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Media Documentation

ImageUtils

Utility functions for image preprocessing, cropping, scaling, face extraction, and visualization.

centerCrop(bitmap, imageSize): Bitmap

Crops the input bitmap to a centered square and resizes it.

Behavior:

  • If width ≥ height: crops horizontally centered region
  • If height > width: crops vertically centered region
  • Resizes result to (imageSize, imageSize)

Output:

  • Square bitmap scaled to target size

getScaledDimensions(width, height, maxSize): Pair<Int, Int>

Computes resized dimensions while preserving aspect ratio.

Behavior:

  • If both dimensions ≤ maxSize: returns original size
  • Otherwise scales largest dimension down to maxSize

Output:

  • (newWidth, newHeight)

getBitmapFromUri(context, uri, maxSize): Bitmap

Loads and decodes a bitmap from a content URI with size constraints.

Behavior:

  • Uses ImageDecoder
  • Applies getScaledDimensions
  • Decodes bitmap at target resolution
  • Returns mutable ARGB_8888 copy

Output:

  • Decoded and rescaled bitmap

cropFaces(bitmap, boxes): List

Extracts face regions from bounding boxes.

Behavior:

  • Clamps box coordinates to bitmap bounds
  • Skips invalid boxes
  • Crops sub-bitmaps per bounding box

Output:

  • List of cropped face bitmaps

nms(boxes, scores, iouThreshold): List

Non-Maximum Suppression for filtering overlapping bounding boxes.

Behavior:

  • Sorts boxes by confidence score
  • Iteratively removes boxes with IoU above threshold
  • Keeps highest scoring non-overlapping boxes

Output:

  • Indices of selected boxes

drawBoxes(bitmap, boxes, color, margin, strokeWidth): Bitmap

Draws bounding boxes onto a bitmap.

Behavior:

  • Creates mutable bitmap copy
  • Draws rectangles using Canvas
  • Applies optional margin expansion
  • Uses stroke-only rendering

Output:

  • Annotated bitmap with drawn boxes

VideoUtils

Utilities for extracting frames from video files.

extractFramesFromVideo(context, videoUri, width, height, frameCount): List?

Extracts evenly spaced frames from a video.

Behavior:

  • Uses MediaMetadataRetriever
  • Computes video duration
  • Samples frames at uniform timestamps
  • Scales frames to (width, height)
  • Stops early if frame decoding fails
  • Returns null on error or empty result

Execution:

  • Runs on Dispatchers.IO

Output:

  • List of extracted video frames or null

Design Notes

  • Frame extraction is time-based sampling (not scene detection)
  • Designed for embedding pipelines requiring representative video frames
  • Face utilities assume rectangular bounding boxes in pixel coordinates
  • NMS implementation is linear after sorting (simple greedy suppression)
  • All image outputs use mutable ARGB_8888 format for downstream processing