The three images shown were blurred using square averaging masks of sizes n = 23, 25, and...

The three images shown were blurred using square averaging masks of sizes n = 23, 25, and 45, respectively. The vertical bars on the left lower part of (a) and (c) are blurred, but a clear separation exists between them. However, the bars have merged in image (b), in spite of the fact that the mask that produced this image is significantly smaller than the mask that produced image (c). Explain the reason for this.