Last time we introduced the drawing of sketches , today we will introduce how to use Photshop to express three-dimensionality in a plane. Let's also call it " rendering".
To create the lights for the shark's belly and mouth, I selected the position with the lasso tool and brightened it with the dodge tool. Then trim it with the airbrush tool.
When I finished the greyscale rendering (Fig 1), I created a new layer on top of it and used the greyscale layer for transparency. I filled the layer with color and filled it with blue in the middle. Adjust the saturation until I'm happy with it. 
A faint pink color needs to be attached to the mouth and eyes (Fig 2), and the shark is basically completed (Fig 3).
Use the default 50% medium gray airbrush to blend on the screen to create the shape of the model. Use the same airbrush overlay to create some shadows. Next, where the lights and shadows are created, I start working on details such as eyes, cheeks, wrinkles, etc. Apply the airbrush 3-5 times on top of the large outline. Then paint with an airbrush and insert some highlights. It's a nice and relaxing process, then gradually reduce the opacity of the draft layer while painting the details. I used the path tool to create the teeth. The shark's teeth are arranged in rows, so I had to create them on separate layers and fade the shadows slowly.
This method of adding color (greyscale) is best used on fish. The fish was then rendered using the dodge and burn tools, which also had a nice scaling effect so that the color layer was on top (Figs 3a and 3b above).
In the next section we introduce the drawing of the seabed background .