Background Image

Background Image

Background Images are special images which you can place behind your model.

  • Simple Background - you can use any image as a simple background for skies or other pruposes
  • HDRi Skies - for full illumination and reflection of a background image, you will need to use an HDRi Sky
  • Image Layer WIzard - backgrounds can easily be positioned using the Image Layer Wizard.
  • See: HDRi Skies
  • Video: Background Wizard Video
Use images for background

IRender can place a Background Image behind your model.

Use the Background Tab or the Background Wizard and select an image to use as the background.

Contents

Background Wizard

Background Wizard.jpg

The new Background Wizard , introduced in Version 4.0, make it easy to position your rendered model in a background, and to remember the settings for future renderings.

To invoke the new Background Wizard select Preview/Position from the Background Tab.

Features:

  • Background Positioning - slide or resize background image.
  • Distortion - distort background image to adjust for Perspective or rotations.
  • Save or Copy - save or copy the resultant image directly from the rendering without re-rendering.

Watch the Video: Background Wizard Video



Background Tab

Background 72.png

The Background Tab is used to define background image and also for Ground Plane materials.

Background-tab.jpg


Background Image

  • Click Browse to select an image to use for the background.
  • Click Clear to clear the background image.

Visibility

  • Visible - image is visible (will override any sky settings)
  • Reflected - image is reflected in windows.

Projection

This determines how the image is projected onto the sky of background.
  • Flat
  • Cylindrical
  • Spherical

Create Planar HDRi Image

Converts a normal image to a HDRi background image.
See: Planar HDRi Backgrounds

Clear

Clear out Background Image

Browse

Select HDRi Image from disk

Positioning

Offsets and Scales

Use the Image Layer Wizard to size and position the background image and set these values.

Rotation

for Cylindrical and Spherical Projections.

Maintain Aspect Ratio

if this is not checked, the background image is stretched to fill the screen.

Adjust Center Line to Horizon

If checked then the image will be scaled and offset so that the horizontal center line of the image matches the horizon of the current perspective view.
The image is scaled and positioned so that it still fills the entire background of the rendered image.
See: Horizon

Reset

Resets Offsets, Scales and Rotation.

Preview/Position

Loads the Background Wizard to easily position and scale the background image.
See: Background Image for examples.

Ground Plane

  • On - turns on the Ground Plane
  • Alpha Channel - makes the ground plane transparent, but shows the shadows on the ground.
    See: Alpha Channel
  • Elevation - set the elevation of the ground plane.
  • See: Ground Plane

Ground Plane Material

  • From the Background Tab you can define and edit materials for the Ground Plane.

This lets you apply a grass texture for land, or a Procedural Bump Map and reflection to emulate water.

Alpha Transparent Ground Plane

With an Alpha Transparent Ground Plane, you can save the rendering as an Alpha Transparent image, and the ground plane will be transparent. However, shadows on the ground will be visible. This can be used to place the ground plane image on top of a background image and still see where the shadows would appear. (Of course this works best if you are placing he image on a flat surface.)



Visible and Reflected

This shows samples of the 4 possibilities for Background visible, and Background reflected.

A non-sky image has been used for the background, because it make it easier to wee when it is visible and when it is reflected.

Visible and Reflected background - visible on, reflected on
This is normal, but there may be times when you want to see the background, but not reflect it in windows.
Visible but not Reflected background. - visible on, reflected off
The background is visible - but not reflected in the dome.
Not Visible, butReflected background - visible off, reflected on
This could ne used to reflect dramatic clouds without showing clouds in the sky.
No background image used - visible off, reflected off


Background Projections

These determine how the image is projected onto the sky of background.

Here are some examples using the same sky background and 3 different projections.

Notice that the cylindrical and spherical projections stretch out the image more to fill the entire background. This may work properly with normal sky images, or you may need a 360 degree image to stretch around the cylinder or sphere.


Flat

Image fills render area. See Scales and Offsets below.


Cylindrical

Image wraps around 360 degree cylinder.


Spherical

Image wraps around 360 degree sphere.


Scales and Offsets

Here are some examples of scale and offset for Backgrounds.

0% offset, 100% scale.
50% X offset - 100% scale.
Notice it moves the image 50% to the left and repeats.
0% X offset - 150% scale (X and Y).
50% X offset - 150% scale (X and Y).
The X Offset seems to be effected by the scale.


Horizon

If you check Adjust Center Line to Horizon, then the image will be scaled and offset so that the vertical centerline of the image matches the horizon of the current perspective view. If you have created your background image with the horizon in the center, then this provides a more realistic view - especially when seen through windows.


Background Image with horizon at center of image. (You can place the horizon at the center by enlarging the image in a Paint Program, shifting the image so that the horizon is in the center, and adding additional color above or below the image to complete it.
rendered scene without background image to show the location of the horizon. Not that the horizon is not in the center of the rendered area.
Rendered image with background adjusted to match the horizon.


Planar HDRi backgrounds

Planar HDRi Backgrounds

You can use a, (non panoramic), HDRi image as a background.

Image Adjustments

If you use a Planar HDRi background with the Path Tracer , you can adjust its brightness as an additional lighting channel after rendering. (This is not working with the standard renderer yet)

  • See: [[]]
Converting standard image to HDRi.

You can use a, (non panoramic), HDRi image as a background.

To use this feature, select Browse on the Background tab and choose a .HDR file.

You can create a Planar HDRi from a normal image using the Convert Image to HDRi background button on the Background Setup Tab.

Settings for Inverse Tone Mapping

Tone mapping, (converting from HDRi to normal images), takes luminance and creates RGB colors for display or saving in an image. Inverse tone mapping reverses that equation. nXt's tone operator requires two other pieces of information in order to invert it properly-- the average luminance and the maximum luminance of a scene. The way it works at the moment is that you select Daylight, Nighttime to get default values, and then adjust the custom settings for Average and Maximum illumination in the image.

Lumens and Default Values

After selecting a normal, ("Tone Mapped"), image, you can set the Average Lumens and maximum Lumens which control how bright the image will appear.

  • Daylight 5,000 and 20,000
  • Nighttime 1 and 500

Load this image as a Planar HDRi Background

After converting your image, you can load it as a HDRi background for rendering.
Image Adjustments

Adjusting Background image in the nXt Image Editor

If you use a Planar HDRi background with the Path Tracer , you can adjust its brightness as an additional lighting channel after rendering.

HDRi Image Adjustment are not working with the standard renderer yet from the Rendering Window. However, you can save the rendered image in Native Image format and use the HDRi background channel (8) in the nXt Image Editor .

See also