能否通过Google Vision API选中特定文本？相机扫描应用开发咨询

Absolutely, you can totally implement touch-based focus to target only the "Hello World" text in your camera feed! Let’s break down how to make this work step by step:

• First, when the user taps the screen, grab the exact x/y coordinates of the touch event. On Android, use an OnTouchListener to pull values from MotionEvent; on iOS, a UITapGestureRecognizer will give you the tap point relative to the camera preview view.
• Convert these screen coordinates to match the camera's actual frame (you’ll need to adjust for preview scaling, aspect ratio, and device orientation since the preview might not match the raw camera output exactly).

• Once you have the adjusted coordinates, define a small bounding box around the tap (like a 200x200 pixel square centered on the tap point). This way, you’re only sending a cropped snippet of the camera frame to the Vision API instead of the entire image—greatly reducing irrelevant text detection.
• For example, on Android, you can create a cropped Bitmap from the full camera frame before passing it to the TextRecognizer.

• Even with cropping, the API might pick up small bits of other text. Add a post-processing step to filter results:
  • Iterate through the TextBlock objects returned by the Vision API.
  • Check if any block contains the exact string "Hello World" (or use a case-insensitive match if needed).
  • If found, extract your desired details; if not, you can either ignore the result or prompt the user to tap closer to the target text.

• To make the experience intuitive, draw a rectangle on the preview screen at the tap location. This lets the user see exactly which area is being scanned, helping them align their tap perfectly with "Hello World".

Here’s a quick code example to illustrate the touch capture and cropping flow:

cameraPreview.setOnTouchListener { _, event ->
    if (event.action == MotionEvent.ACTION_UP) {
        val tapX = event.x
        val tapY = event.y
        
        // Convert screen tap coordinates to match camera preview dimensions
        val scaledX = tapX * cameraPreview.width / cameraPreview.measuredWidth
        val scaledY = tapY * cameraPreview.height / cameraPreview.measuredHeight
        
        // Define a 200x200 crop box centered on the tap
        val cropSize = 100
        val cropLeft = max(0, scaledX - cropSize).toInt()
        val cropTop = max(0, scaledY - cropSize).toInt()
        val cropRight = min(cameraPreview.width, scaledX + cropSize).toInt()
        val cropBottom = min(cameraPreview.height, scaledY + cropSize).toInt()
        
        // Crop the original camera frame bitmap
        val croppedBitmap = Bitmap.createBitmap(originalCameraFrame, cropLeft, cropTop, cropRight - cropLeft, cropBottom - cropTop)
        
        // Send cropped bitmap to Vision API for processing
        scanTargetText(croppedBitmap)
    }
    true
}

private fun scanTargetText(bitmap: Bitmap) {
    val textRecognizer = TextRecognizer.Builder(context).build()
    val imageFrame = Frame.Builder().setBitmap(bitmap).build()
    val recognitionResult = textRecognizer.detect(imageFrame)
    
    for (textBlock in recognitionResult.textBlocks) {
        if (textBlock.text.trim().equals("Hello World", ignoreCase = true)) {
            // Target text found! Handle your detail extraction here
            Log.d("TextScanner", "Found Hello World! Full block text: ${textBlock.text}")
            break
        }
    }
}

内容的提问来源于stack exchange，提问作者Syed Ammar