Making the Bump Map
First of all what is a bump map? We use bump mapping order to make a surface appear as if it were irregular and bumpy, bump mapping should be used in almost every material even if the bump amount is very subtle otherwise a surface would appear to be perfectly smooth such as the surface of a mirror or plastic, bump mapping can be used to add additional detail to a surface such as a scratches and dents but bump mapping has its limit when it comes to depth, it will look good when you used it for small details but once you try to use bump mapping for making details like the buttons on the remote control for example its
will probably end up looking rather flat because bump mapping does not change the way the surface is it just changes the way that surface interact with light to make areas appear bumped down or bumped up. For making details such as the buttons in a remote control you might consider modeling the buttons or using displacement mapping, since displacement does indeed change the way a surface/geometry is composed.
How does the bump map work? Like most of the other map types instead of the color map a darker area in the map will have a negative influence and the lighter area in the map will have a positive influence, therefore darker areas in our bump map will appear to be bumped down (negatively) or bumped up (positively). So if we add scratches to our map than we would make them darker in order for them to be bumped down and other things such as the root patterns would look better if they were bumped up therefore those areas would have a lighter color in our bump map. The way this rule applied to other map types for example in a specular map the negative areas would be less reflective and positive areas are more reflective. Most of these type of maps don't require you to have any color information in them, we will only use black and white colors for those maps.
Here's an example of a bump map and the effect this has on a 3d surface, as you can see, the darker areas of our map are bumped down negatively on our 3d surface therefore making it look as if the surface had small holes in it, and the areas that are lighter in our map have a positive influence in our surface therefore making those areas appear to pop out.
Why not just use the color map as our bump map and move on? This might work fine in some occasions but not on most, we know now that a bump map gives irregularity and bumpiness to a surface but by simply using our color map as our bump map some information in our color map would be used for bump mapping calculations that we don't really want to be included, what we try to do when using bump mapping is capture the way that surface would feel in the real world, now we would not really feel the color of a surface right? Therefore color changes should not be included in a bump map, what should be included are areas that you would feel or know that are distorted such as the pattern of the surface, a scratch, or dent for example. That's why it's very important when making a color map as we just finished making to keep all the major details separated in layers as wee did with the color layers, therefore when we start making other map types we could simply duplicate that detail that you want to add to your bump map without having to deal with the rest.
Now we're ready to create the bump map, making it wont take nearly as much because were going to duplicate layers from the color set and move them to the bump set to either be bumped down or up.
We'll start by creating a new set, name this set "bump map", create a new layer inside this set and rename this layer to "bump base", control click on the base color layer in the diffuse color set to make a selection of the leaf, now fill this selection in the bump base layer with a color value of RGB:150, this will produce a gray color, the reason why we are not using completely white or black as our base color is that things are going to be bumped down and bumped up, we'll give darker color tones to the things we want to bump down, things such as a scratch and lighter colors to things we want to bump up such as parts of the leaf pattern.
Add a noise filter to the base layer and give it a value of 2, now add a blur more render filter to it. This will just break up the surface a bit so it does not look perfectly smooth.
Make a duplicate of both the leaf pattern layer and the pattern detail layer and move the duplicates to the bump map set, rename the layers to leaf pattern bump and pattern detail bump. Set both of there blending modes to normal, now change the opacity of the leaf pattern bump layer to 100 percent. Select the pattern detail layer and open hue/saturation, set the saturation to -100 to remove all the color information since its not needed in a bump map and it makes things easier to work with, change the lightness to 65 since we only want the pattern details to be slightly bumped up therefore it only has to be a little brighter than the bump base color, now open the hue/saturation for the leaf pattern bump layer, change the saturation to -100 and lightness to 80. Now in order for the leaf pattern bump not to start up that drastically from the center vain you can give the edges a slight blur with the blur tool.
Make a new layer and call this layer "center root bump", basically we want to make the area were the vain is supposed to be a little rougher so therefore were going to paint a little bit of a bigger noise pattern to it. Select your brush and change your foreground color to a RGB:125, change the size of the brush to about 15, spread the flow to 50 percent, in the brushes tab increase the scattering to 350 and make sure dual brush number 60 is activated, now use the white lines as a reference to paint the areas between them. Use the following image as a reference for the changes made thus far to the bump map.
Make a duplicate of the brown damage layer in the diffuse color set, rename this layer to brown damage bump, unlike the red damage the brown damage has noticeable surface distortion were it is, therefore we're going to give this layer a slightly
lighter color than the bump base for it to be bumped up a bit, move the layer up so its above all the bump layers inside the bump set but below the leaf pattern bump layer. Open the hue/saturation for the brown damage bump layer and se the saturation to -100 and lightness to 70, this will make it a little brighter than the pattern detail but a little darker than the leaf pattern.
For our last bump detail were going to add some scratches to the leaf surface, so make a new layer and name this layer "scratches", position this layer above all layers, the scratches need to be bumped down so therefore we need to change the foreground color to an RGB:75 change the brush size to 20, in the brush tab increase the scattering to about 400 and in the dual brushes pick number 112 witch already look likes a scratch on its own . Now paint over the surface the way you see fit, but make sure you don't paint in the edges. After you finished with the scratches change the dual brush to number 60 and the flow to 20 and create a few more scratches that are more of a circular pattern instead, now apply a Gaussian blur to the scratch layer with a value of 1 to get rid of some of the sharp edge. Here's a shot of the completed bump map!
When you add details such as a scratch to the bump channel only, the scratch wont look as good, we need to connect the scratches to the specular, color and diffusion maps as well. For example the scratches in this case would have a lighter color, not as much light enters a scratch so therefore the scratches will have a lower specular amount. Therefore were going to make a duplication of the scratches layer and rename it to "scratches color" and move it to the diffuse color set, for now hide the bump set to be able to see the color maps, move the scratches color layer so its on to of every other layer in the diffuse color set, because we need scratched areas to look lighter invert the color of the scratches (image>adjustments>invert), change the blending mode to luminosity, we also need to do the same for the "center root bump" layer in the bump set, so make a duplicate and rename to center root color and move it to the diffuse color set, move it so it's on top of the base color layer and below the rest of the layers, invert it's color, change the layer blending mode to luminosity and give the layer an opacity value of 75 percent. Here is a screen of the updated color map, now that we finished translating some of the bump map information to the color map were ready to start making the specular map.
Here's a render of the leaf with the added bump map.