is how things are going to go down. In the first portion of this chapter I am going to introduce you to what I consider to be a few of the best of the blurring and averaging functions inside of Photoshop and we are going to approach the commands on an analytical level so we can figure out how they work. And then in the second portion of the chapter I will show you the fun, creative and very practical applications of these filters. Yes they are all filters because they are edge detection functions after all. I am working inside this analytical illustration here rectangles.psd inside the 12 Blur Average Folder.

The "bell-shaped" Gaussian Blur

Alright so here is how things are going to go down. In the first portion of this chapter I am going to introduce you to what I consider to be a few of the best of the blurring and averaging functions inside of Photoshop and we are going to approach the commands on an analytical level so we can figure out how they work. And then in the second portion of the chapter I will show you the fun, creative and very practical applications of these filters. Yes they are all filters because they are edge detection functions after all. I am working inside this analytical illustration here rectangles.psd inside the 12 Blur Average Folder.

Pretty simple little diagrams to start with, just these rectangles at again sort of a textured background and altogether there is four of them two side by side at the top and two side by side below so a pair up and a pair down. And of course I have sized my window on screen here so that I can use the Home and End keys to bounce back and forth. Look at that scroll bar, Home and the images exactly aligned with each other for comparative purposes don't you know. Alright let's start with the upper left hand image.

It should be selected by default but let's just check. I will bring up the Layers palette. Sure enough there it is it's 1TL meaning top left. We also have two top right, three bottom left and four bottom right. So go ahead and make sure 1TL is active. I am going to press the F7 key to make that palette go away now because I have tucked my palettes away into these tiny little icons. I tell you what I am falling in love with that feature. It did take a little bit of time actually I have to tell you but now me and it I see marriage, baby carriage the whole thing.

Alright anyway and we got the top left image selected. I want you to go up to the filter menu now, choose blur and choose the boss of all the blurs this guy right here Gaussian Blur and it's not going to seem like much. This is a very simple filter as it turns out. All you have got is a radius value and it just blurs things. Big deal, big whoop but how it works is sort of key to understanding what's going on with filtering in general inside Photoshop. I did allude to it back when I was talking about unsharp mask and smart sharp in the Gaussian Blur function you might recall back in the previous chapter.

Anyway let's see what's going on with it. Go ahead and choose the command or if you loaded my Deke keys you can press Shift F7 in order to bring it up, that works too and I will go ahead and drag the preview over inside this little preview box. It's not all that necessary because we can see it out here as well. I am going to change the radius value it starts at 1.0. I mean it's the default setting, refractory default setting. It might appear something else for you, doesn't really matter. Notice that of course I mean this is not unexpected at all for you and lower values, you are going to do just a little bit of blurring so if you just want a slight panache of blurring then you can enter a very low radius value such as 0.3 that's about as low as I go.

When you drop to 0.2 and 0.1 you start to lose these radius effects it's basically what's going on. Now I am going to take it up and just sort of keep an eye on this. I am just pressing the Up arrow key to raise that value in 0.1 increments and now I am going to press Shift Up arrow to raise it in whole number increments until I get up to about here 20 pixels worth of radius and notice how blurry things are now. There are two things I want to point out about the Gaussian Blur. Why in the world is it called Gaussian Blur in the first place? Well it's named after this fellow this mathematician named Frederick Gauss in case you are curious and it's named after this thing he came up with which is the Gaussian bell shaped curves so the idea, notice I am kind of drawing half of a bell here.

Imagine this is the top of the bell and then I am dragging down like this and here is the bottom edge of the bell and then it goes over like this and then I drag back up. I just drew a bell. Do you see that? Think of the liberty bell there. So anyway the bell shaped curve just is one half, just that one edge of the bell like this and the idea is this the slope of the curve starts, the slope of the blur that is imagine that this blur right here is a slope. So when we are seeing the dark color, we are at the top of the slope, we are at the top of the bell and when we are seeing the light color we are at the bottom of the bell.

And so you start very slowly, the blur starts very slowly at the top of the bell here and then it goes quickly down the side of the bell at this point and then I accidentally click so that was why that changed that in that area and then it goes slowly at the end as well and that slowness at the end is the key factor. Notice what's happening inside of the dialog box here. You can see the edge of this layer blurring into this checker board and the checker board represents transparency. So it's actually blurring the layer into nothingness and in here we are seeing white in the background so it's blurring into the whiteness and you can't really see the edge, can you, that's because of this Gaussian bell shaped curve.

