libtiff: tiffcp: preserve TIFFTAG_REFERENCEBLACKWHITE when doing YCbCr JPEG -> YCbCr JPEG

SDL Commits
1 
From 86d31b233b78be10929ce29d9f286009eb99e728 Mon Sep 17 00:00:00 2001
From: Even Rouault <[EMAIL REDACTED]>
Date: Sun, 8 Oct 2023 20:20:04 +0200
Subject: [PATCH] tiffcp: preserve TIFFTAG_REFERENCEBLACKWHITE when doing YCbCr
 JPEG -> YCbCr JPEG

---
 tools/tiffcp.c | 6 ++++++
 1 file changed, 6 insertions(+)

diff --git a/tools/tiffcp.c b/tools/tiffcp.c
index d2dd6b17..3f761feb 100644
--- a/tools/tiffcp.c
+++ b/tools/tiffcp.c
@@ -879,6 +879,12 @@ static int tiffcp(TIFF *in, TIFF *out)
                 {
                     TIFFGetFieldDefaulted(in, TIFFTAG_YCBCRSUBSAMPLING,
                                           &subsamplinghor, &subsamplingver);
+
+                    float *refBW = NULL;
+                    if (TIFFGetField(in, TIFFTAG_REFERENCEBLACKWHITE, &refBW))
+                    {
+                        TIFFSetField(out, TIFFTAG_REFERENCEBLACKWHITE, refBW);
+                    }
                 }
                 TIFFSetField(out, TIFFTAG_YCBCRSUBSAMPLING, subsamplinghor,
                              subsamplingver);