Unable to get image in SP list smaller (JSON format)

Hi,

I have a list of which the items are supplied by a powerapp. For a column that should show an image the powerapps supplies the url and the the column is formatted using JSON. The image jpg file is in a sharepoint document library.

{
  "$schema": "https://developer.microsoft.com/json-schemas/sp/v2/column-formatting.schema.json",
  "elmType": "img",
  "style": {
    "background-color": "none",
    "width": "50px",
    "height": "50px"
  },
  "attributes": {
    "src": "@currentField"
  }
}

I would now want to make the image smaller. If I change both height and width to "25px" the image just gets 50% narrower, height stays the same (narrowing the image) . Also editing the underlying jpg file to half the size doesn't solve this, the image just gets coarser (due to less pixels/same size).
How can I solve this?