Investigation: Transformations Change the Evidence

A computer-vision pipeline often transforms an image before producing a result. A transformation can make a feature easier to measure, but it can also remove information or expose a fragile shortcut.

From framework operation to vision evidence

A framework may place a tensor on a device, run declared operations, and track a computational graph. Those conveniences do not decide whether the input represents the intended scene. A perfectly executed operation on a cropped or poorly lit image still processes incomplete or changed evidence.

Resize changes grid dimensions. Grayscale combines color channels. Thresholding separates values using a cutoff. Edge detection marks locations where neighboring values differ enough.

if neighbor_difference >= threshold:
    edge = 1
else:
    edge = 0

An edge is evidence of a sharp numeric change. It is not an object name.

Controlled comparison

Suppose the supplied normal scene produces 12 marked edge pixels at threshold 90 and the dim scene produces 8. The physical object did not lose four edges. The capture condition changed stored values, which changed the transform.

If you also lower the threshold, two conditions changed. You can no longer isolate which change explains the result. Hold the transform fixed while changing the scene—or hold the scene fixed while changing one transform setting.

Completed comparison

1. Question: Does dim lighting change the supplied edge evidence?
2. Hold fixed: 6 × 6 grid, grayscale representation, edge rule, threshold 90.
3. Change one condition: normal scene to dim scene.
4. Measure: normal 12/36; dim 8/36.
5. Difference: 8 - 12 = -4 marked pixels.
6. Bounded claim: Under the supplied grids and fixed threshold, dim light produced four fewer marked locations. This does not establish how another camera, image, or model behaves.

Investigation

1. Predict which supplied condition—normal, dim, or cropped—will produce the highest edge count at threshold 90.
2. Predict whether raising the normal-scene threshold from 90 to 120 will mark more or fewer locations.
3. Name the independent variable, measurement, and fixed conditions for each comparison.
4. Preserve both predictions. A failed prediction becomes evidence when the measurement explains the defect.
5. Write one sentence that uses “edge evidence” without saying “object detected.”

Success means another student can repeat the comparison from your declared settings.