Packing to and from 8bit array

packing.cs

void Main()
{
	const int bytesPer8bitScanline = 300;
	const int bytesPerScanline = 38;
	const int bits = 1;
	Random r = new Random();

	byte[] source = new byte[bytesPer8bitScanline];
	for (int i = 0; i < source.Length; i++)
	{
		source[i] = (byte)r.Next(0, 2);
	}

	TryScaleDownFrom8BitArray(source, bytesPerScanline, bits, out byte[] temp);

	TryScaleUpTo8BitArray(temp, bytesPerScanline, bits, out byte[] destination);

	// We're getting difference here. What is wrong?
	for (int i = 0; i < source.Length; i++)
	{
		if (source[i] != destination[i])
		{
			$"{source[i]} != {destination[i]} at {i}".Dump();
		}
	}

	source.Dump();
	destination.Dump();
}

// This should be correct. We're using it to correctly decode pngs
private bool TryScaleUpTo8BitArray(byte[] source, int bytesPerScanline, int bits, out byte[] buffer)
{
	if (bits >= 8)
	{
		buffer = null;
		return false;
	}

	buffer = new byte[bytesPerScanline * 8 / bits];
	byte[] result = buffer;
	int mask = 0xFF >> (8 - bits);
	int resultOffset = 0;

	for (int i = 0; i < bytesPerScanline; i++)
	{
		byte b = source[i];
		for (int shift = 0; shift < 8; shift += bits)
		{
			int index = (b >> (8 - bits - shift)) & mask;
			result[resultOffset] = (byte)index;

			resultOffset++;
		}
	}

	return true;
}

// This appears to be incorrect.
private bool TryScaleDownFrom8BitArray(byte[] source, int bytesPerScanline, int bits, out byte[] result)
{
	if (bits >= 8)
	{
		result = null;
		return false;
	}

	result = new byte[bytesPerScanline];

	byte mask = (byte)(0xFF >> (8 - bits));
	byte shift0 = (byte)(8 - bits);
	int shift = 8 - bits;
	int v = 0;
	int resultOffset = 0;

	for (int i = 0; i < source.Length; i++)
	{
		int value = source[i] & mask;
		v |= (value << shift);

		if (shift == 0)
		{
			shift = shift0;
			result[resultOffset] = (byte)v;
			resultOffset++;
			v = 0;
		}
		else
		{
			shift -= bits;
		}
	}

	if (shift != shift0)
	{
		result[0] = (byte)v;
	}

	return true;
}

When I run the above sample in LinqPad i'm getting differences in the source and destination arrays. They should match. I've no idea why.

Should result[0] = (byte)v; not be result[resultOffset] = (byte)v?

Relevant ImageSharp PR https://github.com/SixLabors/ImageSharp/pull/712/files#r220508943

Ah @dlemstra You're the man!! Can't believe I missed this.