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ipa: rpi: Fix gamma lookup table generation for PiSP platform

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generateLut was failing to fill in the final slope value, meaning that
fully saturated pixels would full slightly short (the slope of the
final piecewise linear segment would default to zero).

The loop is slightly reorganised to fix the problem.

Signed-off-by: David Plowman <david.plowman@raspberrypi.com>
Reviewed-by: Nick Hollinghurst <nick.hollinghurst@raspberrypi.com>
Reviewed-by: Naushir Patuck <naush@rasbperrypi.com>
Signed-off-by: Kieran Bingham <kieran.bingham@ideasonboard.com>
This commit is contained in:
David Plowman
2026-03-27 09:02:43 +00:00
committed by Kieran Bingham
parent 3c08aaef14
commit 033bb2cce3
1 changed files with 19 additions and 25 deletions
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44
src/ipa/rpi/pisp/pisp.cpp
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@@ -80,36 +80,30 @@ int generateLut(const ipa::Pwl &pwl, uint32_t *lut, std::size_t lutSize,
if (pwl.empty())
return -EINVAL;
int lastY = 0;
int nextY = pwl.eval(0);
for (unsigned int i = 0; i < lutSize; i++) {
int x, y;
if (i < 32)
x = i * 512;
else if (i < 48)
x = (i - 32) * 1024 + 16384;
unsigned int nextI = i + 1;
int nextX;
if (nextI < 32)
nextX = nextI * 512;
else if (nextI < 48)
nextX = (nextI - 32) * 1024 + 16384;
else
x = std::min(65535u, (i - 48) * 2048 + 32768);
nextX = (nextI - 48) * 2048 + 32768;
y = pwl.eval(x);
if (y < 0 || (i && y < lastY)) {
LOG(IPARPI, Error)
<< "Malformed PWL for Gamma, disabling!";
return -1;
int y = nextY;
nextY = pwl.eval(nextX);
unsigned int slope = nextY - y;
if (slope >= (1u << SlopeBits)) {
slope = (1u << SlopeBits) - 1;
LOG(IPARPI, Info)
<< "Maximum Gamma slope exceeded, adjusting!";
nextY = y + slope;
}
if (i) {
unsigned int slope = y - lastY;
if (slope >= (1u << SlopeBits)) {
slope = (1u << SlopeBits) - 1;
LOG(IPARPI, Info)
<< ("Maximum Gamma slope exceeded, adjusting!");
y = lastY + slope;
}
lut[i - 1] |= slope << PosBits;
}
lut[i] = y;
lastY = y;
lut[i] = y | (slope << PosBits);
}
return 0;