I will show you what it looks like if we didn't have that curve in the next exercise but just take my word for it for now. That Gaussian equation there is one of the things that makes Photoshop so great because there is applications out there that aren't capable of Gaussian equations and this means that we have very soft drop offs on screen and print and so on, so wonderful softness at the end of our blur. Go ahead and click OK in order to accept that modification. Now not only did we blur the contents of the layer, we also blurred the transparency mask that is to say we blurred the edges of the layer.

So if I went over here to Layers palette and I am going to go all the way down and click on the background layer and I am going to fill it with black, black is my foreground color right now you can see that at the bottom of the toolbox. So I am going to press Alt Backspace or Option Delete to fill the background with black so that you can see no matter what it's still blurring very softly into the background. No matter what I change the background to, this layer this top left layer 1TL is always going to blur very softly into it because the edges of the layer are actually blurred. Isn't that amazing? Alright I am going to undo that modification now if you don't want to work that way.

I will go ahead and back up and undo the application of the Gaussian Blur command to this TL layer as well and that automatically selects it. If you just want to blur the contents of the layer and not the edges of the layer, you want to keep them nice and crisp for whatever reason then you would go to this little Lock icon in the top left corner of the Layers palette here, this little checker board lock and click on it so that first icon to the right of the word Lock. Click on it, makes a little lock. That locks the transparency so it can't be modified.

Now let's just repeat the application, the Gaussian Blur filter by choosing it from the filter menu and notice this time it just blurs the contents of this layer and not the edges. Alright it turns out I don't want to do that, I want to go ahead and blur the edges too so I am going to undo that modification and check this out. There is a keyboard shortcut for accessing that transparency function right there and it happens to be the slash key. I just pressed the slash key, I didn't click on it. I just pressed the slash key the one under the question mark so slash turns it on, slash turns it back off. In case you need another keyboard shortcut smashed in your head there.

Alright so let's go ahead and reapply that Gaussian Blur filter to the layer and we get a nice soft drop off that is the amazing world of Gaussian Blur inside Photoshop. In the next exercise you will see what a world without Frederick Gauss would look like.

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This video is part of

Image for Photoshop CS3 One-on-One: Beyond the Basics
Photoshop CS3 One-on-One: Beyond the Basics

