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exrtrader2018:available_buffers

Notes about Buffers

LightWave 2018 comes with a massive change in buffer management. Previously, there was a fixed set of buffers. as of LightWave 2018, the amount of buffers can vary since both materials as well as the user can add buffers if needed.

exrTrader 2018 will build a list of available buffer on the fly. It also tries to name the corresponding OpenEXR layers and channels as smartly as possible. Both the layer names and channel names can be changed at any time.

Please refer to the LightWave documentation for a full list of buffers supplied by LightWave.

Some buffers will get special treatment by exrTrader 2018:

Buffer NameDescriptionChannels 1)
Final RenderThis buffer contains the final, rendered image. This is identical to the image save by using the LightWave 3D render globals.RGBA
SpecialThe special buffer is quite … “special” indeed 2) .
In the surface editor, under the Advanced tab, there is a button to edit the Special Buffers. LightWave 3D provides 4 of them. These are applied on a surface by surface basis.
A value of 0.0 in a special buffer is equivalent to black, 1.0 is white (values can go beyond those limit as they are stored in float/HDR buffers).
The tricky bit is the fact that image filters can only read one of these special buffers. Which one depends on the location of the image filter plugin in the list of applied image filters in the Processing tab of the Effects panel in LightWave 3D.
The first image filter in the list will only be able to read special buffer #1, the second image filter can only read special buffer #2, the third one bufer #3 and the fourth one only buffer #4. All image filters beyond that only have access to special buffer #4.
Practically this means that exrTrader will need to be applied four times as an image filter to the list to be able to access all four special buffers. In this case we'd recommend using the first instance of exrTrader in the list to save all the other buffers as well, and only use the slots 2-4 to save the special buffers – to separate image files.
Please note, given the AOVs in LightWave 2018, this buffer is obsolete nowadays.
Y
DepthThis buffer stores the distance of a surface from the camera.
Due to the fact that the depth is stored as a proper float image and the pixels represent the distance to the camera in metres, there's a few facts to remember.
The first image to the right shows the normalized depth buffer for the sample render. There isn't much to see because the top of the image is the backdrop. In LightWave the backdrop is always rendered at an infinite distance 3).
A normalized view looks at the highest and the lowest value in an image and then tries to display anything between them in the visible range from 0.0 to 1.0. In this case the backdrop compressed to be at 1.0, and all other values are compressed respectively. This means that the actual items are relatively close to the camera (at least in relation to the backdrop) and thus displayed as being black (which corresponds of a distance of 0, or something very close to it).
If you intend to composite in an application that handles float images (and the tools that are used to actually work with a float depth buffer) then there should be no need to change anything.
If you intend to save the depth buffer as a low dynamic range image then you can use the Minimum and Maximum settings to define a range which should be normalized into the visible range.
Y
MotionThis buffer stores the motion of a pixel during the current frame in screen space. The motion is encoded in the R and B channel.
Since LightWave 3D creates float channels, the values represent the movement in pixels. This implies that the values may actually be negative as well, depending on the direction of movement.
If the compositing package can deal with floating point motion buffers this is the best way to export them.
Some plugins require the motion vectors to be normalized into values from 0.0 to 1.0, where 0.5 is equivalent to no motion at all.
The Offset and Scale processing options allow you to change the motion buffer to be acceptable by such plugins 4) - as a downside one needs to estimate how far the any of the pixels actually travel (in pixels) – or use an arbitrary value, such as the largest dimension of the image in pixels.
As an example, using 1920 as the largest distance an pixel could travel:
The Offset would need to be 1920 - to basically push the negative values into the positive range.
The Scale would need to be 1 / (1920 * 2) (roughly 0.00026) – to compress the values into a range from 0 to 1.0.
XY
Surface IDThis buffers contains a unique number for every surface in the scene.
To get a better view on the values stored in this buffer you should normalize the preview.
ID
Object IDThis buffers contains a unique number for every object in the scene.
To get a better view on the values stored in this buffer you should normalize the preview.
ID
1)
RGBA are four float channels, RGB/XYZ three, XY/UV two, Y is one float channel.
I is a single luminance channel
2)
Yes, sorry, I couldn't resist.
3)
Well, not really infinite… but very, very, very far away,
4)
However, you may be able to edit it in your compositing package prior to sending it to those plugins as well. This would be a little less dangerous and more flexible.
exrtrader2018/available_buffers.txt · Last modified: 2017/12/27 10:38 by lightwolf