What does it all mean a, b, H (a), H (b). and Explain to me the third step

The original peak point disappears. 3000 2500 1500 1000 500 50 100 150 200 250 Fig. 3. Histogram of the marked Lena image. I) Pseudocode Embedding Algorithm With One Pair of Max imum and Minimum Points: For an M N image, each pixel grayscale value r [0, 25] 1) Generate its histogram H(x) 2) In the histogram H(x), find the maximum point h(a) a e [o, 255] and the minimum point zero h(b)b E [0, 255] 3) If the minimum point h(b) > 0, recode the coordinate (i,j) of those pixels and the pixel grayscale valueb as overhead bookkeeping information (referred to as over head information for short). Then set h(b) = 0 4) Without loss of generality, assumea