Json output is not right

I have in EE a json file that pull the file name ([email protected]) from de database where the name is ok but the output is file_name%402x.jpg

how can I fix that?

{exp:channel:entries channel="json" disable="member_data|paginate" dynamic="off" orderby="hotspot" sort="decs" category="3"}{
    "id": {entry_id},
    "foto_groot": "{foto_groot}{file_name}{/foto_groot}",
    "titel": "{title}",
    "url_ext": "{url}",
    "url_int": "{url_title_path=/}",
    "categorie": "{categories}{category_name}{/categories}",
    {if {current_time format="%U"} - {entry_date format="%U"} < '2500000'}"flagsn":{"nieuw":true },{/if}
    "flags":{"new":{hotspot}} }{if count==total_results}{if:else},{/if}{/exp:channel:entries}
]
}