Lesson 9: Layer Effects, including more cool text tricks. By now, you should be getting comfortable using a few layers, maybe even more than a few, to draw or paste parts of one image on top of another. But there are other interesting ways to combine layers. LAYER MASKS A Layer Mask is a way of making a layer transparent in some places and opaque in others. It's sort of like the opacity slider in the Layers dialog, but it's more powerful. A layer mask is a black-and-white image which is aligned with the layer it masks. Here's how it works: everywhere the layer mask is white, that layer is opaque. Where the mask is black, the layer is transparent. Where the mask is grey, the image is translucent: the darker grey the mask is, the more transparent the layer is. You can draw on a layer mask with any gimp drawing tool. The catch is, you can't really see what you're drawing: you can only see its effect on the layer, and the tiny copy of the mask in the Layers dialog. Confused? Let's do a few examples to make it clearer. Let's say I have a photo of my car: http://shallowsky.com/images/gimpcourse/lesson9/fiat.jpg and I put a label on it, using the text tool: http://shallowsky.com/images/gimpcourse/lesson9/fiat-labelled.jpg That text is kind of intrusive, though. What if I made it sort of fade into the background as it gets closer to the car? The first step is to create a layer mask: I go to the Layers dialog, right-click on the text layer, and select "Add Layer Mask..." A dialog comes up, but the defaults, of "White (full opacity)" is almost always the right thing to choose. This means that the layer mask will be white everywhere, so the layer will initially be visible everywhere. In the Layers dialog, now a new box appears to the right of the box for the text layer, showing a miniature preview of what the layer mask looks like (a white rectangle). The box is also surrounded with a white border, which means that the layer mask is selected: if you draw on the image right now, you'll be drawing into the layer mask, not into the layer. If you ever want to see what a layer mask looks like in full size, in gimp 2, go to the Layers dialog, right-click on the layer and choose Show Layer Mask. I don't know of any way to do this in gimp 1. Try it now (notice that the white border on the mask box in the Layers dialog turns a different color), then choose the same menu item again to go back to viewing the text layer normally. Now it's time to draw on the layer mask. I'll use the gradient tool, to make a fade that goes from white (fully visible) at the top of the layer to black (transparent) on the bottom). I select the gradient tool in the toolbox: it looks like a horizontal fade from black to white (maybe with another color in between, depending on gimp version). There are tons of tool options: for now, I want all the defaults: Mode Normal, Shape Linear. The normal way to use the gradient tool is to mouse down at one end of the layer, then drag to the other end. I want to fade from the foreground color (black) at the bottom to the background color (white) at the top, so I'm going to click at the bottom of the text layer, then drag straight up. When I let go, the layer mask is filled with a gradient, where the gradient is darker, toward the bottom of the text, the text will be more transparent. Like this: http://shallowsky.com/images/gimpcourse/lesson9/fiat-gradient.jpg If I "View Layer Mask", this is what I see: http://shallowsky.com/images/gimpcourse/lesson9/fiat-gradientmask.jpg while my layers dialog shows a small preview of the mask: http://shallowsky.com/images/gimpcourse/lesson9/fiat-layersdialog.jpg It's sometimes confusing to have a layer mask selected. When you're done drawing on your layer mask, try to remember to click on the layer preview next to the layer mask, so that the mask isn't selected any more. Otherwise, gimp will give you weird complaints when you try to save as jpg, and you'll get confused (at least, I do) when you try to do anything with that layer. If you ever try to draw on a layer and nothing appears, one thing to check is whether you have a layer mask selected, instead of the layer itself. BUMP MAP Bump Map is a built-in gimp filter which uses one layer to generate a 3-dimensional lighting effect on another layer. It comes in handy for all sorts of projects, but especially for making text. I'll start by making a new image, and using the Bucket Fill tool to fill it with a pattern. Then I'll put a layer of white text on top of it: http://shallowsky.com/images/gimpcourse/lesson9/bumpmaptxt.jpg Now I'm going to use the white text as a bump map for the