## 3 Results  
### OCT Images  
Figure 3 shows the OCT B-Scan images obtained for each panel. For Indus silver and Mauritius blue, the images from both LF-OCT and FF-OCT systems are compared. Both instruments give similar images, showing a larger optical thickness for the clear coating on the blue panel. Both instruments also show similar trends in the differences in appearance of the second layer of the two samples. Within the second layers, the signal contrast between the bright flakes and points in between is lower for the blue panel than the silver panel. To give the blue colour, the blue panel second layer may contain blue pigment particles, which would add to the scattering signal between flakes. The main difference between the images from the two instruments is the lateral resolution. The resolved flakes from the high lateral resolution FF-OCT appear narrower than for the LF-OCT, where the lower lateral resolution has broadened their apparent width. Both (i.e., Barolo and Santorini) black LF-OCT images are significantly different, compared with silver and blue, with the visible base coat thickness being much thinner. The clear coat of Santorini black is the thinnest of all the samples.  
Figure 3: B-Scan images of Indus silver (**a,b**), Mauritius blue (**c,d**), Barolo black (**e**), and Santorini black (**f**) automotive metallic paint samplers. Taken with FF-TD (**a,c**) and LF-FD (**b,d–f**) parallel OCT systems. The FF-OCT B-Scans are taken from within 1 mm of the location of the corresponding LF-OCT images. Scaling is the same for all images. Colour bar units are dB.  
Though the relatively lower lateral resolution of the LF-OCT has partially blurred the second layer, it is still sufficient to resolve the image texture. Figure 4 (top) shows the LF-OCT B-Scan of the silver panel (same as Figure 3b) with two A-Scan locations (red and blue) marked on. Figure 4 (bottom) is the plot of the intensity of these two A-Scans, and the apparent thickness estimated from obvious peaks. Considering these (red and blue) A-Scans separately and without prior knowledge of the sample, as would be the case in a single point measurement, their interpretations give a large difference in the thickness measurement of the clear coat. In this case, for the red A-Scan the apparent signal for the second interface comes from far too deep. No reasonable estimate of the base coat layer could be made without prior knowledge of the A-Scan properties for the sample. In contrast to this lack of information in the 1D single point measurement, in the 2D B-Scan image the layers and their boundaries are immediately visibly apparent without any prior knowledge. In this case the source of the error for the clear coat thickness in the single point measurement is the dominating signal from the metal flakes, which at any given lateral position could be present at any depth within the second layer. For a single point system, to reliably overcome this, the user could take multiple measurements at different sample positions and use the averaged A-scan signal for thickness calculation. However, we will show that reliable coating thickness and uniformity information could be obtained by using the single shot LF-OCT system and automated image segmentation algorithms, without the need for multiple measurements.