# CVS/Kodak Picture Kiosk Moiré



## soldrinero (May 21, 2017)

I recently needed to print a picture of myself quickly (for a Mother's Day card to my grandmother), and didn't have time to use my usual, color-managed online printing service. I decided that, since nobody around me ever sees the photographic flaws that bother me, CVS would do just fine for a 4x6 inch print.

I took the full-resolution photo that a friend gave me (from a D800) and printed it out. As expected, the skin tone was bordering on Oompa-Loompa, but what shocked me was the moiré. I was wearing a sport coat in the photo, and it was so bad it look like I had been changing oil on my car! And there was no moiré in the original - apparently the Kodak Picture Kiosk has a very poor (or simple) downsampling algorithm.

I asked at the store, and naturally no one there knew what the native PPI is for the kiosk, so I went back home into Lightroom and output five images, at 300, 250, 200, 150, and 100 ppi for a 4x6 inch image. The 150 and 100 ppi images were clearly low-resolution, as expected, but free of moiré. The 200 and 250 ppi images had acceptable resolution and no moiré (they also had better color, as apparently the two printers the kiosk prints from had very different calibrations). The 300 ppi image once again introduced moiré.

The bottom line is, Kodak Picture Kiosks appear to use a native resolution between 250 - 300 ppi, and 250 ppi appears to not risk introducing moiré. Has anyone else encountered this, or had a different experience with print kiosks?


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## privatebydesign (May 21, 2017)

Moire is frequency specific, it isn't the 300ppi resampled that is the issue, it is the specific interaction of the resampled frequency combined with the frequency of your sports coat. You could just as easily have the same problem with the same jacket at any other resampled rate if the jacket was a different size in the frame.


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## soldrinero (May 21, 2017)

privatebydesign said:


> Moire is frequency specific, it isn't the 300ppi resampled that is the issue, it is the specific interaction of the resampled frequency combined with the frequency of your sports coat. You could just as easily have the same problem with the same jacket at any other resampled rate if the jacket was a different size in the frame.



Yes, I agree that it's a frequency-specific effect and may not happen for certain resampling frequencies (or different image frequencies). But if the kiosk has a fixed printer DPI and always resamples the image to match before printing, lower PPIs will result in upsampling, while higher PPIs will require downsampling. Since only downsampling can cause moiré, there is definitely downsampling at 300 ppi.

You're right that there could be downsampling going on at one of the lower resolutions I tested and it just didn't introduce moiré. But it would have to be an even worse algorithm than I think it is to lower the resolution below 250 ppi before printing.


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