## 4 Results  
During sapphire growth in the Ky method, images were acquired from the melt surface of the alumina material using the proposed system, and the coordinates of the stream-line center were processed through an image processing algorithm. After the melt material caused convection and before it was stabilized, 10 images were acquired at 5 min intervals. Figure 10 shows four representative images among the 10 images that resulted from the calculation using the algorithm. To determine the reliability of the image processing results, the island positions (shown by a green triangle) were compared with the central point positions of stream lines detected through the developed algorithm (shown by a red circle) in the figures. The black regions obtained from image preprocessing represent the data of stream-line areas, which had low temperatures in the original image. Noise elements are generated in certain regions (see Figure 11) from the stream-line, depicted as black dots. This is one problem associated with image binarization. These noise elements are generated from the results of binarization using regional threshold values. Most noise can be removed by a low-pass filter and by removing pixels under a certain pixel value. However, large black regions are not removed, as shown in the Figure 11. When these noise elements are calculated together with other stream-line elements in the Hough transform, unintended straight lines may be generated, causing a problem in the calculation of intersection points. Yet such unremoved shades are not a serious concern when detecting the center point of the island because their intersection count is smaller than that of the actual stream-line elements. Also, they do not appear as main straight lines on the \(\varrho\)-\(\theta\) coordinate system. When the observed and detected islands were compared, in most cases, the coordinates of two points were on the main stream lines, but coordinate errors occurred according to the shape of the stream-line intersection positions. When stream lines intersected in the shape of a straight line, there was about a 7-pixel (approximately 0.7 mm) error for the island coordinates. However, when the stream lines intersected in a vortex shape, as shown in Figure 12, a maximum error of 13.93 pixels (approximately 1.4 mm) occurred in the distance between the actually observed coordinates and the coordinates obtained from the algorithm. Figure 9: Flowchart of the auto-seeding process. Figure 10: Image processing results of the melt surface. (**Red**: island position, **Green**: position of image processing result). Ten images were acquired from the time the surface began to melt inside the growth furnace. The positions for the center point of the island as observed and as detected through the image processing algorithm are shown in Figure 13. Table 2 shows the coordinates of the island as observed and as detected from the algorithm, as well as the distance between the coordinates in pixels. The difference ranged from 6.32 pixels (at the minimum) to 34 pixels (maximum), and the average difference was 18.76 pixels, which is about 1.9 mm in actual distance. One explanation for these differences between the two coordinate values is because the stream-line information at the center of the image was lost: about 25% of the region visible through the view point is occupied by the shape of the rod and seed, as shown in Figure 14, resulting in lower accuracy. Figure 11: Noise elements after image preprocessing. Figure 12: Error detection at the curved parts of stream lines. (**Red**: island position, **green**: position of image processing result). In general, the internal convection of the melt material was stabilized after about 20 h in the heating process, and the center position of the island in the melt material is within 10 mm of the center of the crucible in the growth furnace. After that, when the island size grows to 10-20 mm, the seed is lowered.