How can I improve ReportLab image quality?

Question

I'm building a label printer. It consists of a logo and some text, not tough. I have already spent 3 days trying to get the original SVG logo to draw to screen but the SVG is too complex, using too many gradients, etc.

So I have a high quality bitmapped logo (as a JPG or PNG) and I'm drawing that on a ReportLab canvas. The image in question is much larger than 85*123px. I did this hoping ReportLab would embed the whole thing and scale it accordingly. Here's how I'm doing it:

canvas.drawImage('logo.jpg', 22+xoffset, 460, 85, 123)

The problem is, my assumption was incorrect. It seems to scale it down to 85*123px at screen resolution and that means when it's printed, it doesn't look great.

Does ReportLab have any DPI commands for canvases or documents so I can keep the quality sane?

Answer 1

Having previously worked at the ReportLab company, I can tell you that raster images do not go through any automatic resampling/downscaling while being included in the PDF. The 85*123 dimensions you are using are not pixels, but points (pt) which are a physical unit like millimetres or inches.

I would suggest printing the PDF with different quality images to confirm this or otherwise zooming in very, very far using your PDF viewer. It will always look a bit fuzzy in a PDF viewer as the image is resampled twice (once in the imaging software and then again to the pixels available to the PDF viewer).

This is how I would calculate what size in pixels to make a raster image for it to print well at a given physical size:

Assume I want the picture to be 2 inches wide, there are 72 points in a inch so the width in my code would be 144. I know that a good crisp resolution to print at is 300dpi (dots per inch) so the raster image is saved at 600px wide.

Answer 2

One option that I thought of while writing the question is: increase the size of the PDF and let the printer sort things out.

If I just multiplied all my numbers by 5 and the printer did manage to figure things out, I'd have close to 350DPI... But I'm making quite an assumption.