YUV to JPG Conversion

Information
Description	Code snippet for converting an Android ImageReader YUV frame to a JPG image.
Purpose	The function: Converts raw YUV image data to an RGB Bitmap Scales it down to a predefined width (220 px) while maintaining aspect ratio Compresses the bitmap to JPEG (50% quality) Returns the result as a ByteArray
Language	Kotlin

Input Parameters

yuvBytes: ByteArray The raw YUV NV21 frame data (e.g., from a camera preview).

width: Int Width of the image in pixels.

height: Int Height of the image in pixels.

Output

A ByteArray containing the compressed JPG image.

Snippet

import com.google.android.renderscript.Toolkit
// ...

fun convertYuvToJpeg(
    yuvBytes: ByteArray,
    width: Int,
    height: Int,
    quality: Int = 50,
    desiredWidth: Int = 220
): ByteArray {
    val rgbBitmap = Toolkit.yuvToRgbBitmap(yuvBytes, width, height, YuvFormat.NV21).let {
        val bitmap = if (it.width > it.height) {
            val matrix = Matrix().apply { postRotate(-90f) }
            Bitmap.createBitmap(it, 0, 0, it.width, it.height, matrix, true)
        } else it

        val desiredHeight = desiredWidth * bitmap.height / bitmap.width
        Bitmap.createScaledBitmap(bitmap, desiredWidth, desiredHeight, false)
    }

    val outputStream = ByteArrayOutputStream()
    rgbBitmap.compress(Bitmap.CompressFormat.JPEG, quality, outputStream)
    return outputStream.toByteArray()
}

Notes

The JPG compression level (i.e. quality) is adjustable. A lower value reduces the file size at the cost of image quality. Use 50% as an initial value.

The desiredWidth allows to configure the size of the JPG image. We have set this to 220px as a good compromise between file size and image resolution.

The image transformation introduces a load on the system. It's recommended to run this in a separate thread to avoid blocking the main thread and causing frame-drop while recording.

This snippet uses the com.google.android.renderscript.Toolkit dependency for the image conversion algorithm.