*3.4. Visual Analysis*

The first step in analyzing the obtained data was by performing image subtraction to visually assess how much change occurred between different time points. This approach showed no information close to the solar disk because of image saturation, and a neutral density filter was used to try and reduce the saturation problem. This did reduce the saturated area, but there was still no visible information regarding the ramp events. Figure 6 shows the result of the image subtraction with the saturated region highlighted.

In the case of image subtraction, since both images had a similar saturated region, the result after subtraction are black regions in the image. On Figure 6 the rightmost image has a smaller saturated region due to the use of the neutral density filter. Since a visual analysis was not sufficient to determine whether the data obtained were useable for modeling purposes, the next step was to perform a linear correlation analysis from image features and power data.

**Figure 6.** Image subtraction examples with the solar region highlighted. (**a**) Before installing the neutral density filter and (**b**) after installation.
