Objects in an image can have different relationships. For example, objects can be coordinated, where their coordinates have the same value, the same focus, and thus they are seen from the same perspective. Distance is also important when dealing with the viewer’s perspective, as the distance between two objects can vary based on your point of view. Objects can also be parallel when two objects lie on the same plane and are at an equal distance from each other at all times, meaning they will never intersect. The space between two intersecting lines is then defined as an angle, and an object can only be situated at an angle to something else, if it has direction. If two objects are located next to each other and they share a common point, they are defined as tangents. In relations, you will hear the terms negative and positive, which relate to the opposite values such as light and dark. A transparent object is see through, and light can shine through it so other objects behind it become visible. An opaque object is visually impermeable, thus blocking any possible light that can come through. Objects can also be relational to each other when they overlap, where parts of an object can lie on top of another object. When the objects overlap and look to be one object, they are then called a compound form. Subtraction occurs when the part of the object that overlaps another is deducted from the underlying object. Other relational occurrences between objects include penetration, extrusion, influence, modification, and variation.
Today in design, transparency has become a very popular tool. Specifically in web design, product developers are loving this trendy technique. Transparency can be used for various reasons, such as adding quality or character to your design. Transparency, being the opposite of opaque, allows us to see what is underneath. In this way, transparency it can be used to create depth and visual interest in your design. It is often used for header pieces, as well as images that are overlapping one another. Transparency can also be used to put text over an image, to make the text readable. The use of transparency can create a layering effect to your design, and can bring out and obvious figure and ground. The use of transparency can be subtle or very obvious, but in both cases can be a major design element. Transparency can also create contrast, especially in the foreground and background. It is also a great tool to use in order to maximize your space, as you can layer things on top of one another. In web design transparency is great in navigator bars, drop down menus, or sidebars. If you feel like your design may be lacking, transparency may be just what you need to enhance your design.

This image shows a great example of transparency. The different colored shapes overlap the images, adding visual interest and also adding space for the text, while also making it readable.

The transparency in this image is simple, yet effective. It creates a clear headline, but you can still see a bit of the image popping through. This way there isn’t a huge color block in the center of the page, which could distract your eye.

This poster has a very obvious use of transparency. However, it is effective as it relates to the meaning of the piece. The letters all spell out typography, making it very clever when we finally notice that.

This poster also shows an obvious use of transparency, used to create visual interest in the image. If it weren’t transparent, it would have blocked out too much of the image. However with using transparency, we see the cool effect of the shapes and lines, while also still enjoying the image beneath.
Sources:
http://www.designworklife.com/2011/07/12/foreign-policy-design-group-%C2%BB-13-wives/
http://designmodo.com/transparency-website-design/
http://spyrestudios.com/40-great-examples-of-transparency-in-website-design/
http://www.vandelaydesign.com/transparency/
http://www.thedesignwork.com/beautiful-typography-poster/
http://www.graphic-exchange.com/archives/04cd-12.htm