A forage harvester, comprising: a chopper that receives severed crop and chops it into pieces; a kernel processing unit that includes a first kernel processing roller and a second kernel processing roller separated from the first kernel processing roller by a gap; a first drive mechanism driving rotation of the first kernel processing roller; a second drive mechanism driving rotation of the second kernel processing roller; an imaging device configured to capture an image of processed crop that has been processed by the kernel processing unit, the image indicating kernel fragment radiation fluoresced by kernel fragments in the processed crop; an image processing system configured to identify sizes of the kernel fragments in the image based on the indication of kernel fragment radiation fluoresced by the kernel fragments; and a control system that is configured (a) to generate a control signal to control the first drive mechanism to control a speed differential between the first and second kernel processing rollers (118, 120) based on the identified sizes of the kernel fragments and/or (b) to generate a gap control signal to control a roller position actuator that is configured to drive movement of one of the first and second kernel processing rollers (118, 120) relative to another of the first and second kernel processing rollers (118, 120) to change a size of the gap, such that the roller position actuator is configured to change the size of the gap based on the identified sizes of the kernel fragments; characterized by comprising a radiation source configured to emit source radiation at a source wavelength that causes the kernel fragments in the processed crop to fluoresce the kernel fragment radiation at a fluoresced wavelength; by a radiation source controller configured to control the radiation source to emit the source radiation, and by a notch filter configured to be optically disposed between the imaging device and the kernel fragments in the processed crop and configured to filter radiation outside a range of wavelengths that is centered on the fluoresced wavelength. a chopper that receives severed crop and chops it into pieces; a kernel processing unit that includes a first kernel processing roller and a second kernel processing roller separated from the first kernel processing roller by a gap; a first drive mechanism driving rotation of the first kernel processing roller; a second drive mechanism driving rotation of the second kernel processing roller; an imaging device configured to capture an image of processed crop that has been processed by the kernel processing unit, the image indicating kernel fragment radiation fluoresced by kernel fragments in the processed crop; an image processing system configured to identify sizes of the kernel fragments in the image based on the indication of kernel fragment radiation fluoresced by the kernel fragments; and a control system that is configured (a) to generate a control signal to control the first drive mechanism to control a speed differential between the first and second kernel processing rollers (118, 120) based on the identified sizes of the kernel fragments and/or (b) to generate a gap control signal to control a roller position actuator that is configured to drive movement of one of the first and second kernel processing rollers (118, 120) relative to another of the first and second kernel processing rollers (118, 120) to change a size of the gap, such that the roller position actuator is configured to change the size of the gap based on the identified sizes of the kernel fragments; characterized by comprising a radiation source configured to emit source radiation at a source wavelength that causes the kernel fragments in the processed crop to fluoresce the kernel fragment radiation at a fluoresced wavelength; by a radiation source controller configured to control the radiation source to emit the source radiation, and by a notch filter configured to be optically disposed between the imaging device and the kernel fragments in the processed crop and configured to filter radiation outside a range of wavelengths that is centered on the fluoresced wavelength.