Steps to reproduce the problem:
1. When using the demo application - https://mozilla.github.io/pdf.js/web/viewer.html, load  the document 5311693-1.pdf

[5311693-1.pdf](https://github.com/mozilla/pdf.js/files/5137225/5311693-1.pdf)

2. go to Page 16 of the document.

3.  The strip of  EKG data  appears to have an incorrect line width   under the  Multi-color heat rate chart.

4.  When the same document is generated by pdffactory ,  the artifact are not visible.

What is the expected behavior? (add screenshot)
![expected](https://user-images.githubusercontent.com/3577617/91461157-4622cb80-e84e-11ea-8e5d-750c7b4e64ae.PNG)

What went wrong? (add screenshot)
The EKG line strip  has an incorrect thickness.  the x-transform seems to stretch the line thickness.  See the  stri in the RED rectagngle of the attached behavior versus the GREEN rectangle

Link to a viewer (if hosted on a site other than mozilla.github.io/pdf.js or as Firefox/Chrome extension):
 https://mozilla.github.io/pdf.js/web/viewer.html
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      ) {
        imgToPaint = imgData;
      } else {
        tmpCanvas = this.cachedCanvases.getCanvas("inlineImage", width, height);
        tmpCtx = tmpCanvas.context;
        putBinaryImageData(tmpCtx, imgData, this.current.transferMaps);
        imgToPaint = tmpCanvas.canvas;
      }
      let paintWidth = width,
        paintHeight = height;
      let tmpCanvasId = "prescale1";
      
      
      
      while (
        (widthScale > 2 && paintWidth > 1) ||
        (heightScale > 2 && paintHeight > 1)
      ) {
        let newWidth = paintWidth,
          newHeight = paintHeight;
        if (widthScale > 2 && paintWidth > 1) {
          newWidth = Math.ceil(paintWidth / 2);
          widthScale /= paintWidth / newWidth;
        }
        if (heightScale > 2 && paintHeight > 1) {
          newHeight = Math.ceil(paintHeight / 2);
          heightScale /= paintHeight / newHeight;
        }
        tmpCanvas = this.cachedCanvases.getCanvas(