function metis_flat_field, data, header, cal_pack, error = error, quality_matrix = quality_matrix, history = history

	journal, 'Flat-field correction:'

	if header.filter.contains('VL', /fold) then begin
		ff_info = cal_pack.vl_channel.flat_field

		ff_image = readfits(cal_pack.path + ff_info.file_name, /silent)
		ff_error = readfits(cal_pack.path + ff_info.file_name, exten_no = 1, /silent)
		ff_file = ff_info.file_name

		first_row = header.ref_rows eq 'Included' ? 2 : 0
		detector_size = cal_pack.vl_channel.detector_size.value
		ff_image = ff_image[*, first_row : first_row + detector_size - 1]
		ff_error = ff_error[*, first_row : first_row + detector_size - 1]

		journal, '  VL ref. rows = ' + header.ref_rows.tolower()
	endif

	if header.filter.contains('UV', /fold) then begin
		ff_info = cal_pack.uv_channel.flat_field

		i = where(ff_info.nbin eq sqrt(header.nbin))
		ff_image = readfits(cal_pack.path + ff_info[i].file_name, /silent)
		
		; WARN - flat field for the uv channel must still be provided
		
		ff_error = ff_image * 0.
		ff_file = ff_info[i].file_name
	endif

	; WARN - error for binning must be checked
	
	ff_nobin = ff_image
	ff_image = rebin(ff_image, header.naxis1, header.naxis2)
	ff_error = ff_image * sqrt(rebin((ff_error/ff_nobin)^2, header.naxis1, header.naxis2)/header.nbin)
	
	mask = where(ff_image le 0.)
	ff_image[mask] = 1.
	data = data/ff_image
	data[mask] = 0.

	if isa(error) then error += (ff_error/ff_image)^2

	if ~ isa(history) then history = !null
	history = [history, 'Flat-field correction: ', '  ' + ff_file]

	journal, '  flat-field file = ' + ff_file

	return, data
end