Moire effect when viewing PDF via web browser
April 25, 2020 9:31 PM Subscribe
Why does a moire effect appear on a PDF only when viewing in a web browser? The PDF needs to be viewed by a client online, but eventually will be printed in a book. Google-fu has failed me!
Consider that an image is a rectangular grid of dots, and the viewing apparatus (laptop screen, printout) is another grid.
A moire effect is the result of two overlapping grids, say the gridlike features in your image and then the gridlike display of your viewing apparatus. Where the spacing of grids is intrinsically important. For two different viewing apparatuses, two different effects. The web browser representation (and laptop screen) has one spacing, the final printed book will have another, some image viewing application has another. If you think of your pdf viewer and printer as a traditional moire effect with grids printed on plastic sheets, you're essentially swapping in a different plastic sheet with hugely grid spacing and noticing the effect goes away. Or maybe swapping both sheets at once.
> The PDF needs to be viewed by a client online, but eventually will be printed in a book. Google-fu has failed me!
Also, there's probably some fussy issues with the embedded image in the pdf, and maybe its representation in the file. Try blurring it just a bit, changing jpg quality, upsizing it, or resizing it, using imagemagick or your editor of choice?
There's lots of tutorials on this:
https://www.lifewire.com/remove-moire-patterns-from-scanned-photos-1700238
posted by sebastienbailard at 11:07 PM on April 25, 2020
A moire effect is the result of two overlapping grids, say the gridlike features in your image and then the gridlike display of your viewing apparatus. Where the spacing of grids is intrinsically important. For two different viewing apparatuses, two different effects. The web browser representation (and laptop screen) has one spacing, the final printed book will have another, some image viewing application has another. If you think of your pdf viewer and printer as a traditional moire effect with grids printed on plastic sheets, you're essentially swapping in a different plastic sheet with hugely grid spacing and noticing the effect goes away. Or maybe swapping both sheets at once.
> The PDF needs to be viewed by a client online, but eventually will be printed in a book. Google-fu has failed me!
Also, there's probably some fussy issues with the embedded image in the pdf, and maybe its representation in the file. Try blurring it just a bit, changing jpg quality, upsizing it, or resizing it, using imagemagick or your editor of choice?
There's lots of tutorials on this:
https://www.lifewire.com/remove-moire-patterns-from-scanned-photos-1700238
posted by sebastienbailard at 11:07 PM on April 25, 2020
Generally, browser-based PDF viewers are terrible. (I used to be a copyeditor and had to deal with this problem a lot.) If the PDF looks fine in a dedicated viewer (Adobe, Preview, Skim, evince, okular, etc), and it looks fine when printed out, then just ask the client to do use a separate program.
posted by number9dream at 10:51 AM on April 26, 2020
posted by number9dream at 10:51 AM on April 26, 2020
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posted by RichardP at 10:57 PM on April 25, 2020 [2 favorites]