how to skip attributes/key in JSON output

[xxxazxxx]

Images Model contain id, file_name and description.

The usual output is :
{
"images": [
{
"id": 48660,
"file_name": "9e0f6.jpg",
"description": "View 1"
},
{
"id": 48665,
"file_name": "fd42f.jpg",
"description": "View 2"
},
{
"id": 48662,
"file_name": "477e8.jpg",
"description": "View 3"
}
]
}

How do I remove the attributes/keys and convert the values to an array?
{
"images":[
[
48660,
"9e0f6.jpg",
"View 1"
],
[
48665,
"fd42f.jpg",
"View 2"
],
[
48662,
"477e8.jpg",
"View 3"
]
]
}

Fomatted output : http://www.privatepaste.com/bb43a86891