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Merge pull request #1071 from TomHarte/EverSharper

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macOS: Accept and embrace limits of composite sharpening.
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Thomas Harte 2022-07-18 09:25:30 -04:00 committed by GitHub
commit 6579c12053
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1 changed files with 15 additions and 6 deletions
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21
OSBindings/Mac/Clock Signal/ScanTarget/CSScanTarget.mm
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@ -747,7 +747,9 @@ using BufferingScanTarget = Outputs::Display::BufferingScanTarget;
const auto chromaCoefficients = boxCoefficients(radiansPerPixel, 3.141592654f);
_chromaKernelSize = 15;
for(size_t c = 0; c < 8; ++c) {
firCoefficients[c].y = firCoefficients[c].z = (isSVideoOutput ? 2.0f : 1.0f) * chromaCoefficients[c];
// Bit of a fix here: if the pipeline is for composite then assume that chroma separation wasn't
// perfect and deemphasise the colour.
firCoefficients[c].y = firCoefficients[c].z = (isSVideoOutput ? 2.0f : 1.25f) * chromaCoefficients[c];
firCoefficients[c].x = 0.0f;
if(fabsf(chromaCoefficients[c]) < 0.01f) {
_chromaKernelSize -= 2;
@ -756,13 +758,20 @@ using BufferingScanTarget = Outputs::Display::BufferingScanTarget;
firCoefficients[7].x = 1.0f;
// Luminance will be very soft as a result of the separation phase; apply a sharpen filter to try to undo that.
// This is applied separately because the first composite processing step is going to select between the nominal
// chroma and luma parts to take the place of luminance depending on whether a colour burst was found, and high-pass
// filtering the chrominance channel would be visually detrimental.
//
// The low cut off ['Hz' but per line, not per second] is somewhat arbitrary.
// This is applied separately in order to partition three parts of the signal rather than two:
//
// 1) the luminance;
// 2) not the luminance:
// 2a) the chrominance; and
// 2b) some noise.
//
// There are real numerical hazards here given the low number of taps I am permitting to be used, so the sharpen
// filter below is just one that I found worked well. Since all numbers are fixed, the actual cutoff frequency is
// going to be a function of the input clock, which is a bit phoney but the best way to stay safe within the
// PCM sampling limits.
if(!isSVideoOutput) {
SignalProcessing::FIRFilter sharpenFilter(15, float(_lineBufferPixelsPerLine), 40.0f, colourCyclesPerLine);
SignalProcessing::FIRFilter sharpenFilter(15, 1368, 60.0f, 227.5f);
const auto sharpen = sharpenFilter.get_coefficients();
size_t sharpenFilterSize = 15;
bool isStart = true;