From 54bfa23025397b10e7fede996518e9268521c41e Mon Sep 17 00:00:00 2001
From: John Cupitt <jcupitt@gmail.com>
Date: Sun, 3 May 2020 12:31:17 +0100
Subject: [PATCH] warn against thumbnail_image

see https://github.com/libvips/libvips/issues/1637#issuecomment-623094732
---
 libvips/resample/thumbnail.c | 7 ++++++-
 1 file changed, 6 insertions(+), 1 deletion(-)

diff --git a/libvips/resample/thumbnail.c b/libvips/resample/thumbnail.c
index b4711da46c..cfa4da975f 100644
--- a/libvips/resample/thumbnail.c
+++ b/libvips/resample/thumbnail.c
@@ -1520,7 +1520,12 @@ vips_thumbnail_image_init( VipsThumbnailImage *image )
  * * @export_profile: %gchararray, export ICC profile
  * * @intent: #VipsIntent, rendering intent
  *
- * Exacty as vips_thumbnail(), but read from an existing image.
+ * Exacty as vips_thumbnail(), but read from an existing image. 
+ *
+ * This operation
+ * is not able to exploit shrink-on-load features of image load libraries, so
+ * it can be much slower than `vips_thumbnail()` and produce poorer quality
+ * output. Only use it if you really have to.
  *
  * See also: vips_thumbnail().
  *