## 2 Literature Review
### Combining the Geometries
#### 2.3.4 Confocal Microscopy with a Detector Array  
We have already mentioned that the spinning disk confocal microscope has an array of detector pinholes [56], whereas a point-scanning confocal microscope uses just a single detector pinhole. Many papers have discussed replacing the pinhole of the confocal microscope with a detector array. [PERSON] and [PERSON] proposed using a detector array to give multiple images that were then digitally deconvolved [90]. [PERSON] et al. used a detector array to measure the spread light distribution while scanning [91]. They observed shifts of the main maxima and sensitive behaviour of the side lobes in the image and claimed that these could be used to extract more information. They called tracking the maximum in the detector plane a Type III microscope, in contrast to a Type I microscope (nonconfocal scanning) or Type II microscope (confocal microscope). This approach could be useful in confocal transmission microscopy, where the confocal spot may be deflected by refractive index inhomogeneities in the object. [PERSON] and [PERSON] investigated the image of an edge formed by the maximum signal [92]. They calculated the image of the edge in the detector plane, showing that the PSF is distorted. They found the intensity at the edge itself for confocal microscopes with a finite-sized pinhole or slit. [PERSON] and [PERSON] investigated using a detector array to enhance resolution [93]. A detector array can also be used to align the confocal pinhole or to adjust its size post-imaging [94; 95]. [PERSON] described a system using multi-point illumination and a detector array [96]. The image from the detector consists of sub-images from each illumination spot. He called their system video confocal microscopy [97]. Different images can be reconstructed by averaging or determining the maximum or minimum value in the sub-image. He also proposed super-confocal imaging, defined as \(max+min-2 avg\), which exhibits exceptional optical sectioning characteristics. More recently, he has applied statistical processing of the sub-images, based on moments, giving impressive results [98]. [PERSON] et al. proposed the technique of focal modulation microscopy, where the illuminating spot is modulated spatiotemporally, and the signal, after passing through a pinhole, is detected by a lock-in amplifier [99]. The illumination consists of fringes modulating an Airy disk, so it resembles a scanning version of SIM, where the phase of the fringes continuously varies in time. The aim was originally to improve penetration of a scattering object, but it was found that the transverse resolution was also improved [100]. [PERSON] et al. proposed a system with spatiotemporal modulation [101]. One scheme was called scanning patterned illumination (SPIN) microscopy and employs the modulation of the excitation combined with temporally cumulative imaging by a nondescanned array detector. The second scheme, scanning patterned detection (SPADE) microscopy, used the modulation of the detected signal together with spatially cumulative imaging by a nondescanned single-element detector. [PERSON] et al. proposed spatiotemporal modulation by mathematical processing of digital images, which they called virtually structured detection (VSD) [102]. [PERSON] et al. explored resolution enhancement in nonlinear scanning microscopy by saturated absorption or stimulated emission through post-detection digital computation [103]. Many papers have explored the technique of subtractive microscopy, where the signals from two different pinhole sizes are subtracted to give an improvement in resolution [104; 105; 106; 107; 108]. Usually, subtraction is detrimental, however, because it tends to decrease the signal while also increasing the noise. This problem can be avoided by using a ring-shaped detector array rather than subtracting [104]. Further, the OTF for confocal fluorescence with a finite-sized pinhole exhibits negative regions [72], so subtraction actually increases the signal [105]. [PERSON] et al.