129 video lessons · 39092 viewers

Deke McClelland
Author

 
Expand all | Collapse all
  1. 1h 15m
    1. Welcome to Photoshop CS3 One-on-One: Beyond the Basics
      2m 5s
    2. Selecting glass and water
      5m 23s
    3. Establishing a base layer
      4m 0s
    4. The Color Range command
      6m 45s
    5. Selecting sparkles
      3m 19s
    6. Setting sparkles to Screen
      4m 19s
    7. Selecting and compositing hair
      2m 59s
    8. When Color Range falls short
      7m 25s
    9. Selecting a base channel
      4m 25s
    10. Enhancing the channel's contrast
      4m 4s
    11. Dodging the highlights
      5m 55s
    12. Putting the mask in play
      3m 20s
    13. Reducing the edge fringes
      4m 21s
    14. Adding a layer mask
      4m 53s
    15. Creating a gradient quick mask
      5m 26s
    16. Blurring the layer mask
      5m 51s
    17. And that's just the beginning...
      1m 15s
  2. 1h 13m
    1. Edge-enhancement parlor tricks
      1m 30s
    2. The subterfuge of sharpness
      3m 14s
    3. The single-shot sharpness
      3m 47s
    4. Unsharp Mask
      5m 17s
    5. Understanding the Radius value
      4m 31s
    6. Gauging the best settings
      7m 14s
    7. Sharpening the luminance data
      8m 25s
    8. USM vs. Smart Sharpen
      6m 0s
    9. Smart Sharpen's Remove settings
      6m 23s
    10. High-resolution sharpening
      6m 4s
    11. Leave More Accurate off!
      2m 29s
    12. Turn More Accurate on
      2m 58s
    13. The Advanced options
      5m 17s
    14. Saving Smart Sharpen settings
      4m 18s
    15. Accounting for camera shake
      6m 0s
  3. 1h 24m
    1. Why the heck would you blur?
      1m 20s
    2. The "bell-shaped" Gaussian Blur
      7m 16s
    3. The Linear Box Blur
      2m 58s
    4. Median and its badly named progeny
      6m 3s
    5. Surface Blur and the rest
      5m 36s
    6. The Motion Blur filter
      3m 2s
    7. The Radial Blur variations: Spin and Zoom
      5m 55s
    8. The Captain Kirk-in-love effect
      6m 50s
    9. Averaging skin tones
      6m 2s
    10. Addressing the stubborn patches
      6m 0s
    11. Combining Gaussian Blur and Average
      4m 8s
    12. Blurring surface details
      7m 2s
    13. Smoothing blemishes while matching noise
      7m 52s
    14. Reducing digital noise
      8m 22s
    15. Smoothing out JPEG artifacts
      6m 1s
  4. 45m 28s
    1. Behold, the layered composition
      1m 13s
    2. The Layers palette
      5m 8s
    3. Enlarging the hand
      4m 40s
    4. Erasing with a layer mask
      6m 28s
    5. Moving a layer
      4m 3s
    6. Combining layers into a clipping mask
      4m 42s
    7. Hair and stacking order
      6m 12s
    8. Adding a frame and expanding the canvas
      6m 2s
    9. Adding a vignette
      7m 0s
  5. 42m 27s
    1. Organization: It sounds dull, but it rocks
      1m 8s
    2. The terrible battle
      3m 3s
    3. Assembling the base composition
      5m 46s
    4. Adding adjustment layers
      4m 55s
    5. Creating a layer group
      2m 24s
    6. Grouping selected layers
      3m 13s
    7. Making the TV lines
      4m 17s
    8. Introducing layer comps
      5m 52s
    9. Saving your own layer comps
      6m 40s
    10. Final footnotes
      5m 9s
  6. 1h 23m
    1. Parametric operations
      1m 4s
    2. The power of blend modes
      6m 44s
    3. Changing the Opacity value
      5m 35s
    4. Opacity vs. Fill Opacity
      4m 37s
    5. Meet the blend modes
      5m 38s
    6. Blend mode shortcuts
      5m 52s
    7. The darkening modes
      6m 12s
    8. Tempering a Burn effect with the Fill value
      3m 53s
    9. Saving a blended state
      2m 54s
    10. The lightening modes
      4m 55s
    11. The contrast modes
      7m 13s
    12. The comparative modes
      7m 25s
    13. The composite (HSL) modes
      6m 2s
    14. The brush-only modes
      8m 11s
    15. Blending groups
      7m 10s
  7. 1h 27m
    1. At this point, there is a great shift...
      59s
    2. Messing with the masters
      2m 28s
    3. Scaling a layer to fit a composition
      6m 39s
    4. Merging clock face and cardinal
      2m 2s
    5. Rotating the minute hand
      7m 42s
    6. Replaying the last transformation
      3m 50s
    7. Second hand and shadows
      5m 0s
    8. Series duplication
      3m 23s
    9. Skews and perspective-style distortions
      6m 43s
    10. The envelope-style Warp function
      7m 32s
    11. Introducing the Liquify command
      5m 9s
    12. Adjusting the brush settings
      4m 2s
    13. Viewing layers and the mesh
      4m 18s
    14. Incrementally undoing undesirable effects
      4m 5s
    15. Twirl, pucker, and bloat
      2m 2s
    16. Push, mirror, and turbulence
      4m 37s
    17. Protecting regions with a mask
      3m 41s
    18. Applying a digital facelift
      10m 53s
    19. Saving and loading mesh settings
      2m 31s
  8. 1h 18m
    1. Planes and perspective
      1m 7s
    2. The Blue Gallery
      2m 47s
    3. Introducing Vanishing Point 2.0
      5m 30s
    4. Drawing out perpendicular planes
      6m 54s
    5. Exporting the gridlines to a layer
      4m 45s
    6. Cloning an image from one plane to another
      7m 58s
    7. Blending the image into its new home
      6m 31s
    8. Healing away the sockets
      7m 48s
    9. Importing a new image
      6m 20s
    10. Masking and shading the image
      7m 27s
    11. Flat in, perspective out
      5m 57s
    12. Adding perspective type
      4m 50s
    13. Swinging planes to custom angles
      6m 2s
    14. Wrapping art around multiple surfaces
      4m 35s
  9. 1h 15m
    1. Type: The great imaging exception
      54s
    2. Creating an independent text layer
      6m 39s
    3. Editing vector-based text
      6m 38s
    4. Working with area text
      6m 15s
    5. Resizing the text frame
      6m 4s
    6. Obscure but important formatting options
      7m 25s
    7. Text editing tricks and shortcuts
      9m 38s
    8. Adding a ghostly cast shadow
      6m 19s
    9. Backlighting the text
      2m 48s
    10. Creating type on a path
      7m 37s
    11. Pasting text along the bottom of a circle
      3m 50s
    12. Flip and baseline shift
      3m 15s
    13. Warping text
      3m 58s
    14. Scaling the warped text to taste
      4m 18s
  10. 1m 11s
    1. See ya for now
      1m 11s

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