目标检测：解决实时预览中Bounding Box偏移问题

需求说明 #

• 实现实时预览中为多个检测目标绘制Bounding Box
• 代码简洁优雅、易于理解
• 明确背后的实现逻辑

当前问题 #

预览图与输入图尺寸不同，坐标转换后绘制的Bounding Box严重偏移，与实际目标位置不符。

现有代码 #

override fun draw(canvas: Canvas) {
    super.draw(canvas)

    // Get the dimensions of the preview image
    val previewWidth = previewImageSize.width
    val previewHeight = previewImageSize.height

    // Get the dimensions of the input image
    val inputWidth = inputImageSize.width
    val inputHeight = inputImageSize.height

    // Calculate the scaling factor for each dimension
    val scaleX: Float = previewWidth.toFloat() / inputWidth.toFloat()
    val scaleY: Float = previewHeight.toFloat() / inputHeight.toFloat()

    for (result in results) {
        val boundingBox = result.boundingBox

        val left = boundingBox.left * scaleX
        val top = boundingBox.top * scaleY
        val right = boundingBox.right * scaleX
        val bottom = boundingBox.bottom * scaleY

        // Draw bounding box around detected objects
        val drawableRect = RectF(left, top, right, bottom)
        canvas.drawRect(drawableRect, boxPaint)

        // Create text to display alongside detected objects
        val drawableText =
            result.categories[0].label + " " +
                    String.format("%.2f", result.categories[0].score)

        // Draw rect behind display text
        textBackgroundPaint.getTextBounds(drawableText, 0, drawableText.length, bounds)
        val textWidth = bounds.width()
        val textHeight = bounds.height()
        canvas.drawRect(
            left,
            top,
            left + textWidth + BOUNDING_RECT_TEXT_PADDING,
            top + textHeight + BOUNDING_RECT_TEXT_PADDING,
            textBackgroundPaint
        )

        // Draw text for detected object
        canvas.drawText(drawableText, left, top + bounds.height(), textPaint)
    }
}

补充信息 #

• 输入图像尺寸：320x320（由预览图缩放后传入模型）
• 预览尺寸：1857x1080（1857为高度）
• CameraX获取的ImageAnalysis图像尺寸：640x480
• 计算得到的缩放因子：scaleX=3.375，scaleY=5.803125

内容的提问来源于stack exchange，提问作者MaaAn13