In Dolphin, you can increase the internal resolution from native (640x528) to 1080p (3x Native) or even 4K (6x Native) . This significantly reduces jagged edges and makes the environment appear much sharper.
Because Black Ops was one of the most demanding titles on the Wii, it often suffers from "hiccups" or frame drops during emulation. Use these settings to stabilize quality: wii call of duty black ops rom extra quality
You can download community-created HD Texture Packs that replace low-resolution original assets with high-detail images. These are installed by placing the texture folder into Dolphin’s /Load/Textures/ directory. In Dolphin, you can increase the internal resolution