public int FastMbAnalyze(int quality)
{
// Empirical cut-off value, should be around 16 (~=block size). We use the
// [8-17] range and favor intra4 at high quality, intra16 for low quality.
int q = quality;
int kThreshold = 8 + ((17 - 8) * q / 100);
int k;
Span <uint> dc = stackalloc uint[16];
uint m;
uint m2;
for (k = 0; k < 16; k += 4)
{
LossyUtils.Mean16x4(this.YuvIn.AsSpan(YOffEnc + (k * WebpConstants.Bps)), dc.Slice(k, 4));
}
for (m = 0, m2 = 0, k = 0; k < 16; k++)
{
m += dc[k];
m2 += dc[k] * dc[k];
}
if (kThreshold * m2 < m * m)
{
this.SetIntra16Mode(0); // DC16
}
else
{
byte[] modes = new byte[16]; // DC4
this.SetIntra4Mode(modes);
}
return(0);
}
private static void RunMean16x4Test()
{
// arrange
byte[] input =
{
154, 145, 102, 115, 127, 129, 126, 125, 126, 120, 133, 152, 157, 153, 119, 94, 104, 116, 111, 113,
113, 109, 105, 124, 173, 175, 177, 170, 175, 172, 166, 164, 151, 141, 99, 114, 125, 126, 135, 150,
133, 115, 127, 149, 141, 168, 100, 54, 110, 117, 115, 116, 119, 115, 117, 130, 174, 174, 174, 157,
146, 171, 166, 158, 117, 140, 96, 111, 119, 119, 136, 171, 188, 134, 121, 126, 136, 119, 59, 77,
109, 115, 113, 120, 120, 117, 128, 115, 174, 173, 173, 161, 152, 148, 153, 162, 105, 140, 96, 114,
115, 122, 141, 173, 190, 190, 142, 106, 151, 78, 66, 141, 110, 117, 123, 136, 118, 124, 127, 114,
173, 175, 166, 155, 155, 159, 159, 158
};
uint[] dc = new uint[4];
uint[] expectedDc = { 1940, 2139, 2252, 1813 };
// act
LossyUtils.Mean16x4(input, dc);
// assert
Assert.True(dc.SequenceEqual(expectedDc));
}
