BoundingBox

Blackmagic describes Krokodove Bounding Box as a tool that draws a rectangle from a selected channel, with Threshold controls determining the rectangle size. Treat it as channel analysis plus rectangle generation, not as AI detection, Crop or a manually drawn Rectangle mask.

The main Input is a normal 2D RGBA image. BoundingBox analyzes that stream and returns a new image/RGBA result containing the generated rectangular area; the source pixels are not simply passed through as the output.

Channel selects the signal used to find occupied content. The bundled dropdown capture confirms Red, Green, Blue, Alpha and Luminance. The selected channel can radically change the bounds.

Alpha is usually the clearest starting point for isolated transparent graphics. Luminance measures visible brightness instead, so it can behave very differently on opaque dark backgrounds or bright RGB content with partial transparency.

Red, Green and Blue are useful for technical maps and channel-coded sources. On ordinary footage they may produce surprising bounds because background color and noise can become part of the selected signal.

Threshold defines how strong a selected-channel value must be before it contributes to the rectangle. A very low threshold can allow weak noise, glow, premultiplied fringe or a single stray pixel to expand the bounds dramatically.

A threshold that is too high can remove a soft edge, shadow or dim subject region that should have counted as occupied. Tune it on the actual chosen channel and inspect multiple frames rather than copying one number as a preset.

Lock exposes three captured menu choices: All Sides, Vert./Horiz. and None. The labels are verified by the bundled UI capture, while exact pixel-level behavior and animated edge semantics should be live-checked on the target Resolve 21/21.1 build before production presets are published.

Use Lock as a controlled A/B variable rather than assuming it is a universal anti-flicker switch. If bounds jump over time, source-matte stability and Threshold should be checked first.

Extend adds working margin around the detected area. It is most useful after detection is already correct, for example before blur, glow or another downstream utility operation that should not touch the subject edge tightly.

Extend does not repair poor detection. If one remote noise pixel already enlarges the box, padding only enlarges the mistake further.

Color controls the generated rectangle appearance. The expanded captured control shows Red, Green, Blue and Alpha, each at 1.0 in the illustrated state.

Output RGB and the analyzed source Channel are independent stages. You can analyze Luminance and still generate an opaque white rectangle, or analyze Alpha and generate a tinted semi-transparent diagnostic plate.

Output Alpha controls transparency of the generated rectangle. It is not the same as selecting source Alpha for detection and should be inspected independently in the Alpha Viewer when the result is used as a technical matte.

An optional Effect Mask remains a spatial operation gate rather than a replacement for the primary Input or the Channel selector. Feeding a mask there is conceptually different from analyzing that mask as the main source image.

BoundingBox is often most useful as a utility stage: detect occupied area, generate a rectangular plate, then optionally convert that image to a true mask with Bitmap before sending it into a blue Effect Mask socket downstream.

Do not confuse BoundingBox with Crop. Crop changes image-domain boundaries; BoundingBox generates a rectangle based on channel analysis. Use a dedicated Crop or domain tool when the goal is to change canvas boundaries.

Do not confuse it with Rectangle Mask either. Rectangle is user-drawn geometry; BoundingBox derives geometry from image data and therefore can change as the source changes.

Soft mattes, glow, motion blur and shadows can legitimately enlarge the detected region when the selected Channel and Threshold still consider those pixels active. That is source-data behavior, not necessarily a bug.

For temporal work, validate several frames and playback. A box that is perfect on one still can chatter when noise or soft-edge values move around Threshold.

The three bundled captures are the UI anchors for this article: full Controls, the Channel menu and the Lock menu. They verify current labels while hidden Settings fields, exact Lock math and Effect Mask application order remain live-verification items.

For clean diagnosis, start with a synthetic Background constrained by a Rectangle mask, then feed that image into BoundingBox. This isolates Channel, Threshold and Extend behavior from footage noise.