Stage 1- lighting
• I have decided on my lighting setup and framing. I want the fruit mostly top lit, and given that we are indoors and I want to use natural light, there is only one solution- mimic a skylight.
• First I created a physical sun and sky system, then cut a skylight size hole in the ceiling geo.
• Next I place a mental ray area light in the gap and map a portal light to collect the rays and bounce them down into the room –
• I am very fussy with the rotation of the sun, -72 degrees in X gives me just the right shadow falling across the fruit to creating a nice shadow. This will be the only light casting shadows
• I apply a matte white mia-x shader to all the objects for lighting evaluation
• I need some fill light for the tile wall so I decide for 2 spotlights, one either side –
For each fill, I map a seperate gobo that I have hand painted in photoshop. I want it to feel like there is more than one window in the room and hint that there might be some venetian blinds on them. Here is how this looks –
Lighting done for now, time to sort out all the shaders.
Stage 2 – shader building
Final daylight render – no grapes
I wont talk too much about the fruit textures or the basket because that is in a separate texturing post but its worth mentioning the other background stuff as I experiment alot with procedurals.
• For the benchtop, I use an mia-x and map a 3D granite procedural to the diffuse colour. The granite has basic swatches for the cell colours but for the filler colour I map in a grungy scatches image to break it up a bit. I use variations of this grungy image for the bump and spec also.
• For the glass bottle, I use the ‘interfaces’ technique from the mia-x manual but it gets its slight blueish look from a ‘use colour at max distance’ swatch. I achieved the soft specular highlights on the bottle by mapping a cloudy texture to the gloss on the air-glass interface shader.
• for the caustics through the bottle, I make a new spotlight just dedicated to caustics and light link it to just the benchtop, the tiles and the bottle.
I focused this light quite tightly in on the bottle from the same position as the right fill light. I then set it as a photon emitter.
Up until now I have avoided building a grapes shader, I have placed them on their own display layer and hid them out of the render. The grapes tend to hide everything else and I wanted the above hero render to show off all the other fruit shaders. This meant adjusting some of the fruit positions so that were not floating in mid-air.
• DOF – I use a bokeh lens shader for depth of field using a locator to measure the focus distance. This has a HEAVY impact on render times when using high enough samples to achieve a clean enough result. In fact, the render time on this frame went from 12 odd minutes to over 10 hours! My render machine is a 3 year old imac with a 2.8 Ghz processor with 4 cores.
I will need to find a DOF workaround because I need to do more renders and nobody has that kind of time. This is the only render that will have genuine DOF.
Stage 3 – SSS, more shader tweaking and alternate lighting scenario
Final Daylight render- Grapes Hero
As I said above, until now I have avoided the grapes. It is time to set up a shader for them.
I have been reading about a technique where you can exploit the sub-surface scattering properties of the fast SSS shader combined with the flexibility of the specular features of the mia-x. This is done be piping the SSS shader into the ‘additional colour’ node of the mia-x.
I set up the SSS as suggested in the mental ray manual, tweaking each SSS layer at a time and tweaking the colour until I achieve the right translucent effect I was after. Running it into an mia-x meant that I could adjust the specular reflective qualities inside the mia-x. I also use a procedural map for breaking up the spec highlights to get a ‘frosted’ result. This method did produce really photo-realistic grapes but making tweaks was very painful due to the expensive render times. I would not use this method again unless I knew I had lots of time to play.
I also added some nurbs sphere water droplets, snapping them to vertices on some of the grapes. I made a transparent shader, but initially they were not showing up enough, I fixed this by overdriving the value on the reflections and dropping the transparency to less than 1. I think I ended up at .98 just to allow a little diffuse to show up. It is still very subtle but worth it.
For the branch on the grapes, I use the approximation editor to tesselate the low res geometry. I am amazed at how quickly and easily this fixes the faceting!
I decide on this camera angle as it not only shows the grapes off nicely, but also all my hard work UV mapping and texturing the wooden basket and the grapes branch.
As I said before, I needed to find a workaround for DOF as the bokeh lens shader has been unmanageable for render times.
I resort back to my class notes on rendering a camera depth pass. The formats and naming conventions and framebuffers confuse me a bit and it takes me a while to figure out that I must use batch render but eventually I get a nice Z-depth mask I can use in photoshop-
In photoshop, I duplicate the RGB layer and load the camera depth alpha as a layer mask, then using the lens blur feature I tell it to use the layer mask and use the blur focus distance to keep the foreground sharp and just throw the background out of focus.
For a ‘cheap’ method, it works OK but I do find that you have to keep the blur radius pretty low or you tend to get some weird edges. I keep it very minimal but just want to avoid that classic CGI look of have infinite sharpness. Having tiny noise setting of 1 is just enough to prevent excess banding.
This DOF does not look anywhere near as good as my first render using bokeh but 10 hour render times are not my thing 🙂
Alternate lighting scenario
Final Moonlight with downlight
I pushed my daylight scenario pretty far but I wanted to have a go at more of a nighttime lighting solution. Here is a screenshot of my lights labeled so that I can describe their function-
Light A – is the same sun and sky system as the daylight but with the direction at much more acute angle, the colour turning quite blue.
Lights B and C – spotlights mimicking warm under-cabinet lighting. Colour set set to yellow/orange, placed close to the wall. Cone angle and penumbra tuning to show visible soft edges.
Light D – caustic photon caster
Light E – large cone, low intensity spot light-linked just to the benchtop to fill and reduce the dark shadows cast by the basket. I also linked the pear as it was looking a bit dark in the low specular areas. Here is a before and after render of this fix –
Light F and G – blueish coloured ‘moonlight through window’ fills – mapped with same blind shapes gobos as used in the daylight renders.
For this lighting setup, I found that I also had to change some of the shaders slightly. For instance, I strongly reduced the bump on the benchtop because with closer direct lighting it was too artificially bumpy and catching hot spots.
As with my hero grapes render, I rendered a camera depth channel and applied a lens blur in post through the mask –