Kuromasu by Salih Alan
or solve online (using our beta test of Penpa-Edit tools; use tab to shift between shading mode and the linex mode where left click+drag draws lines and right click marks X’s)
Author/Opus: This is the 20th puzzle from guest contributor Salih Alan.
Rules: Shade some empty cells black so that each number indicates the total count of white cells connected vertically and horizontally to that number including the numbered cell itself. Black cells cannot share an edge, and all white cells must belong to a single connected group.
Also see this example:
Difficulty: 2.5 stars
Time Standards (highlight to view): Grandmaster = 2:00, Master = 3:30, Expert = 7:00
Solution: PDF and solving video.
Note: Follow this link for more Kuromasu puzzles. More Kuromasu can be found in Grandmaster Puzzles Quarterly Vol. 3.