added link to grayscale image conversion tool

README.md

@@ -42,6 +42,7 @@ video of a an [animation using the tek4010](https://youtu.be/7FMewaoEOmk), a vid
         - Full screen resolution in -full mode
         - Coordinate system: 1024 x 780 and 4096 x 3072 tek points
         - All Tektronix 4014 modes, including graphical input mode (GIN) and write-through mode
+	- Supports grayscale images (Tektronix 4014 intensity chart)
         - APL character set and keyboard for Tektronix 4013 and Tektronix 4015
         - telnet and rsh connection to host and direct display of plot files
         - baud rates: 300 to 19200
@@ -463,6 +464,15 @@ ARDS manual (see manuals folder)
 The font used by tek4010 is defined in tube.h. If you prefer to use a different font (for example a
 dotted font), define STANDARD_FONT and STANDARD_FONT_SIZE in tube.h and recompile the program.
 
+**Making grayscale images for tek4010**
+
+The Tektronix 4014 was able to display grayscale images using the "special point plot mode", which was
+state of the art for the 1970s. The grayscale had only 64 values and was very nonlinear. There are
+very few such grayscale images still available, but you can make your own images using my tool
+[make-tek-image](https://github.com/rricharz/make-tek-image).
+
+![screen_shot](spock.png?raw=true "tek4010 screendump")
+
 **Help wanted**
 
 I am interested to find any recoverable original software using the graphical input modes of the