A cartoon ninja drawing is a fun way to visualize this legendary profession. Contrary to most media depictions, there is no written evidence that they wear a black garb. Rather, disguising one's self as civilians is the more preferable method of blending in. Therefore, there is a lot of leeway for drawing a ninja cartoon.
Still, for the purposes of getting a common depiction of a ninja that people have been used to seeing in modern media, a black garb is a great start. Additional pieces of armor or clothing can be considered so long as the idea of lightness is emphasized.
Weapons are a great asset. While there are many types of weapons that can be used, such as a katana, kunai, grappling hooks, small knives, darts, shuriken, bows, chain and sickle, etc, there's no need to draw it all. Rather, be selective in the amount of gear.
The other appeal of a ninja are legendary or supernatural abilities like invisibility, flight, splitting into multiple bodies, and hand seals to conjure up magical spells. Though unnecessary, these are definitely things to consider when trying to draw a cool cartoon ninja drawing.
In Photoshop, select a small chalk brush and begin a new layer. The sketch will determine the position and general pose. This is where the amount of weapons will be decided as well as overall looks and proportions.
There can be some silliness with the looks. The goal is to have some fun balancing the seriousness of a ninja with a style of drawing typically known for being simple and aimed at a younger audience. In this sketch, a kunai and katana is used as the main weapon.
Aside from putting in guidelines for the head, a artistic mannequin is used to sketch out the body. For this particular drawing, the ratio from the size of the head to the rest of the body is about 1:1. Different ratios can be used depending on the goal of the illustration.
The pose is depicting a stance ready to attack. Other common poses associated with a ninja can be running, climbing, standing upright, flying, etc. The choice is up to the artist. After the initial sketch is done, it will be used to create a more refined line drawing.
Cleaning up the sketch lines can get meticulous at times. It can get even more so when major areas of the design stage aren't flushed out. Still, there should be enough rough ideas to pull from the original sketch before moving to this stage.
In a more typical cool fashion, the entire head doesn't have to be disguised. It is just enough to put a mask over the bottom part of the face to hide the character's identity. This will also allow for creativity in the character by designing a fitting hairstyle.
For the rest of the body, erase and redraw the sketch lines. Pay extra attention to the overall position. Since it is a black garb, isolate the pants and upper garb. Even using simple lines to isolate the arm and feet region is enough at this stage.
The weapons may take some time to get right as it requires some detailing work. Specifically, straight lines can be done by dotting one area of the canvas, hold 'shift' on the keyboard, and dotting another area to connect the two dots to create a straight line.
Adding color is a simple process. First, create a layer underneath the line art. There is a need to go back and forth between these two layers for speed up the filling process. The tool that is the most helpful here is the magic wand.
Returning to the line layer, use the magic wand to select empty areas like the face. This will create a fill. Next, go back to the layer underneath the line drawing. Then go to Edit > Fill, and select Use: Color. Select a skin color and press OK.
Doing so will fill in the area designated by the wand tool on that layer. Repeat this step for the rest of the body. Please note to check that all the lines are closed off. Leaving any lines open will make the wand tool select an area out of the confines of the drawing.
Luckily, there is only one other color to be filled in: a dark grey for the garb. Also make sure to double check to see most of it is filled in before continuing to the final step. If there are any white spots, draw it in manually. When ready, lock this layer down.
Locking the layer helps prevents and spilling or altering of the ninja shape. In the layers box, look for the word 'Lock' and lock the appropriate section. In this case, it will 'lock transparent pixels'. Other versions of Photoshop may say something different but generally speaking, it's around the same area.
Now, color consists of two distinct brushes. For the face, use a chalk brush first to add in the features of the nose, forehead, and eyes. Switch over to a round brush to smooth out the colors. The hair can be done with the same tools.
The body is a bit more complicated. While the garb is black, it is not a good idea to fill it in completely. Rather, use small brush strokes to indicate folds in the clothes. Use the line drawing as guidelines to separate any major areas.
The sword is simple enough as it just requires a lighter grey to suggest metal. The same can be done for the hands. In other words, rather than draw each individual finger, just dab in areas where the light will hit to signify individual digits.
To finish off the drawing, consider adding an extra layer of light. For example, if the face mask or other areas of the garb is too dark, create a new layer on top of the line drawing layer. Then, draw in some areas of light to flush out some added depth.
And that's pretty much it. From start to finish, it just takes a bit of sketching, refining, and understanding basic coloring concepts to create a simple and cool looking cartoon ninja drawing, holding two weapons, ready to attack.