Moiré Effect

On some of the more high quality scans I’ve been downloading and viewing on Panel, I’ve noticed that the screentones show up strangely and create visually disturbing lines and dots. I looked it up and it’s called the moiré effect. I was wondering if anyone else had experienced this and if they have (or even if they haven’t), if they know of anyway to fix this issue. Thanks! Below is an image of a page I was getting the effect on for reference.image|231x500

I’m seeing the same thing, it’s happening with one of my super-hi-res art collections where the image is manga grayscale or black and white, and the vertical resolution is 4900px.

With “normal” 3200px height manga (still hi-res) I’m not seeing the issue.

It’s much less pronounced on a big iPad like the 12.9" but on an iPad Mini (my on the go one) it’s very pronounced. If I pinch-shrink the images I can definitely see the same effect on the iPad Pro.

@Jung could you share one of those files with us. We’re happy to look into it and see if there’s something we can do.

Sure thing, how could I share this with you?

Could you send it to ? A download link also works (Google Drive, Dropbox, Mega, WeTransfer… ).

I sent in an example titled appropriately

After analyzing the file you sent us, we now understand what’s going on.

What you’re seeing is not a Moire Effect. It’s just dithering, a technique used to reduce the amount of information required to represent an image (or other kinds of digitalization).

This is not a bug in the app. Actually, if you open one of those images with Preview on Mac, you’ll get exactly the same result. (see image attached)

When the dither used on an image is ordered dithered, there are some image filters that you can apply (like Inverse Halftoning) to transform the dithered sections into grayscale gradients. Here’s a paper explaining the process

If you’re getting the same file better rendered using a different app, it’s very likely that they are detecting that the image is dithered, and they are applying filters to soften the dither.

We’ll add it to our backlog as a feature request, and look into implementing a good solution in the future.

I hope that makes sense.

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