Why Does Blender's Depth or Object-ID Pass Ignore Part of My Transparent Product?

Separate visible appearance from data-pass selection

A transparent product cover can be visibly present in the Combined render while a downstream depth effect behaves as though it were absent. This is possible because a Combined image and a data pass serve different purposes.

Blender's Cycles documentation states that Alpha Threshold affects Depth, Position, Normal, Vector, UV and Index passes. A surface must meet the configured opacity threshold to contribute to those passes. If it does not, the renderer can continue to a surface behind it.

At Alpha Threshold 0.0, the first surface hit writes to these passes regardless of opacity. Raising the threshold can skip mostly transparent surfaces until a sufficiently opaque one is encountered.

This behavior should not be generalized to every render pass or to all render engines. Confirm that the actual pass is among those documented and that the scene is using the relevant Cycles configuration.

Compare two thresholds without changing the material

Keep the product geometry, camera, lighting and material unchanged. Enable the data pass required by the compositing operation and inspect the Alpha Threshold setting.

Prepare a comparison using threshold 0.0 and a higher value appropriate to the hypothetical test. Inspect the same image region in the Combined render and the selected data pass. If the Combined appearance stays consistent while the data pass changes which surface it records, the threshold is a plausible cause.

Do not interpret a depth value as a transparency measurement. A depth pass records a selected surface's distance, not the complete sequence of transparent surfaces and their optical contributions.

Similarly, an Object Index pass can identify a selected surface according to its data-pass rules, but it is not automatically an anti-aliased, transparency-aware product cutout. Blender documents that certain depth and index passes are not anti-aliased.

Hypothetical clear display cover

Hypothetical illustration—not an executed Blender render: a product display contains a translucent front cover with an illustrative opacity of 0.25 and an opaque housing behind it.

The editor needs a depth-based compositing treatment associated with the front cover. At Alpha Threshold 0.0, the documented rule selects the first encountered surface. At a hypothetical threshold of 0.5, the 0.25-opacity front cover does not meet the threshold, so the pass can record a sufficiently opaque surface behind it.

The Combined image may still show the front cover. This is a data-selection difference, not proof that the material disappeared.

The numerical opacity is a teaching fixture; real material and render settings must be inspected rather than inferred from a screenshot.

Select the pass according to the intended effect

Determine whether the compositor needs the front cover's geometric depth, the opaque housing's depth or a mask representing the complete visible transparent material. These are different information requirements.

Choose and document the Alpha Threshold that supports the intended data interpretation, then inspect the resulting composite. A lower threshold is not universally better: it may select a transparent surface that another effect intentionally needs to ignore.

Keep the Combined render as a separate visual reference. The existing mesh-cutout guide concerns missing holes in an edited product photograph. This guide concerns Blender's documented data-pass opacity threshold even when the rendered product geometry is correct.

Record your own observations

The filled rows are illustrative examples. Use the blank row for your own files and observations.

Download the editable CSV worksheet

What the references establish

• Blender 5.0 Manual — Passes: Directly documents Alpha Threshold, the affected Cycles data passes, first-surface behavior at zero and skipping mostly transparent surfaces at higher values.