faulty resampling result at the right edge for small scaled images in exported pdf

[c.pfaffenbichler]

For pixel-images that are placed at a small scale and have certain detail near the edges the resampling result at the right edge appears to be faulty – namely a duplicated row of pixels. 

Adding space to the image will get the expected result. 

The screenshot shows the two images open in Photoshop (original dimensions 2048px x 2048px and 2148px x 2148px) and in the background the exported pdf from an indd in which they were placed at 5%. 

I suspect this may have come up before, but I couldn’t locate a pertinent thread. 

Anyway, thanks in advance for any insights on this. 

[Willi Adelberger]

I would consider this as a bug. 
in this case i would recommend a workaround. Put the form into an elliptic image frame to mask away that erratic pixels. 

[rob day]

Hi @c.pfaffenbichler , This has come up before, usually with icon art. It can happen when there are no pixels outside of the edge to sample from on the requested down sample. The solution, as you are showing is to include some padding.

https://community.adobe.com/t5/indesign-discussions/edges-of-images-distorting-on-pdf-export/m-p/138...

[James Gifford—NitroPress]

Wasn't there also a factor of this happening (more often) with PNG rather than JPEG?

[c.pfaffenbichler]

In my test transparency/flat did not make a discernable difference. 

[c.pfaffenbichler]

Thank you both for the feedback. 

[Brad @ Roaring Mouse]

Yes, it has come up before. It's an unfortunate side-effect of Bicubic Downsampling. The short answer to why is that in order for it to work, Bicubic requires a certain grid of pixels to sample to create each pixel in the reduced image. If it doesn't have all it needs on the right and bottom edge, it repeats the last available column or row until it does. So depending on exactly what size (dimension) you are reducing to, the effect may be barely noticeable or REALLY noticeable, and our perception depends on what content is in the image. If these had been full photos, you might not even notice it. How to fix? Try Average Downsampling in your PDF export nstead. You might lose a bit of smoothness, but it will handle these outer edges better.

[c.pfaffenbichler]

I am afraid that may not be all there is to it. 

Bicubic Downsampling to 5% in Photoshop gets the left result, Indesign the right: 

[James Gifford—NitroPress]

InDesign's implementation is different and not as 'intelligent' about these details. That's the case for many features where a primary (focused) app does a better job than InDesign's equivalent feature.

[Brad @ Roaring Mouse]

I agree that's there's a flaw in InDesign's application of bicubic interpolation here. It personally find it's more appropriate for enlargements.

Illustrator also creates these edge artifacts, but minimally; nowhere near as prominent.

[rob day]

The difference might be InDesign is applying JPEG compression along with the downsample on Export. I think if you want to compare, in Photoshop you would have to downsample, save a JPEG with a similar compression quality, close and reopen.

[Brad @ Roaring Mouse]

Doesn't matter. The artifact occurs even without compression.

As I mentioned, it happens on a full image as well. There's a dupicate column of pixels down the right side. Not as noticeable as with the circle shape, but definitely there.

 

[Brad @ Roaring Mouse · Accepted solution]

No matter the scale of the image, there's always one exact extra column of duplicate/near duplicate pixels at each size on the right edge.

[rob day]

This is what I get with CC2021 :

[Brad @ Roaring Mouse]

I started a bug report on User Voice (surprisingly, noone has posted it before as far as I could find), so if anyone wants to upvote this or add anything, here's the post:

https://indesign.uservoice.com/forums/601180-adobe-indesign-bugs/suggestions/47496800-bicubic-downsa...