From b2feb4805fa6ca46978b81176b7b96ecbace76b6 Mon Sep 17 00:00:00 2001
From: John Cupitt <jcupitt@gmail.com>
Date: Thu, 18 Jun 2020 14:54:09 +0100
Subject: [PATCH] fix flush of left-over bits

we were not adjusting for pixel size, thanks MathemanFlo

see https://github.com/libvips/libvips/pull/1672#issuecomment-644807739
---
 libvips/foreign/vips2tiff.c | 10 ++++++++--
 1 file changed, 8 insertions(+), 2 deletions(-)

diff --git a/libvips/foreign/vips2tiff.c b/libvips/foreign/vips2tiff.c
index ea939e6d..5ff5834d 100644
--- a/libvips/foreign/vips2tiff.c
+++ b/libvips/foreign/vips2tiff.c
@@ -1310,8 +1310,14 @@ eightbit2nbit( Wtiff *wtiff, VipsPel *q, VipsPel *p, int n )
 
 	/* Any left-over bits? Need to be left-aligned.
 	 */
-	if( (x & pixel_mask) != 0 ) 
-		*q++ = (bits ^ mask) << (8 - (x & pixel_mask));
+	if( (x & pixel_mask) != 0 ) {
+		/* The number of bits we've collected in bits and must
+		 * left-align and flush.
+		 */
+		int collected_bits = (x & pixel_mask) << (wtiff->bitdepth - 1);
+
+		*q++ = (bits ^ mask) << (8 - collected_bits);
+	}
 }
 
 /* Swap the sense of the first channel, if necessary.