Grading your Renders
The holy grail of pretty well any CGI endeavour is realism. We all want those who view our work to believe on some level that it is real. CGI is notoriously perfect, and great effort is made to try and minimise the perfection that CGI brings. Much can be attained in terms of texturing and taking away the geometric perfection. One area however that sits uncomfortably in the middle is automotive rendering. Now of course you could create an old and battered vehicle, and texture it accordingly. Usually however, cars are rendered to be uncompromisingly beautiful. It is after all where the term ‘Car Porn’ comes from.
This then leaves the post processing or grading to attempt to add realism. This realism is added closer to the viewer. It is not the subject or it’s geometry, but the CAMERA.
Step 1 : Starting Point
For this tutorial I am using my Lotus Exige model, created with Lightwave 3D, and rendered in this instance with Hypershot HD (now known as Keyshot). It’s a pretty nice render over all, but it does seem to clinical and dead.
Step 2 : Optical Imperfection
The first step is one of the most important. Camera lenses will generally suffer from Chromatic Aberrations. This is where the light colours separate slightly quite distinctly, as it does when passed through a glass prism. Photoshop includes a filter called Lens Correction, which amongst other things includes sliders to remove colour fringing caused by Chromatic Aberration. We are doing the opposite, and we use the sliders to fake the effect. To some degree it will be trial and error to get the level and look of effect you want.
Step 3 : Boost your Highlights
Duplicate the background layer, and apply a Gaussian Blur to it. I find that 5-10px works best, but as with most things, you need to experiment to find your desired look. Typically you need to stay in the mid ground between the finished effect for this layer looking harsh, or to dreamy and ethereal.
Step 4 : Colour Dodge
Now set the layer mode to Colour Dodge, and the opacity to 35%. This will have the effect of brightening the render, but more importantly, slightly burning out the really bright highlights. The blur we added previously help soften and bloom the effect just a little.
Step 5 : Bring the Noise
Now add a new layer via the Layer menu, and set the layer mode to Multiply. Also make sure yo tick the box to specify that the layer will be filled with a multiply neutral colour. We need this ticked because noise cannot be applied to an empty layer, and the neutral colour will be invisible (neutral white in this case).
Step 6 : Add and Adjust
Apply the Noise Filter with a value of 4% Gaussian Monochromatic. This is my preferred setting, but you can experiment with different values. These settings for me seem quite subtle, but some people seem far less keen on noise being added. The advantage of adding it in a separate layer is that you can use the layer opacity to fine tune the visibility of the noise.
Step 7 : Colour Tint
Now add a Solid Colour adjustment layer, selecting your tint colour, and setting the layer mode to Colour. An opacity of around 30% avoids overpowering the colours, but each render can vary of course.
Adding a tint to the render really transforms it. As with aberrations, it removes the perfect colours which our eye might not expect to see through a camera. It also affords you a chance to change the mood of your render by cooling it down or warming it up. I typically favour a slight green tint, almost as you’d get from some fluorescent lighting, however a warmer orange can enhance the lighting of the sun. My example with the Exige can be greatly varied in this way.
Step 8 : Vignette
Now add a new layer via the layers menu, and select the mode as Overlay, and as we did with the noise layer, tick the box to have the layer filled with an overlay neutral colour. This will allow us to fine tune the strength of our vignette.
Step 9 : Lens Correction Again
Apply the Lens Correction filter, ignoring all settings other than setting the Vignette Amount to -100% and leaving the Centre value alone, as we don’t want the vignette to be off centre.
Step 10 : Almost Done!
I like to do wide screen renders, and you can create a much more cinematic effect by making your canvas standard HDTV resolution, in this case 1920×1080. This has the effect of giving us the familiar letterbox black bars, emphasising the wide aspect ratio of the render.
The Finished & Graded Render
The completed render, looking just that little bit more convincing than the straight render. Of course what we are doing is exaggerating somewhat the optical deficiencies of our camera so as to make them a little more obvious, in much the same way that often small details such as panel shut lines on large ships need to be slight bigger than they would be in reality, to make sure the viewer sees them.