Digital Art (a.k.a. Computer Art) emcompases a large number of different expresion vehicles with the common denominator of using a computer as the main tool.
Digital Photography is probably the most popular use of computers in art. It includes: Photography taken with digital camera, computers used as a digital darkroom, post-processing of images in a digital environment and adding or combining imagery producing a digital collage. If you want to capture reality, a digital darkroom allows the same corrections that a real darkroom provides and more. With the current software tools available, it is also possible to enhance and even alter reality. I personally enjoy creating surreal worlds, but I believe that there is a fine line in the use of computers to alter reality, because it is possible to create lies too...
Digital Painting and digital drawing
Current software packages are extremely sophisticated. They can simulate different types of brushes or pencils, pressure and angle of those utensilts, paint type and canvas materials. At the same time, there is software that actually paints automatically even simulating the Masters' styles. This ambiguity poses a special challenge to digital painters, who have to contest the perception that digital painting is easy...
It seems that in Generative Art computer programs create interesting imagery by themselves. In reality, a true generative artist imagines the final result and programs a software code to create it. On the other hand, there is commercial software that can produce generative art, so generative artists also face the difficulties of differentiating themselves.
Algorithm Assited Digital Art
Also called Math Assited Art, utilizes mathematical equations (algorithms) to create or modify the images. Commonly known algorithms used in Digital Photography are blurring, sharpening and hue adjustments. But other algorithms can allow image transformations beyond the real domain opening the gates of imagination.
3D Digital Art
The designation of '3D Art' is used in many disciplines ranging from 3D projection to game animation. The tools, skills and objectives of these disciplines are quite varied.
3D Projection adds depth perception to plain two dimensional images.
3D animation creates imaginary characters that become to life through computer models that mimic real life (Mostly in Games and Movies.)
3D Stills (which I prefer to call Virtual Photography) mimics photography as it takes simulated computer characters and combines them in a relistic or surreal landscape.
3D modeling focuses on the creation of the characters and props used in 3D animation and stills.