mention that screenshots file must be noraw

diff --git a/pctb/structure.c b/pctb/structure.c
index 8887c8ad624dde26d7704cca2384b0167933acc3..94c6b42aa6e84f2c9b5b69d41f26444aaecfcb94 100644 (file)
--- a/pctb/structure.c
+++ b/pctb/structure.c
@@ -387,7 +387,7 @@ static void file_read_image_ppm(FILE *f) {
   if (!(inpam.maxval == 255 &&
        inpam.bytes_per_sample == 1 &&
        inpam.format == RPPM_FORMAT))
-    fatal("PNM screenshot(s) file must be 8bpp 1 byte per sample RGB");
+    fatal("PNM screenshot(s) file must be 8bpp 1 byte-per-sample RGB raw");
 
   CANONICALISE_IMAGE(im, inpam.width, inpam.height, {
     int r= fread(&rgb_buf,1,3,f);