To get chart's JSON, use the command report/render_json:

svc=report/render_json&params={"attachmentIndex":<uint>,
			       "width":<uint>,
			       "useCrop":<uint>,
			       "cropBegin":<uint>,
			       "cropEnd":<uint>}

{
    "datasets":{		/* data */
        <text>:{		/* chart's index */
            "name":<text>,	/* chart's name */
            "color":<uint>,	/* line color */
            "y_axis":<uint>,	/* use second y axis (for splitted charts with different measurements): 0 -no, 1 - yes */
            "data": {
                "x": [
                    <uint>,	/* chart's trace (time) */
                    ...
                ],
                "y": [		/* chart's trace (value) */
                    <int>,
                   ...
                ]
            },
            "colors": [		/* chart's color intervals */
 
            	[<uint>,	/* interval start time */
            	 <uint>],	/* color */
            	...
	    ],
        },
        ...
    },
    "markers":[			/* markers */
        {
            "type":<uint>,	/* type */
            "x": [		
                <uint>,		/* time */
                ...		
            ]
        },
       ...
    ],
    "background_regions": [    /* backround intervals */
        {
            "name":<text>,	/* name */
            "color":<uint>,	/* color */
            "priority":<uint>,	/* priority */
            "regions":[	
                [<uint>,	/* interval start time */
                 <uint>		/* interval end time */
                 ],
                ...
            ]
        },
        ...
    ]
}