From d7bab9ba9f7981b3e1710f88ec25df9200c5e11d Mon Sep 17 00:00:00 2001
From: rom9 <4711834+rom9@users.noreply.github.com>
Date: Fri, 28 Jun 2019 20:44:40 +0200
Subject: [PATCH] Changed `channelsAverage()` to sample values from the
 original data in the RawImage instance, taking into account black levels.
 This lets me completely revert my awful commit 22f6297a5 and clip values to
 65535, as it should be to avoid trouble downstream.

---
 rtengine/filmnegativeproc.cc | 17 +++++++----------
 1 file changed, 7 insertions(+), 10 deletions(-)

diff --git a/rtengine/filmnegativeproc.cc b/rtengine/filmnegativeproc.cc
index 555a47506..4abe32b86 100644
--- a/rtengine/filmnegativeproc.cc
+++ b/rtengine/filmnegativeproc.cc
@@ -49,6 +49,7 @@ bool channelsAvg(
     int width,
     int height,
     array2D<float>& rawData,
+    const float* cblacksom,
     rtengine::Coord spotPos,
     int spotSize,
     const rtengine::procparams::FilmNegativeParams& params,
@@ -83,13 +84,9 @@ bool channelsAvg(
 
             ++pxCount[ch];
 
-            // If film negative is currently enabled, undo the effect by elevating to 1/exp,
-            // in order to sample the original, linear value
-            if (params.enabled) {
-                avgs[ch] += powf(rawData[r][c], -1.f / (ch == 0 ? params.redExp : ch == 1 ? params.greenExp : params.blueExp));
-            } else {
-                avgs[ch] += rawData[r][c];
-            }
+            // Sample the original unprocessed values from RawImage, subtracting black levels.
+            // Scaling is irrelevant, as we are only interested in the ratio between two spots.
+            avgs[ch] += ri->data[r][c] - cblacksom[ch];
         }
     }
 
@@ -118,13 +115,13 @@ bool rtengine::RawImageSource::getFilmNegativeExponents(Coord2D spotA, Coord2D s
 
     // Sample first spot
     transformPosition(spotA.x, spotA.y, tran, spot.x, spot.y);
-    if (!channelsAvg(ri, W, H, rawData, spot, spotSize, currentParams, clearVals)) {
+    if (!channelsAvg(ri, W, H, rawData, cblacksom, spot, spotSize, currentParams, clearVals)) {
         return false;
     }
 
     // Sample second spot
     transformPosition(spotB.x, spotB.y, tran, spot.x, spot.y);
-    if (!channelsAvg(ri, W, H, rawData, spot, spotSize, currentParams, denseVals)) {
+    if (!channelsAvg(ri, W, H, rawData, cblacksom, spot, spotSize, currentParams, denseVals)) {
         return false;
     }
 
@@ -263,7 +260,7 @@ void rtengine::RawImageSource::filmNegativeProcess(const procparams::FilmNegativ
         printf("Median calc time us: %d\n", t3.etime(t2));
     }
 
-    constexpr float CLIP_VAL = 20 * MAX_OUT_VALUE;
+    constexpr float CLIP_VAL = 65535.f;
 
     t3.set();