Vray Tips: How to Improve Rendering in Vray Frame Buffer

Default Render Output
Original Render Output

Proper scene exposure is a problem most beginners encounter in Vray. Back when I started learning Vray, my workflow was long and tedious. I did all my exposure corrections manually. If I have an underexposed image, I make changes to the physical camera parameters. I render the scene again and examine the output for proper exposure. It always took me several tries before I get the appropriate exposure.

I've always relied on post-processing to improve the dynamic range of my rendering. Wide dynamic range scenes happen when there is a wide gap between the dark and light areas of a scene, usually in interior scenes, when the outside is visible from the inside. Interior scenes facing windows or sliding doors exposed to sunlight are the typical wide dynamic range scenes.

The narrow dynamic range is the problem with the default Vray rendering settings. The range of the dark and light areas is too limited. Vray clips the highlights and the blacks when there's a massive difference between the two.

My workaround for this problem before was to apply exposure bracketing, which will transform my rendering into a high dynamic range rendering. My previous workflow to expand the dynamic range was to make a proper exposure in the dark areas, resulting in overexposed areas on the highlights. Then I'm going to make a separate scene based on the bright spots. This second scene will retrieve all the details from the previous overexposed scene. I combine the two scenes in Photoshop to create a balanced high dynamic range scene.

Vray provides a great tool to address both problems, allowing the correction and bracketing of exposure post rendering. It reduces rendering time and improves workflow within Vray. User can make adjustments after the rendering. It's a powerful post-processing tool that can enhance the output without the need to render the scene again. Vray frame buffer also has lens effects that allow users to improve the scene by adding effects.

Correction Controls

Correction Controls are the tools you will need to adjust the scene after rendering. To activate this tool, click on the first icon on the bottom right corner of the Vray Frame Buffer.

Exposure Controls

The exposure control allows the user to adjust the under-or over-exposed scene. Users can adjust exposure without the need to render the scene again. The default settings for the exposure value are zero.

Sliding the exposure to the right will brighten the scene. Moving the slider to the left will darken it. This tool is handy if the exposure is the only problem on the scene.

Level Controls

Levels control the exposure range of a scene. It can widen the range between the highlights and the blacks, widening the dynamic range. The graph in the level correction tool is the histogram of the scene, and the dark areas are the left-most side of the histogram, while the light spot is the right-most. The red, green, and blue graphs represent the exposure of each channel on the scene.

The default value for blacks is zero, while the default value for highlights is a positive one. These two sliders define the absolute black and white areas of the scene. In the histogram below, the initial position of the highlights slider is close to the dark slider. The graph extends further to the right after the highlight slider. Everything located on the right side after the highlight slider is white. Users can't see these details in the rendering. A blue graph in the farthest right corner of the histogram below needs recovery of details.

To expand your scene's dynamic range, all you need to do is slide the highlight slider to the right. Slide it until it reaches the lightest part of the histogram. After this change, you will notice that your scene is going to be darker. As a result of the widening of the dynamic range, the midrange areas have darkened. To recover the midrange exposure of the scene, we will explore the curve correction of Vray.

Curve Controls

The curves like the levels adjust the blacks and the highlights of the scene. One thing that sets the curves apart from the level is that they can adjust the midrange of the scene's exposure. 

The curve is a graphic representation of the scene's exposure. The default curve correction is a diagonal line. A line from the lower-left corner to the upper right corner of the graph. The lower left-hand corner represents the dark areas of the scene. The upper right corner depicts the light areas of the scene.

Clicking the lower-left corner node will make a second node appear. Moving up this second node will brighten up the dark areas of the scene. It's going to bend the curve upwards towards the upper node. Moving down the second node will darken the darker areas. The higher the curves upward, the brighter the scene becomes.

Clicking the upper right-hand node of the curve will make a second node appear. Moving the upper second node will adjust the lighter parts of the scene. Like the lower second node, moving the upper second node up will brighten the light areas. Pushing it down will darken the light areas.

You can also add a node to the curve to add more control points to the curve. Whenever I adjust the curve, I always try to create an S curve to balance the scene's exposure. The S curve widens the midrange of the scene, making the scene exposure more even.

White Balance Control

The white balance adjusts the temperature of the color of your scene. It's going to change the mood of your scene from cool to warm. Use this tool to change the color temperature of the scene. Sliding the slider to the right will make your scene warmer while sliding it to the left will make it look cooler.

Lens Effect

Users can activate the lens effect by clicking the bottom right-most icon on the Vray Frame buffer.

Bloom/Glare Effect Controls

Bloom is the halo or blur around a light source. Glare is a star-like projection around a light source. Moving the bloom slider to the right eliminates the glare. Moving it to the left removes the glare.

Final Edited Render Output

Comparing the edited output to the original output will notice a lot more detail on the highlight areas. Simple adjustments made earlier have given more information in the rendering. We made exaggerated adjustments made in this tutorial to emphasize the effects of these settings. It is essential to know the basic functions of these settings to achieve the desired output.

Credits to the following:
Sketchup  Modeled by ROS 
Designed by Mies van der Rohe for the 1931 Berlin Building Exposition.
Vray Version 4.20.01

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