Left: MIRI MRS detector image of the spatially extended source NGC 7027 for the long wavelength detector MIRIFULONG, sub-band A, after slope fitting (level 1 ‘rate’ output of the JWST calibration pipeline). Spectral bands 4A and 3A are on the left and right hand sides, respectively, each with its own colour scale indicated at the top. The two half-detectors are split for clarity. Fringes appear along the dispersion (vertical) direction. The two spatial coordinates are illustrated: α varies within each slice perpendicularly to the slice as indicated by the arrow, β is constant for each slice with i and j denoting the slice number. The conspicuous bright features at specific wavelengths (that appear along the horizontal, spatial direction) are bright emission lines from the source. Right: same image after division by the fringe flat derived from that source, with the same colour scales as in the left panel. Fringes are largely suppressed.