Making the Dirt Blend Map
Why would we want to add dirt to our 3d objects? Adding dirt to an object is very important like all the other individual map types. In real life no object is perfectly clean, objects collects dirt one way or the other, softer stable objects such as a mirror or car paint would collect less dirt than an unstable rougher surface such as a tree bark, concrete, or clothes simply because dirt would slide off more from a stable surface and a rougher unstable surface would have very small bumps and holes hat the dirt could stay in. The pattern that the dirt has also depends on the surface is wet or dry, like a shiny new car paint or a mirror would not collect much dirt if dry simply because the dirt would not stick to it much, most of it would slide of but once the car or the mirror is wet the dirt would stick to it and form a different pattern than the dirt collected by a rougher unstable surface, why do you think the dirt of a mirror mostly forms the shapes of water droplets?.
What is a dirt blend map? The dirt bend map is a mask map for a blend type material in 3d max, max uses the information in this map to blend two individual materials together, the white areas represent one material and the black areas represent the other and the in between colors represent the amount that one material is blended with the other. I personally like painting the dirt using dark color tones, therefore the white color tones will have more of the material with our leaf maps applied
and the darker colors will have a dirt shader that were going to make in a later section of the tutorial.
First of all before we start making the dirt map, we need to decide what would be the best approach for the given object. The key to determining the amount of dirt to add to a material is to analyze the bump map, the bump base layer has a subtle noise pattern applied to it therefore it means that it would collect dirt but only at a subtle amount but on the other hand the leaf object has scratches and is damaged in a few areas, the brown damaged areas are a little more unstable means it would collect a little more dirt, and also some of the dirt would stick on some of the scratches but our leaf has seen some rain in the past days so therefore the most noticeable dirt will have the shape of water droplets and were also going to add dirt to the wet fingerprints in the specular map.
To start of create a new set and name it dirt map, create a new layer inside the dirt set and name it dirt level, now change the foreground color to a value of RGB:225 and the background color to RGB:190, control click on the specular level layer to make a selection of the leaves, go back to the dirt level layer and apply a cloud filter.
This time were going to be copying layers from our specular set since the colors in the specular map are close to the colors we want for our dirt map, were going to take some of the layers going from bottom to top, first off duplicate the pattern detail specular layer and move it to the dirt set, rename it to pattern detail dirt, open the hue/saturation
and change the lightness to 30, now what we want to do is just erase a few areas therefore not all the pattern would have dirt, I personally like to use a fingerprint brush as an eraser, that way it would be as some one scrapped off some of the dirt but if you want you could use a regular brush with some scattering, set the opacity to 50, just erase some of the areas the goal is to make the dirt look more randomly placed.
Make a duplicate of the brown damage specular layer and move it to the dirt set, rename it to brown damage dirt, change the lightness level to 45 and erase a few areas as well.
Do the same for the leaf pattern specular layer, the colors are ok already we just need to erase some of its areas here as well, completely erase at least about 50 percent of the pattern for this one.
Do the same for the center root specular layer, since this area is bumped down than more dirt will be collected by those areas unlike the leaf pattern and pattern detail layer. Therefore leave the colors for this layer as they currently are,erase random areas for this one as well.
Duplicate the fingerprints wet layer and move it to the dirt set, rename the layer to dirty fingerprints, open the hue/saturation, give the lightness an amount of -50, now just erase a little bit from each fingerprint.
Duplicate the scratches specular layer, move it to the dirt set and rename it to scratches dirt, the color tones are fine as they are, like all the other duplicated dirt layers, erase some of the areas to make it less uniform. On the left is a screen of the current state of the dirt map.
Now create a new layer above the rest in the dirt set, name this layer "center dirt", because of the shape of the leaf witch has a little bit of a "v" the leaf would be collecting more dirt on the top side in the center vain and also because of the thickness of the center vain could make it more probable for dirt to stay on its sides, and we some dirt on the bottom vain
as well but at a lesser amount, take note that the leaf on the right is the top side in the 3d model and the one in the left is the bottom side of the 3d model, so well be adding more dirt to the leaf on the right than the one on the left, for this were going to need a reference so move the wire reference layer on top of the dirt set, change the foreground color to an RGB:100, give the brush a size of 10, opacity to 25, flow to 50, in the brushes tab use a scatter amount of about 300 and pick dual brush number 60, decrease the spacing in the dual brush parameters if necessary. Using the reference start painting on the sides of the center vain of the leaf in the right try not to paint on the center root as much as you can, after you finished painting on the right change the foreground color to a value of RGB:130 and do the same for the leaf on the left. After your finished move the wire reference to the bottom of the sets and hide it for now. Use the following image as a reference for painting the center dirt
For the last dirt layer were going to make dirt in the shapes of water droplets, so create new layer and rename it to "droplet dirt" place it above the rest of the layers in the dirt set. Change the color to pure black, brush size to about 100, opacity to 75 percent, flow to 20 percent, in the brushes tab change the scattering to about 500 and use dual brush number 20, witch already look like the type of dirt water might leave behind, now paint this dots all throughout the leaf surface, increase the brush sizes to make bigger droplets as well. After your happy with droplet amount use the smudge tool in order to make some of the droplets appear as if they left a path behind them as well, for that you would have to have to increase the strength to 90 percent and make the brush size about the same size as the droplets, just click and drag beginning from the middle of a droplet and pull it toward the direction that the given droplet came from to create the water path effect, after you finished duplicate the droplet dirt layer and merge it down to make the droplets more pronounced, use the following image as a reference for the droplets and that finishes off the dirt map!.
Here's a render with the added dirt map, now you can see he essential difference that dirt plays on our surfaces, this added a whole new level of realism to the leaf, and it also helped make the specular reflections look more subtle on dirtier areas therefore taking it further away from the plastic look.