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So those of you who watched the previous exercise and are sitting there going, I knew was not going to learn anything from that, what in the world? I mean, now I know that you can't drop below 0.3 pixel and get in the effect out of Gaussian Blur. Who cares? But yet you still are watching me. In case you fall in to that demographic, let me assure you its still highly theoretical information, but it goes to the to the heart of how Photoshop works. I cannot stress this enough. Back in the old days programs with blur images, this was before Photoshop, they would blur images by assigning a linear blur and then Photoshop came around and offered the Gaussian Blur and it made all the difference in the world.
I know that's hard to believe, but let me show you, what's up here. As I say its very important to understand this whole Gaussian luminance distribution curve in order to understand whats going on with sharpening inside of Photoshop. So here I am working inside image called Gaussian demo.PSD found inside the 03 sharpen filters folder. I'm going to go over to the Layers palette, just to confirm that I've the Background layer selected. So we have got the rectangular area black in the left, a rectangular area of white on right. How is that for narrating the obvious? Lets go ahead and hide the Layers palette for a moment.
I'm going to go up to the Filter menu and I'm going to choose Blur and I'm going to choose Box Blur. A Box Blur even though it was only added like a few years back inside a Photoshop its an old school blurring tool. This is the way other programs used to work back in the old days. It assigns a linear blur, so I'm going to go ahead and choose the command. And I'm going to take the Radius value- you notice that it looks just like the Gaussian Blur dialog box- I am going to take the Radius value up to a 140 pixels, so something really large and the idea- by the way, this image measures 800 pixels wide.
So we are going to consume an area of about 280 pixels in the center here because Radius value times two gets you to the diameter. So about 280 pixels worth of drop off in the middle of this image and I'll go ahead and click OK. So its a zip we have converted what used to be a black and white image into a black and white gradient. Now with the slope right here in the center portion of the image. So I'm going to bring up the Layers palette, I hope this make sense. I have got a couple of graphs going on, all these other layers are graphs.
So I'magine that we are to graph the image and anywhere where the image is black, we would graph those pixels to the bottom of the image and anywhere where the image is white we'd graph it to the top and then any gray values in between would be graphed in between as well. So let me show you what I'm talking about. I'll turn on original and this original version of this image. So if I go ahead and undo the modification, black over here on the left, white over here on the right, so I'll press Crtl+ Z or Command + Z again to redo that Box Blur that I've applied, so here's my graph.
So all these pixels used to be black, hence this horizontal line along the bottom of the image, all these pixels used to white, hence this line across top of the image and there is our drop off in between. So it's a cliff essentially between those two extremes. That's the way the image used to be. I'll go ahead and turn that off and I'll turn on Linear slope, this is the way it is now. So just these pixels over here are black. These pixels over here are white. And I can confirm that by the way by getting my Magic Wand Tool. I'm going to go and switch over to the Magic Wand, make sure tolerance is set to zero, anti-alias is off.
These are not default settings by the way, so you would have to change them if you are following along. Contiguous is turned on, Sample All Layers is turned off, so settings as you see them. Background layer is selected. I'll click right there and you can see that those are the black pixels. So sure enough, my graph is accurate and these guys over here are the white pixels and in between the white pixels and, Shift-click over here, the black pixels, it's the area of grey pixels that has the linear drop off, notice that. There is a very clear point at which the gradient begins and the gradient ends.
So I'll go ahead in back step to get rid of those selection outlines. And the reason that this is important to know the fact that we have this point of which the gradient begins ands ends here is because, I'll go ahead and turn off the Linear slope, that means that we have a harsh transition at the point at which the blur begins at the point and the point at which the blur ends. So this is not a good blur. If we were to use this blur as a drop shadow for example, we would get a very sharp transition at edge, at the outer edge of the drop shadow, which would defeat the purpose since the drop shadow's supposed to look soft and it would no longer look soft, it would look sharp thanks to that linear distribution.
Lets go ahead and undo the Box Blur. And the solution is Gaussian Blur. I'm going to go up to the Filter menu with the Background layer still selected, go to Blur and I'll go ahead and choose Gaussian Blur and I'm going to apply that same value, 140 pixels. Now notice something right off the bat, I think you can see this, as I was saying this is an 800 pixel wide image and yet just about the entirety, with just a few edge pixels intact, is taken up with this blur. Even though if you multiply a 140x2, you still get 280 and yet we are taking up the entire 800 pixels, almost just a few pixels on the side left over. And that's the function of the spreading that is occurring thanks to Gaussian Blur, the Gaussian distributions.
I'll go ahead and click OK to accept that modification and you can now see that we have a much softer effect and that the colors are distributed not like this any more, not like the Linear slope, they are now distributed like this. We now have a Gaussian slope and notice what happens is that the colors transition very slowly at the beginning, more rapidly in the middle and very slowly at the end one again. If you want to confirm that, go ahead and bring up the Color palette and you can see that my foreground color is currently a 100% black.
I'm going to grab my eyedropper and if I click over here on the far left side of the image, watch this value right there, watch that 100% value, what is currently 100%. If I click and hold on far left side of the image, its still says the100%, but as I move, I'm moving my mouse very slowly, notice that there is 99 and there, pretty soon, we'll see 98, then well see 97, 96, 95, things are going more and more rapidly and now notice its going very rapidly. We have a very rapid transition between these colors and now notice it's dropping off very, very slowly again and I'm still dragging my cursor over to the right and then finally we go from one to zero.
So very slow transitions, that is at the edges, and the reason for that is because you want to have a gradual drop off so that your drop shadow, once again, just by way of example, doesn't look like it has a crisp, clear edge to it, instead it appears to just gently fade away. That gives you much more naturalistic effect and much more organic effect and that is like what I'm calling the Gaussian luminance distribution is so very important to the realism to the credibility of images that you produce with Photoshop.
Alright. So I'm going go ahead and hide that Color palette and just in case this graph isn't totally doing it for you, maybe this version will. This is my Gaussian black and white version of the graph. So basically the white is very slowly growing to take up what used to be black space. Another way, I don't know if that helps. Just another way of viewing the image, and probably the best one is this guy that I came with here. So there is the Gaussian slope with the Gaussian Blur in the background. In the next exercise, we are going to look at Unsharp Mask and then after that I'm going to show you how you can make Unsharp Mask all by yourself, if you feeling like a boy or girl scout, you can make Unsharp Mask using Gaussian Blur and nothing more.
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