I have used Vray for most of my career and when I moved into Architectural Visualisation 3 years ago, it was definitely the dominant render engine. However, about half a year ago I started to hear a lot about Corona, so in my spare time I decided to try it and see how it compared to Vray. This project was just something I made up for these test purposes only and was not commercial in the slightest.
To light this scene I started with a HDRI map. I used the free Peter Guthrie HDR that comes with Corona, specifically 1347 Sun Clouds that can be found in the Resources-Materials section on the Corona website. This was added into the scene environment tab in a Corona output material which allows you to make exposure/colour adjustments.
On a side note – if you accidentally press the reset setting tab (which I did) it will get rid of the Corona output material as well, so to make life easier I add a zero at the beginning of the name so that it will turn up at the top of the scene material list and save me from scrolling through every material I made trying to find it.
For the internal lighting I didn't use any IES lights simply because I don't think it added anything to the look I was going for.
In Corona 1.6 there's now a function in the Light mix that allows you to change all your lights in the scene after the render and then paste those settings back into the scene lights once you've made those adjustments using the >Scene button.
The reason you use this scene button to copy the values back into the light settings is because the lightmix is basically faking increase/decrease in light intensity. It takes the existing information it gets from the render and ramps up the intensity as you would if you had the pass separately in Photoshop – which, as you probably know, can create banding, noise, inaccurate reflections etc. But if you transfer the settings once you're happy with them, back to the light settings in the scene and re-render, it will give you a much better, accurate and crisp render.
As you can see in the screen grab above, the lights have an extremely high intensity (I didn't actually notice this until I started writing this breakdown and taking screenshots), which is a result of transferring the lightmix settings onto the light settings.
E.g. my sphere lights were very small and I had to increase them a lot in the light mix until I was happy, copied the values back into my lights and continued without going into the light settings again, hence the very high values.
Finally, for the external outdoor light bulbs and oven lights I applied a Corona light material to the filament geometry with a basic falloff going from white to orange, giving the light a softer glow.
Below is a light breakdown for one of the images so you can see what each light is doing.
I won't go into much detail into the Materials for this project as they are quite basic, but I thought I would include a screenshot of the wood decking of the external shot. I used the Multitexture plug-in by CG Source which, if you have not used it before, I would highly recommend, as it allows you to randomise textures on elements of an object. That was then put into a composite with more dirt layers added on top, plus monochrome versions created for reflections and bump. I also tend to add a coronaAO map on a 20% multiply to most of my materials diffuse colour to help bring out small details of a model.
Depth Of Field
I love depth of field with Corona, it is very intuitive and being able to view it in the interactive render with very little refresh times is a real time saver when trying to work out the intensity you want.
There are a few ways to set it up but I just wanted explain how I'm currently doing it.
To start off I set up my camera and by default the focal point is the point of the camera target. As long as the target is in the correct place when I set it up my shots, this usually works fine and would just need a little bit of adjusting.
Below are some examples of different positions of the target:
You can also put in the distance manually to add DOF at a later stage if you have already locked down your camera angle, but didn't set up the target. An easy way to work it out is to use either the environment or the clipping range in the camera settings: enable either setting and move the planes that appear to the object you want to be in focus.
Then copy and paste the value into the corona DOF override.
Now that we have specified the focus we need to work out the intensity of the blur. You can achieve this by changing the F-stop setting in the Corona camera mod.
Finally we need to determine the shape of the bokeh. If you go to the Corona render settings you can adjust the number of blades in the camera settings. This is basically recreating the mechanical shutter found in camera lenses. Generally, the better the lens, the more blades you get, which results in circular Bokeh - cheaper lenses tend to have more angular bokeh patterns.
The below examples show how a higher number changes the effect. You can also change it to circular or custom map in the drop down menu. Just play around a little with this until you have your desired look.
I did a few test renders of a scene and for 600 passes at 2500 pixels they were taking about 20 hours. I was using a i7 4930k Processor, but with depth of field and lots of displacement these kind of render times were not a surprise to me. I then started to render one camera that was looking through the back sliding doors into the garden area. I left it rendering as I was away for 2 days but when I came back to it, Corona estimated another 255 hours remaining....not good. I spent ages trying to work out why it was taking so long until I realised it was a little box in my glass material that I had forgotten to tick. I thought I would bring this up in case it helps anyone else that is currently banging their head against a wall. Even though I have been using 3DS Max for many years, there's still times that I forget about the simple things....normally a little tick box...
Corona has great post production tools with a big collection of LUT's built in. For these images I used Kim_Amland_Photographic_01. It is also nice to not have to worry about shutter speed and ISO in the camera settings to adjust the exposure, although the CoronaCameraMod does have these options if you want to use them. I found that leaving them on the default settings and using the simple exposure setting in the post processing tab to adjust it worked really well. Below are the tone mapping settings I used:
I found I could get the images to a standard I was happy with by just using the built in tone mapping tools. I did use Photoshop to increase some reflections and translucency but in the end these where very minimal and didn't add a huge deal to the images.
Below is a render from the Corona frame buffer and then the final Photoshopped version.