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
}
        }
        ctx.putImageData(chunkImgData, 0, j);
        j += FULL_CHUNK_HEIGHT;
      }
      if (i < totalChunks) {
        elemsInThisChunk = width * partialChunkHeight * 4;
        dest.set(src.subarray(srcPos, srcPos + elemsInThisChunk));
        if (hasTransferMaps) {
          for (let k = 0; k < elemsInThisChunk; k += 4) {
            if (transferMapRed) {
              dest[k + 0] = transferMapRed[dest[k + 0]];
            }
            if (transferMapGreen) {
              dest[k + 1] = transferMapGreen[dest[k + 1]];
            }
            if (transferMapBlue) {
              dest[k + 2] = transferMapBlue[dest[k + 2]];
            }
          }
        }
        ctx.putImageData(chunkImgData, 0, j);
      }
    } else if (imgData.kind === ImageKind.RGB_24BPP) {
      
      const hasTransferMaps = !!(
        transferMapRed ||
        transferMapGreen ||
        transferMapBlue
      );