Graphics in Android

An introduction to how to best integrate and optimize graphical elements within your Android apps: 

Two primary graphics related packages: the android.graphics.drawable package and the android.view.animation package. These are collections of useful classes for maximizing bitmap imagery and for working with images that support the fourth dimension (time) via motion, commonly called animation.

Introducing the Drawables

The central set of classes used to control the graphics-related content within your Android application is called the drawable package. This package handles classes and methods related to drawing the following types of visual assets onto the Android display screen:

Bitmaps: In a bitmap, a collection of pixels make up an image—it’s a map of image bits, if you will. This is the most commonly used drawable asset.

Shapes: Shapes are line drawings. They also are known as vectors, like the lines architects use in CAD drawings. Common vector formats are EPS, AI, or SVG.

Gradients: Gradients are smooth transitions from one color to another color.They can be shaped in a straight line or occupy a circular area.

Transitions: Shape transitions are smooth vector changes between one shape and another shape. This process is sometimes referred to as morphing or tweening.

Animation: Animation involves an image, shape, or object that moves in some way.

Image transitions: These are smooth cross-fades between one image andanother image. They are usually used to smoothly transition from one image to another image.

In Android development, graphics-related items such as gradients, image transitions, animated transformations, and frame-based animation can all be termed drawables. With the exceptions of transformational (tween or procedural) animation, all of these center their resource assets in the /res/drawable folder.

The /res/drawable folder is also where you should put XML files that define things like frame-based image animations and cross fading image transitions.

Implementing Images :

Android is set up to automatically implement your images via the project folder Hierarchy. But once you get used to it, you’ll find that it is actually amazingly simple to use graphic resources, as extensive asset reference coding is all but eliminated.

Core Drawable Subclasses :

Android offers more than a dozen types of customized drawable objects. Look at the following core subclasses of android.graphics.drawable:

 BitmapDrawable object: Used to create, tile, stretch, and align bitmaps.

 ColorDrawable object: Used to fill certain other objects with color.

 GradientDrawable object: Used to create and draw custom gradients.

AnimationDrawable object: Used to create frame-based animations.

 TransitionDrawable object: Used to create crossfade transitions.

 LayerDrawable object: Used to create composited PNG32 bitmaps or WebP bitmaps via multiple image layers.

Bitmap Images :

Remember that a 32-bit PNG is a portable network graphic format with 8-bits of red, green, blue, and alpha (ARGB or RGBA) and that 4 × 8 = 32, thus: PNG32. Besides the WebP format that is supported in Android 4.0 and later, Android supports three mainstream bitmap image file formats: PNG, JPEG, and GIF.

PNG Images :

The most powerful file format that Android supports, and the one that it recommends using over all others, is the portable network graphics, or PNG (pronounced “ping”) format. There are two primary types of PNG:

Indexed-color PNG8, which uses a limited 256-color (8-bits of color allows 256 color values) image palette, which is an index of up to 256 colors that an image uses to make up its pixel colors

Truecolor PNG32, which uses a 32-bit color image that includes a full 8-bit alpha channel (used for image compositing) and 8-bits each of red, green, and blue image channels, or PNG24 for a truecolor PNG image with no alpha channel included.

PNG is known as a lossless image file format because it loses zero image data during the compression processing. This means that the image quality is always 100% maintained. If designers know what they are doing, they can get very high-quality graphics into a reasonably small data footprint by using either the indexed-color PNG8 or the truecolor PNG32 or PNG24 image file formats, depending upon how many colors are using in that image.

JPEG and GIF Images :

The next most desirable format to use is the JPEG image file type. This type does not have an alpha channel. It uses lossy compression, which means that it throws away some data to get a much better compression result, but at the expense of your image quality. JPEG stands for joint photographic experts group.

If you look closely at (zoom into, using GIMP) JPEG images, you will see a lot of artifacts, such as areas of strange color variations or what looks like dirt on the image (dirt that was not on the camera lens). JPEG is useful for much higher-resolution (print resolution) images, where artifacts are too small to be seen. So, it is not really as suitable for lower-resolution smartphone screens. 

JPEG is supported, but is not recommended for Android apps because Google wants their product to look as pristine as possible, and PNG or WebP formats are the sure-fire way to accomplish this.