Using “vector-like” raster images in PDF documents

I’m in the process of producing QR-codes for use on product packaging. The codes are generated in batch and the resulting files are typically 25×25 px PNG files. Of course, such a small image would normally be way too low res to use in print, i.e. a 1×1 inch image would need to be 300×300 px in order to print in 300 DPI.

When it comes to simple images such as QR-codes (I guess this would also apply to bar codes without the digits) I realized that the actual resolution of the image is not really relevant, as I can easily resize the image to any size I prefer using nearest-neighbor resizing option in Photoshop. In a way, the resulting 250×250 px image won’t contain any more information in terms of “QR pixels” than the 25×25 px version, apart from the obvious fact that the file will be larger in size. Also, when resizing to a width not evenly divisible by 25 (e.g. 70×70) the resulting QR pixels will not all be the exact same width.

This has got me thinking I can simply place the 25×25 px PNG in my InDesign layout, which will in turn be exported to PDF and sent to print. This seems to work out fine when I print the file on my printer, but on screen the image sometimes looks blurred (as you would expect with it being magnified). I have found that the blurring effect stems from the anti-aliasing setting in my PDF viewer, so there is obviously no information about resizing/anti-aliasing embedded in the PDF file, while the printer will resize the image without anti-aliasing (i.e. using nearest neighbor).

Finally, the question: Is there any obvious downside to using this method? Is it safe to assume that the 25×25 px image in my PDF document will be upscaled without anti-aliasing when I send it to the printing office? Would I be better off just manually upscaling it or converting it to a true vector format?

Bonus question: is there a better term for what I am referring to as vector-like in the title/question, that is the concept of a bitmap/raster image being upscaled without loss of quality?

Answer

Never rely on any print provider to do anything other than spit out your file as it currently exists. I would never trust that something will be output in a specific manner to ensure it is as I expect. If you have to provide instructions or notes on how to output, then it’s a recipe for error. If you place a 25ppi image in Indesign it never gets “upsampled” when generating a PDF. It is output at 25ppi.

For codes, bar codes, QRT codes, etc their are only 2 acceptable solutions….

  1. Use a true vector code. There are dozens of barcode/QRcode
    generators which generate EPS, SVG, or EMF files. This is what you
    should use. If you’re generator can not create these formats, find
    another code generator.

  2. If you must use a raster image, then it needs to be larger than what
    will be produced. So for a 70×70 pixel code, you need a 290×290 pixel native
    image. That is to say, an original image which is 290×290, not a resized image you created. Then you could place and reduce it to 70×70 pixels in Indesign. Which will essentially increase the DPI upon output. Although, I still feel like #1 is always the better option.

Codes need to be precise. There’s no wiggle room to just get it “looking good”. A scanner may not read it properly if it’s even the slightest bit incorrect.

As for the better term…. vector-like is really non-sensical. Something is either vector or it’s not. I’d refer to it as simply non-anti-aliased raster art.

Attribution
Source : Link , Question Author : Simon , Answer Author : Scott

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