Hi Clemens,
Thank you for using Syncfusion controls.
We are not clear with your requirement. Can you please provide below details?
1. Do you want filtering the GridImageColumn based on image size?
2. Filtering needs to do with in SfDataGrid itself or Excel?
It will be helpful for us to check on it and provide you the solution at the earliest.
We unable to run your test application we are facing the below exception.
Please provide the runnable sample, otherwise we will create it by own.
Regards,
Susmitha S