[Editor] Pass a buffer instead of a blob url to the ML api

src/display/editor/stamp.js

@@ -441,15 +441,14 @@ class StampEditor extends AnnotationEditor {
         width,
         height
       );
-      offscreen.convertToBlob().then(blob => {
-        const fileReader = new FileReader();
-        fileReader.onload = () => {
-          const url = fileReader.result;
       this._uiManager
         .mlGuess({
           service: "image-to-text",
           request: {
-                imageData: url,
+            data: ctx.getImageData(0, 0, width, height).data,
+            width,
+            height,
+            channels: 4,
           },
         })
         .then(response => {
@@ -458,9 +457,6 @@ class StampEditor extends AnnotationEditor {
             this.altTextData = { altText, decorative: false };
           }
         });
-        };
-        fileReader.readAsDataURL(blob);
-      });
     }
     const ctx = canvas.getContext("2d");
     ctx.filter = this._uiManager.hcmFilter;