Compression artifacts in OMERO.iviewer

Hi everyone,

Users in my lab recently pointed out that their binary images were shown with random grey pixels, as can be seen here:

Is there a setting to change the image quality and remove these compression artifacts somehow?
I suppose it’s harder to know, through the web interface, if the user is connected through LAN or remote DSL and adapt the quality accordingly…


There is not currently a setting in the OMERO.web viewers (iviewer or the older default viewer) to adjust the compression level.
However, OMERO.web rendering API does provide the ability to adjust compression.
If you use your browser dev tools and look under the Network tab, filtering for Images, you’ll see the Images being loaded by the viewer. You can click on these and open in a new browser Tab.
The URL can be quite long, but it will contain q=0.9 for the iviewer.
If you edit this to q=1 you should be able to see an improvement (I saved each jpeg and opened in Photoshop to compare).

This doesn’t entirely remove all compression artefacts: The OMERO rendering engine still returns a jpeg. But it would be helpful to know how much of an improvement this is for you?
To fix this entirely, the rendering engine would need a new API which is a much bigger task.

I’ve opened an Issue for iviewer, to allow users to choose the lower compression level:



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Thank you for these details. It looks like setting q=1 is a big improvement as it removes most of the artifacts on binary images. From the few images I’ve taken a look at, q=0.9 puts grey pixels in the white area, and they stand out a lot, whereas q=1 only leaves a few dark grey pixels in the background, which are less easily spotted.

Being able to adjust this parameter from the interface (for example when dealing with binary images) would be perfect I think.

Best regards,


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