These examples show how changing the threshold values affect the rendering of the same image:

Red, Green & Blue with Black outline on a White background

<FILE FILENAME="COMPASS.PNG" FILETYPE="PNG" />

Red, Green & Blue shown as White

<FILE FILENAME="COMPASS.PNG" FILETYPE="PNG" MONOCHROME="25" />

Red shown as Black; Green & Blue shown as White

<FILE FILENAME="COMPASS.PNG" FILETYPE="PNG" MONOCHROME="50" />

Red & Green shown as Black; Blue shown as White

<FILE FILENAME="COMPASS.PNG" FILETYPE="PNG" MONOCHROME="100" />

Red, Green & Blue shown as Black

<FILE FILENAME="COMPASS.PNG" FILETYPE="PNG" MONOCHROME="200" />

 

Links:

MONOCHROME