woodgrain pattern. I select the woodgrain background layer in the Layers dialog, then go to Filters->Map->Bump Map... The Bump Map dialog comes up (in Gimp 2.2, it includes a preview). The dropdown at the top lets you choose which layer will create the shape of the bump. It can even be a layer in a different image, as long as that image is already loaded in your current gimp session. You can adjust lots of different parameters, such as where the light source appears to be coming from (that's Azimuth), how high the bump will be, and how wide it will seem to be. Play around with the parameters, and try it. The background layer will change to include the "bump" generated from the text layer. The text layer is still visible: you may want to toggle it off so that you only see the bump map. Here's an example: it: http://shallowsky.com/images/gimpcourse/lesson9/bumpmap.jpg If you want a smoother bump, use gaussian blur to blur the edges of the text layer before running the bump map. Like so: http://shallowsky.com/images/gimpcourse/lesson9/bumpmapblur.jpg You can run bump map on colors other than white, but usually it works best on white. Experiment with it to get just the effect you want. LAYER MODES You may have noticed the Mode dropdown in the Layers dialog, and wondered what that was. Layer Modes control how a layer is combined with the ones below it to produce the total image you see. Normally (in "Normal" mode), you see all of the layer on top; if there's anything still transparent, then you see pieces of the next layer down; if there's still anything transparent, you see the the next layer, and so on. But gimp can combine layers in ways more complicated than that. For instance, for each point in the image, it might show you the top layer minus the second layer, divided by the third layer. Why would you ever want to do that? It turns out there are some interesting effects you can do by combining layers in odd ways. Let's say I start with a white background layer; then, starting with a new transparent layer, I use the pencil tool to write some blue text: http://shallowsky.com/images/gimpcourse/lesson9/gimptxt.jpg Then I make a drop shadow, then blur the original layer: http://shallowsky.com/images/gimpcourse/lesson9/gimptxtblur.jpg By playing with layer modes, I can change this in interesting ways. For example, with the blue layer selected, if I change the mode to Divide, the color changes and I get this odd effect, somewhat 3-d effect: http://shallowsky.com/images/gimpcourse/lesson9/gimptxtdivide.jpg Screen mode gives me a different 3-d effect: http://shallowsky.com/images/gimpcourse/lesson9/gimptxtscreen.jpg Difference: http://shallowsky.com/images/gimpcourse/lesson9/gimptxtdifference.jpg Addition: http://shallowsky.com/images/gimpcourse/lesson9/gimptxtaddition.jpg Now for some even weirder effects: I'll turn the Background a medium grey (using Levels or Bucket Fill), then try some different modes on the blue blurred text layer: Divide: http://shallowsky.com/images/gimpcourse/lesson9/gimptxtgreydiv.jpg Dodge: http://shallowsky.com/images/gimpcourse/lesson9/gimptxtgreydodge.jpg Addition: http://shallowsky.com/images/gimpcourse/lesson9/gimptxtgreyadd.jpg Difference: http://shallowsky.com/images/gimpcourse/lesson9/gimptxtgreydiff.jpg If you wanted to use the result of one of these, you could use "Select by Color" to select out the grey background, and Edit->Clear it to leave you with just the text. Here's the Addition one: http://shallowsky.com/images/gimpcourse/lesson9/justgimptxtadd.jpg Don't worry if you don't understand exactly what each mode does. Most people don't. The important thing is to know that Modes exist, and that you can use them to combine layers in interesting ways. This means that (a) you can play around with trying different layer modes to see what they do, and (b) you can follow tutorials on using layer modes, such as these two: http://at8.abo.fi/~mwikholm/com/gimp/tutor/glass http://gug.sunsite.dk/tutorials/tomcat1/?PHPSESSID=cbe351c9a3609daeff9af437600297ea Here's a discussion of what some of the layer modes do mathematically, for those so inclined: http://www.pegtop.net/delphi/blendmodes/ It's oriented toward Photoshop, not Gimp, but as a Gimp user you can very often follow Photoshop tutorials -- the two apps have many of the same capabilities. Homework: Use any combination of Layer Masks, Bump Map, and Layer Modes to create something interesting from an image composed of several layers. Doesn't have to be text: you might be surprised what you can do starting with just a mouse scribble. Next Lesson: Stitching Panoramas from Multiple Images.