def herschel_to_mJy_per_pix(image, band):
    """Converts units from Herschel photometric images (PACS and SPIRE) from Jy
    per pixel to mJy per pixel.

        Inputs
            image: Herschel image in Jy/pix units

        Output:
            image: Herschel converted to  mJy/pix units
    """

    # from Jy to mJy
    image_mJy = image[0].data * 1e3

    # factor to update phometry
    # conv_factor = {70:1.05, 100:1.08, 160:1.0, 250:.92, 350:0.95, 500:0.84}
    # image_mJy *= conv_factor[band]

    image[0].data = image_mJy

    # update header
    image[0].header['BUNIT'] = 'mJy/pixel'
    image[0].header['history'] = 'units converted to  mJy/pixel'

    return image