Image has swirled pixels when exported for internet

[Sheila Finch]

When I resize to 1500px jpg and change ICC profile to sRGB IEC61966-2.1 the painting has swirled pixels. This is only happening for the images of the sides of the painting. (not images facing straight-on) Weird. I turned off accelerator.I'm running on macOS M1 Max Ventura Version 13.6

[lacerto]

It is the canvas of the painting when changing the resolution, and probably combined with JPG compression artifacts that causes the behavior. You might be able to alleviate the problem by using a bit different resampling size, method and then saving to PNG. if nothing else helps, the parts showing most moiré can be tried to be blurred a bit, but it is tricky because this is a painting and changes are easily too big, or uniform, and you are supposed to keep all details (for this reason e.g. cloning non-moiré parts might be impossible). But see if simply just using a different resolution, resampling method and no JPG compression could make a change. 

[markw]

You could also try changing your Resample method from 'Bilinear' to 'Lanczos 3 (non-separable)' in the Export dialog, that may help a bit too.

[Sheila Finch]

Thank you lacerto and markw for your suggestions. I tried them all, with no success in fixing the moire in the images. 

I ended up using the Mac-installed app: PREVIEW to change the image size to 1500 px. Then I imported it to Affinity Photo, adjusted the light and warmth, and then exported. The image looks perfect. No moire.

I'm a little flabbergasted that I had to use macIOS Preview app resizing tool to successfully change the image size before importing to Affinity Photo. Could this be a bug?

[markw]

To be honest I’m surprised too that Preview out performed APhoto!
If you have any or could make some specific test images showing this problem that you could post here it might help with finding a way forwards using APhoto.
But glad you found a workable solution for now.

[lepr]

1 hour ago, Sheila Finch said:

ended up using the Mac-installed app: PREVIEW

To emulate Preview resizing in Affinity Photo:

1. open an image file in Affinity Photo
2. document convert format to RGB/32
3. document resize with 'Lanczos 3 (separable)' resampling
4. document convert format back to original (for example, RGB/16 or RGB/8)

 

[Sheila Finch]

lepr, thank you. I followed the steps you suggested to emulate Preview and remove the moire, but the moire remains in the image. This is the image after exporting at 1500 px resizing as a jpg. I guess I'll just use Preview first if this ever happens again. This is actually the first time I've had this happen, so I wonder if something in the recent Affinity update might have been changed. Oh well, at least I have a solution.

[lepr]

52 minutes ago, Sheila Finch said:

but the moire remains in the image.

If you upload the full size image (preferably inside a zip file), I'll see what I can do with it in Affinity.

Edited October 25, 2023 by lepr

[Sheila Finch]

Lepr, thank you for offering to take a look at the image!

Again, the moire shows up when the image is reduced to 1500 px. Here's the image attached.

4121 right test.jpg.zip

[markw]

@Sheila Finch This is interesting, I’m not getting the same moire effect as you.
Here are the Export settings I used and the result.
Can you post your Export settings?

[Old Bruce]

This is a combination of the Pixels in the JPEG making a moire with the Pixels on your screen. View it at less than 100% and you'll see it. Could also be a moire from the texture of the canvas.

[lepr]

6 hours ago, Sheila Finch said:

Again, the moire shows up when the image is reduced to 1500 px. Here's the image attached.

No moire is produced when resizing that image to 1500 px with Lanczos or bicubic resampling.

Perhaps you are being misled by Affinity's display which is compromised by using mipmaps and a choice of bilinear (view quality = 'Best') or nearest neighbour (view quality = 'Fastest') resampling, whereas Preview's display uses either bicubic or Lanczos resampling.

Edited October 26, 2023 by lepr

[John Rostron]

I have also tried this, resizing to 1500px, Lanczos, and see no moire at any view magnification between 25% and 400%.

John

[Sheila Finch]

Thank you all for your help on this!

I followed your guidance again today, carefully following the steps, and low-and-behold, today the moire is gone when I change the resampling to either of the lanczos settings or using bilinear! 

I can only assume I screwed up following the export settings. Both of the painting side images looks just fine now!

Thank you lepr, markw,  old bruce and john!

[lepr]

2 hours ago, Sheila Finch said:

bilinear

Bilinear will produce moire with your image. You probably meant to write bicubic.

 

[Sheila Finch]

Yes! Thank you Lepr. Didn't realize I wrote bilinear.