This page provides details to using the post rendering tools for adjusting image colors and contrast.

 

Page Contents

 

Overview


The V-Ray frame buffer allows various color corrections to be applied to the image. Some of the corrections are applied only when the image is displayed on the screen but are not applied when it is saved to disk. Corrections that are not applied for disk images are those that are only required to display the image - i.e. sRGB, LUT, OCIO, ICC color corrections.  Corrections are generally applied as they are listed in the color corrections window from top to bottom - i.e. exposure is applied first and display color corrections like LUT, OCIO and ICC are applied last.

You can turn on and off a particular color correction using the check box to the left of its name. You can expand and hide the parameters for a particular color correction using the button. Clicking on the button displays a short menu that allows you to reset the parameters for the particular color correction to their default values, and to save and load just the parameters for that color correction.

All color corrections done in the V-Ray frame buffer are saved within the Rhino project file.

The Color Corrections panel can be docked or undocked from the VFB by right-clicking the Show corrections control button.

Global Presets


You can save the entire state of the color corrections window to a file for later reuse. Clicking on the Global... button shows a menu that allows you to save and load the current state.

 


 

Exposure


This color correction allows you to apply exposure and contrast to the image. Exposure of 0.0 leaves the original image brightness, +1.0 makes it twice as bright, -1.0 makes it twice as dark, and so on. Highlight Burn  allows you to selectively apply exposure corrections to highlights in the image.  Positive Contrast values push the colors away from the medium gray value to increase image contrast, while negative values push the colors closer to medium grey.

 

White Balance


The white balance allows you to correct the colors in the image so that objects that are white appear white in the final image.


 

 

Hue/Saturation


This correction allows you to apply HSL transformation on the image colors. Moving the Hue slider changes the overall hue of the image colors (grey colors remain intact). Lower Saturation values move the image towards greyscale while higher values increase the colors. Higher Lightness values add white to the image, whereas lower values subtract white from the image.

 

Color Balance


This correction allows you to adjust the overall color tone of the image, as well as the tone of the dark (shadow), medium, and bright (highlight) colors. The color corrections are additive in that the All correction affects all colors of the image, and the Shadows/Midtones/Highlights corrections adjust the individual components on top of the All correction.

 

Levels


This correction shows a histogram of the image colors and allows you to remap them. The buttons allow you to view the distribution of the individual color components only, and the turns on all three components.

 

Move the two slider nodes below the histogram to remap the image colors. Ctrl+left click below the gradient between two sliders to add a new slider between them. Shift+click on a slider to delete it.


 

 

 

Curve


 This correction allows you to remap the image colors with a Bezier curve. The control also allows you to save and load .acv curve files from Adobe Photoshop.


 

 

Controlling the View  

Use the mouse wheel to zoom in and out of the curve view. Drag with the middle mouse button to pan.

Controlling the Bezier Points

Click on a point to select it. Draw a rectangle to select multiple points at once. Click and drag on a selected point or its tangents to move them. To add a new point, Ctrl+click on the curve. To delete points, select them and press Del, or alternatively Shift+click on a point. Once a point is selected, you can also use the input coordinates field in the upper left to modify its position.

Right-click on a point to bring up a context menu with additional options for that point:


 

 

Context Menu

Right-clicking in the curve view brings up a context menu with additional options:


 


The following menu items are available:

Menu item   Description
Zoom allAdjust the curve view so that all points are visible
Undo/RedoUndo and redo modifications to the curve
LoadLoad the curve control from a file. Two formats are available: native .bcurve and PhotoShop .acv.
SaveSave the curve control to a file. Two formats are available: native .bcurve and PhotoShop .acv
ResetReset the curve control to its default state.
Select internal onlySelect only the points which are currently visible in the curve view.
Select allSelect all points.
Snap to gridToggle snapping to the curve grid. When enabled, moving points snaps them to the grid nodes.

When working with .acv files, some approximations are performed, as the curves in the .acv files are described by a different mathematical formula

 

Background Image


This section allows you to load an image and use it as a background for your rendering.


 

 

Load – Click to load a file that is going to be used as a background.

Clear – Clears the loaded file.

As foreground – When enabled, the image loaded in the field above will be used as a foreground. This means that the image will be on top of the rendering and you will be able to see the rendering only if the image has an alpha channel.

 

LUT


This correction allows you to remap the image colors based on an IRIDAS .cube LUT (Look-Up Table) file. This is a display correction that is only applied when the image is viewed in the frame buffer. It is not applied when the image is saved to a file.


 

 

This correction can be controlled with environment variables. Settings VRAY_VFB_LUT=1 automatically turns on the LUT correction by default. A LUT file can be specified with the VRAY_VFB_LUT_FILE environment variable.

 

OpenColorIO (OCIO)


This correction allows you to apply display color corrections from an .ocio color profile to the image colors. When this correction is enabled and no specific .ocio profile is specified, it will attempt to read the OCIO environment variable and apply the profile specified in it. This is a display correction that is only applied when the image is viewed in the frame buffer. It is not applied when the image is saved to a file.


 


Input color space – Allows you to choose the input color space for the image; normally this is a linear color space as V-Ray internally works in that space.

Display device – Allows you to choose the device on which the VFB with the image is displayed.

View transform – Allows you to specify the viewing transformation.

 

ICC


This correction allows you to apply an ICC profile to the image so that it matches (i.e. the appearance of the image in Adobe Photoshop). This is a display correction that is only applied when the image is viewed in the frame buffer. It is not applied when the image is saved to a file.


 

 

This correction can be controlled with environment variables. Setting the VRAY_VFB_ICC_FILE allows to automatically specify an ICC profile.