PNG QR code to 100k Black

[Mateomono]

Hi everyone,

I am working on a print project that includes QR codes. The printer informed me that all QR codes need to be 100% K black. How can I set this up in Photoshop? I know how to do this with an SVG file, but I only have PNGs for the QR codes. I just want to make sure it's done correctly and that the QR codes remain scannable once printed. 

Thank you very much for your help!

[D Fosse]

100K applies to CMYK, so PNGs can't be used. PNG doesn't support CMYK. Once you have a CMYK document it's simple. Just make sure it's 100% in the K channel, and zero in the other three.

That said, a QR code should normally be made as a vector object. Anything involving vector elements and text shouldn't be made in Photoshop in the first place. Then you make it in InDesign, placing elements created in Photoshop or Illustrator as needed.

[Mateomono]

@D FosseSo, I would need to convert it to CMYK in Photoshop?

Since a vector would be better, is there a way to convert it in InDesign? Maybe something like Image Trace? Unfortunately, I can't get new QR codes and am stuck with the provided PNG versions. Also, the QR codes don’t have text.

[Stephen Marsh]

@D FosseSo, I would need to convert it to CMYK in Photoshop?

By @Mateomono

Yes, but more work than that would be required. There are many valid variations on the following steps to get to a 0cmy100k QR code:

1. Select any of the R, G or B channels and copy it to the clipboard.
2. Convert to CMYK mode.
3. Fill the image with white, deleting everything.
4. Select the K channel.
5. Paste in the clipboard content.

You will then get something like this:

You can record these steps into an action and use it on multiple images from the action or running the action via the Batch command or Image Processor script etc.

[Mateomono]

@Stephen MarshThank you for the explanation! Great, then I will do that, and it should fix my issue. One question I still have—would it be wise to consider image tracing the PNG in Illustrator so that it becomes a vector and can easily be changed to 100K black?

[D Fosse]

It depends on whether it would ever need to be scaled in any way. QR codes, barcodes etc need to be perfectly crisp and sharp, and if it's a pixel image any scaling will blur it. Vector data, OTOH, are always sharp at any reproduction size.

[Mateomono]

@D FosseBut could that cause any issues for my QR code if I do that? The last thing I want is for it to become unscannable.

[Stephen Marsh]

@Stephen MarshThank you for the explanation! Great, then I will do that, and it should fix my issue. One question I still have—would it be wise to consider image tracing the PNG in Illustrator so that it becomes a vector and can easily be changed to 100K black?

By @Mateomono

I wouldn't do so.

What is the final reproduction size that the QR code will be printed?

For example, let's say that it's 1 inch.

In Photoshop, go to Image > Image Size and uncheck "Resample Image" and change the size to 1 inch. What is the effective resolution of the image at this size? Most lineart would be expected to have 600 ppi or higher resolution, however, this is more critical for diagonals or curves than horizontal and vertical edges.

If your QR code only contains horizontal and vertical pixels, then it should be pure solid black with no shades of gray; you don't want a fuzzy, screened edge when printed. You can always apply a 50% threshold adjustment to the image to force it to pure white/black.

For such art, the only appropriate upscaling is using Nearest Neighbour resampling/interpolation to preserve the original pixel structure, using even multiples of the original resolution or pixel count, so 200% or if the original image was 866 px wide then resample to 1732 px wide etc.

[Mateomono]

@Stephen Marsh  

This is how it looks.

Also, your explanation from before was clear, but somehow I’m struggling with the last steps. How does it turn into 100K black after pasting it? Are there any tutorials you would recommend on this?

[Mateomono]

@Stephen Marsh

Also, someone recommended that I do this for my QR codes. Is this a possible option?

I've already posted the best format, but take your image (ideally, high resolution), convert to grayscale, then convert to bitmap mode using 50% threshold, save as LZW-compressed TIFF. This will be black only and the white areas will be transparent if you desire. The TIFF can be colored in InDesign if desired (as long as you have correct contrast between code and background). If you have a number of these, you can create a batch process in Photoshop.

[Stephen Marsh]

@Stephen Marsh

Also, someone recommended that I do this for my QR codes. Is this a possible option?

I've already posted the best format, but take your image (ideally, high resolution), convert to grayscale, then convert to bitmap mode using 50% threshold, save as LZW-compressed TIFF. This will be black only and the white areas will be transparent if you desire. The TIFF can be colored in InDesign if desired (as long as you have correct contrast between code and background). If you have a number of these, you can create a batch process in Photoshop.

By @Mateomono

That is also a viable approach and will create much smaller file sizes than working with CMYK 8bpc data. Run with that!

[Stephen Marsh]

Do you know that such size codes can be successfully read? What print method is being used (offset lithography, digital toner laser printer, inkjet printer etc).

The 1400+ resolution should be fine at that size as long as the code isn't scaled larger than 36mm in layout software or resampled when making a PDF from layout or processing at the RIP/DFE.

[Stephen Marsh]

@Stephen Marsh  

Also, your explanation from before was clear, but somehow I’m struggling with the last steps. How does it turn into 100K black after pasting it? Are there any tutorials you would recommend on this?

By @Mateomono

The copied data is black, so if you paste it into the targeted/selected active black channel of a white filled CMYK mode file the same pixel dimensions as the original the data will be K only.