Corona Bitmap

This page provides information on the Corona Bitmap loader, its settings and usage.

Overview

Corona can load bitmap textures using two supported nodes in the material editor:

Corona Bitmap
3ds Max native Bitmap

Both of them produce almost identical results, however there are some advantages of using the Corona Bitmap over the 3ds Max Bitmap node:

Corona Bitmaps render faster.
Corona Bitmaps use less RAM thanks to the out-of-core Rendering feature.
Corona Bitmap has a simplified UI and controls and additional options for texture mapping and tiling.
Additional “Dome” mapping lets you have ground projected environment maps, with controls on placement, size, and camera position.
Environment maps can be transformed using a scene node.
Additional tiling mode "Clamp" continues the pixels at the edges of the texture.

Right-click anywhere in the viewport and select Corona Converter:
Use one of the buttons - Bitmap(s) → CoronaBitmap(s) or CoronaBitmap(s) → Bitmap(s):

You can learn more about the Corona Converter here.

Settings

UVW Mapping

Use Real-World Scale – When turned on, applies the map to objects using the real-world Width and Height values instead of UV values.

Map Channel – Allows to specify a map channel.

Offset (U;V) – Controls a horizontal/vertical offset.

Tiling (U;V) – Controls a horizontal/vertical tiling.

Tiling Mode:

No Tiling – For UV coordinates outside of [0,1] range the bitmap returns black color.
Repeat Tiling – The bitmap is periodically repeated outside of [0,1] range (i.e. for UV coordinates u = 0, v = 1.2 it will have the same value as u = 0, v = 0.2).
Mirrored Tiling – The bitmap is periodically repeated, but each odd repetition is mirrored (i.e. for UV coordinates u = 0, v = 1.2 it will have the same value as u = 0, v = 0.8). This means the repetition is seamless.
Clamp – For UV coordinates outside of [0,1] range the bitmap has the value of the closest valid pixel in the range (i.e. for UV coordinates u = 0, v = 5 it will have value of u = 0, v = 1). Often called "clamping".

Lock Icon – Lock the set width (U) and height (V) ratio.

Fit To Bitmap – Sets the height according to the aspect ration of loaded bitmap.

W Rotation [deg] – Rotates the map in Z axis.

Environment mapping

Mode:

Spherical – Most common format of environment bitmaps, bitmap pixel coordinates correspond to spherical coordinates.
Screen – Tries to map bitmap in such a way that it is mapped parallel to the camera sensor.
Dome – Similar to spherical, but the sphere is not infinite, it has a given center and size.
Cross – Common format from computer games - bitmap stores environment as unfolded cube.
Mirror Ball – Mapping computed from rays reflecting from perfect mirror sphere (quite uncommon, but it was requested by the users).

Rotation [deg] – Rotates the map in X axis.

Transform from object – If used, the bitmap rotation in the environment slot (and dome origin, if dome mapping is used) is controlled by transform from a selected scene object. The other bitmap rotations are still applied on top of this.

Rotation in any axis can be used, so this can be used to tilt maps.

Dome Mode

Origin X/Y/Z – Sets the centerpoint of the virtual dome in the scene, using the units specified in 3ds Max.

Radius – Sets the size of the virtual dome, using the units specified in 3ds Max. The value should be at least a bit larger than the scene size, or unexpected results may occur. A good practice is to use a value similar to the scale of the environment in the image.

Camera height – Controls how much of the image is on the "floor" of the virtual dome, and how much is on the dome itself. If you know the height of the camera when the image was taken, use that value. If you do not know the height of the camera, adjust this by eye to minimize distortion on the floor of the dome.

Crop/Place

On – Makes crop/place active.

Crop – Makes Crop active.

Place – Makes Place active.

View Image – Opens a window that shows the bitmap surrounded by a region outline with handles at its sides and corners

U/V – Crops/Places the bitmap by UV coordinates.

Width/Height – Crops/Places the bitmap by width/height values.

Channel Outputs

Alpha – When map is used together with constant color, alpha determines how they are mixed (alpha = 1 - only map is used, alpha = 0 only color is used.). Here the user can select how is the alpha computed:

None (Opaque) – Alpha is always 1.
RGB Intensity – Alpha is computed from RGB color.
Image Alpha – Alpha is taken from image (if present, e.g. in TGA/PNG) or set to 1 if missing.

Mono – When the output of map is supposed to be a single channel (e.g. for material roughness), this is how we compute it.

RGB Intensity – Computed from RGB color.
Image Alpha – Single channel is taken from image (if present, e.g. in TGA/PNG) or set to 1 if missing.

RGB – Actual color output when map is used for color inputs (e.g. diffuse color in material).

RGB – Actual color stored in bitmap.
ImageAlphaasgray – Gray color is computed from alpha stored in the image.

Color Space

Selects the color space of the input texture. The texture values are transformed from the selected space to the space in which the material tree is evaluated. It is a Linear sRGB with the Gamma workflow or current rendering space with the OCIO workflow.

RGB Primaries:

Linear sRGB – Classic color space with a limited gamut.
ACEScg – ACES linear color space with AP1 primaries, it was designed for computer graphics operations.
Raw – the pixel values are used without any transformations, it is intended, for example, for normal maps.
Auto – One of the three spaces above is selected based on the file name(e.g. ''_acescg'' suffix leads to selection of the ACEScg option). In OCIO workflow, the rules are defined in the config file.

Bitmap

Load Map – Selects the bitmap using the standard file browser.

Reload – Reloads the bitmap file using the same name and path. You don’t need to use the file browser to reload the bitmap after you've updated it in your paint program. Clicking reload for any instance of the map updates the map in all sample slots and in the scene.

Filtering

Blur – Controls the blurriness of the image.

Interpolation – Determines how we compute a color for a given UV coordinates from the bitmap. The bitmap is discrete - e.g. pixel has constant color, but pixel has an area and UV coordinates tells us we want color from a given point. The color from such a point is computed from surrounding pixels.

Bilinear (faster) – Finds four closest pixels to the UV coordinate and mix their color depending on how close they are to the UV coordinate.
Bicubic (smoother) – Similar to bilinear, but includes even more pixels in the color computation.
Nearest Neighbour (low quality, faster) – It just finds pixel closest to the UV coordinate and returns the color.