OpenGL is the most widely-used open graphics standard in the world, in fact it is also used by Processing. Processing is a creative coding environment. It can be used for many things, not only drawing (but also sound, network and a hundred other things). So they are two different things, with different goals and different audiences. To a certain extent this makes the comparison of apples and oranges.
Processing is (also) aimed at non-programmers, artists, designers, students etc., it has a very low barrier of entry. Very little code, can generate results. So it's easy and good for rapid prototyping. Not many people go without programming knowledge immediately to using direct opengl calls, however of course that is possible for some.
Processing is a wrapper for a lot of OpenGL and GLSL functionality. It provides an API to quickly and easily use both of these. If you were to do it in OpenGL, you would need more code, than with Processing. Processing hides some of the complexities behind the scenes. The upside is that you don't need to worry about them. The downside is that you haven't learned the ultimate source and so you are dependent on other developers.
Some purists may say that it is "better" to learn and use OpenGL calls directly, instead of learning and using wrappers aka creative coding frameworks (such as Processing, OpenFrameworks and Cinder). However many people want to create rather than have deep knowledge of OpenGL etc. It's a bit related to writing code from scratch or using existing libraries. If you want to do it yourself and learn, you might write everything yourself. If you want fast and tested results, you might use existing code.
So Processing actually uses OpenGL itself for it's P2D and P3D renderers. In addition it has a JAVA2D and a PDF renderer.
In general, a comparison should usually have some frame of reference about skill level, knowledge, goals, time frame etc. Otherwise there can be no effective comparison.
I think a language like OpenGL makes your life difficult in the beginning and easy after a few years. Processing is the other way around. It makes everything easy at start. And after a few years when you get more experienced
Answers
OpenGL is the most widely-used open graphics standard in the world, in fact it is also used by Processing. Processing is a creative coding environment. It can be used for many things, not only drawing (but also sound, network and a hundred other things). So they are two different things, with different goals and different audiences. To a certain extent this makes the comparison of apples and oranges.
Processing is (also) aimed at non-programmers, artists, designers, students etc., it has a very low barrier of entry. Very little code, can generate results. So it's easy and good for rapid prototyping. Not many people go without programming knowledge immediately to using direct opengl calls, however of course that is possible for some.
Processing is a wrapper for a lot of OpenGL and GLSL functionality. It provides an API to quickly and easily use both of these. If you were to do it in OpenGL, you would need more code, than with Processing. Processing hides some of the complexities behind the scenes. The upside is that you don't need to worry about them. The downside is that you haven't learned the ultimate source and so you are dependent on other developers.
Some purists may say that it is "better" to learn and use OpenGL calls directly, instead of learning and using wrappers aka creative coding frameworks (such as Processing, OpenFrameworks and Cinder). However many people want to create rather than have deep knowledge of OpenGL etc. It's a bit related to writing code from scratch or using existing libraries. If you want to do it yourself and learn, you might write everything yourself. If you want fast and tested results, you might use existing code.
So Processing actually uses OpenGL itself for it's P2D and P3D renderers. In addition it has a JAVA2D and a PDF renderer.
In general, a comparison should usually have some frame of reference about skill level, knowledge, goals, time frame etc. Otherwise there can be no effective comparison.
I think a language like OpenGL makes your life difficult in the beginning and easy after a few years. Processing is the other way around. It makes everything easy at start. And after a few years when you get more experienced