Generating PDF shows border around background transitions

[JohnnyClutch]

I have many pngs that I'm combining into a business logic driven diagram using an html canvas (via Konva.js). I get the canvas the way I need it then call:

const pdfDoc = await PDFDocument.create();
pdfDoc.addPage(page);
const pdfBytes = await pdfDoc.save();
const file: Blob = new Blob([ pdfBytes ], { type: 'application/pdf' });
const fileURL = URL.createObjectURL(file);
window.open(fileURL);

As stated above, the images I use are "blocks" that I combine to create a single diagram, so I lay them over each other.

I tried removing the entire background color (white) of each image to transparent , but the process of doing so rendered the text in the images less than optimally readable, so I went through each image and removed the background only from areas where there wasn't any text. It looks really good in the web page.

As shown in the attachment, when I create the pdf, pdf-lib creates lines / border where the backgrounds still exists (the fainter inner border -- the darker one is intentional).