This page provides information on the color corrections tools found in the V-Ray Frame Buffer.


Page Contents



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, and are not burned within the image when saving it to disk - i.e. sRGB, LUT, OCIO, ICC. 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 for resetting the parameters for the particular color correction to their default values, and for saving and loading just the parameters for that color correction.

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




UI Path: ||V-Ray VFB tab|| > VFB Toolbar > 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 presets... button shows a menu for saving and loading the current settings.



This color correction applies exposure and contrast to the image.



Exposure – Adjusts the amount of light taken into the camera. A value 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 – Selectively applies exposure corrections to highlights in the image.

Contrast – Adjusts the difference between pixel values. Positive numbers push the colors away from the medium gray value to increase image contrast, while negative values push the colors closer to medium grey, which makes the color difference more similar to each other.


White Balance

The white balance setting corrects the colors in the image so that objects that are white appear white in the final image.



The value in this field is Kelvin temperature. It shifts the white point for the pixels in the rendered image. 



This correction applies HSL transformation on the image colors.



Hue – Changes the overall color values of the image (grey colors remain intact).

Saturation – Adjusts the amount of color apart of each pixel. Negative values move the image towards greyscale while positive values increase the vibrance of the colors.

Lightness – Adds white to the pixels with positive values, while negative values add black to the pixels in the image.


Color Balance

This correction adjusts 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.



This correction shows a histogram of the image colors that can be remapped. The       buttons show the distribution of the individual color components only, and the   button 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.



This correction remaps the image colors with a Bezier curve. The control also saves and loads .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, 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 itemDescription
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.


Note: Some approximations are performed on .acv files, as the curves in the .acv files are described by a different mathematical formula.


Background Image

This section loads an image and uses it as a background for your rendering.



Load – Loads a file 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.



This correction remaps 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.


OpenColorO (OCIO)  

This correction applies 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  – Specifies the input color space for the image; normally this is a linear color space as V-Ray internally works in that space.

Display device – Specifies the device on which the VFB with the image is displayed.

View transform – Specifies the viewing transformation.



This correction applies 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 variable specifies an ICC profile.