SVG Filters Color Manipulation Filters: Monotone


Example

<svg width="800px" height="600px">
   <defs>
     <filter id="greyscale">
     <feColorMatrix type="matrix"
             values=".2  .2  .2  0 0
                     .6  .6  .6  0 0
                     .2  .2  .2  0 0
                     0 0 0 1 0"/>
     </filter> 
   </defs>
        
   <image xlink:href="https://upload.wikimedia.org/wikipedia/commons/a/af/Fruit_Stall_in_Barcelona_Market.jpg" x="20px" y="20px" width="300px" height="200px" preserveAspectRatio="xMinYMin meet" />
   <image filter="url(#greyscale)" xlink:href="https://upload.wikimedia.org/wikipedia/commons/a/af/Fruit_Stall_in_Barcelona_Market.jpg" x="340px" y="20px" width="300px" height="200px" preserveAspectRatio="xMinYMin meet"/>
</svg>

enter image description here
(Source image by Daderot at Wikimedia Commons)