FAQ/Viewing Z Channels

From VFXPedia

When you view an image with Z depth information in Fusion (using the Z channel in the image view's Channel menu), it may look completely black or completely white (or perhaps black and white), rather than a smooth grey scale to indicate depth. This can happen when viewing a depth channel from a new source, as different renderers often produce very different ranges of depth values.

Firstly, the depth values in the image are probably fine. You can verify this with the Color Inspector subview, or with the Z values displayed on the bottom status bar when moving the pointer over your image.

However, your image view is likely set up to expect a different range of Z values than what you are using, so you're not seeing a full black-to-white range. Normalising the view (with the view's context menu or toolbar button) scans the image to determine the nearest and furthest values and adjusts the view to show a full black-to-white range, but does not change the Z values within the image itself. Fusion's Depth tools will work fine with or without view normalisation, as they can be set to work with any depth range. You generally do not need to change the Z channel in any way.

For easier visualisation, you can change the range of depth values that the image view expects. Look in Prefs/View, select a view from the dropdown list, and change the Far and Near values to more closely encompass the range of depths in your shot. You should now get a more useful view of your Z depth, with a range of grey pixels - but again, this is not needed for the Depth tools to function correctly.

Normalising the Z values within the image itself (using the AutoGain tool with Do Z turned on) is a Bad Idea. If the range of Z values in your shot changes, then AutoGain will affect the Z values differently every frame (giving a fixed object a different depth in each frame), and this can cause flickering or other inaccuracies from tools that use the Z channel. It is sometimes possible to copy Z values into the RGB channels with a Channel Boolean tool to allow tweaking, but this can result in loss of range or accuracy, especially if an integer pixel format is being used.