source:http://petrnohejl.github.io/Android-Cheatsheet-For-Graphic-Designers/#screen-densities-and-icon-dimensions

Android Cheatsheet for Graphic Designers

Graphic designers aren't programmers and sometimes don't know how to properly prepare graphic assets for developers. This simple cheatsheet should help them to do their job better, and to simplify developers' lives.

Content

Dimensions

Screen densities and icon dimensions

Qualifier	DPI	Scaling factor	Launcher icon	Action bar, tab icon	Notification icon (API 11)	Notification icon (API 9)	Notification icon (older)
ldpi	120	0.75	36 x 36 32 x 32	24 x 24 18 x 18	18 x 18 16 x 16	12 x 19 12 x 12	19 x 19 16 x 16
mdpi	160	1.0	48 x 48 42 x 42	32 x 32 24 x 24	24 x 24 22 x 22	16 x 25 16 x 16	25 x 25 21 x 21
hdpi	240	1.5	72 x 72 64 x 64	48 x 48 36 x 36	36 x 36 33 x 33	24 x 38 24 x 24	38 x 38 32 x 32
xhdpi	320	2.0	96 x 96 84 x 84	64 x 64 48 x 48	48 x 48 44 x 44	32 x 50 32 x 32	50 x 50 42 x 42
xxhdpi	480	3.0	144 x 144 126 x 126	96 x 96 72 x 72	72 x 72 66 x 66	48 x 75 48 x 48	75 x 75 63 x 63

Notice: the first icon dimension in table cell is full asset size, the second icon dimension is optical square. Dimension values are in pixels.

Tip: creating ldpi assets is not really needed anymore. The devices are rare and the platform will just scale down mdpi.

Sources and useful links: Iconography, Supporting Multiple Screens, Icon Design Guidelines,Dimension

Google Play asset dimensions

Asset Type	Required	Image type	Dimension
Screenshot	yes	JPEG or 24-bit PNG (no alpha)	min length for any side: 320 px max length for any side: 3840 px
High-res app icon	yes	32-bit PNG (with alpha)	512 x 512 px
Feature graphic	yes	JPEG or 24-bit PNG (no alpha)	1024 x 500 px
Promotional graphic	no	JPEG or 24-bit PNG (no alpha)	180 x 120 px
Video link	no	URL of YouTube video	-

Sources and useful links: Graphic and Image Assets, Google Play Featured-Image Guidelines,Iconography

Dimension units

Unit	Units / physical inch	Density independent	Same physical size on every screen
px	varies	no	no
in	1	yes	yes
mm	25.4	yes	yes
pt	72	yes	yes
dp	~160	yes	no
sp	~160	yes	no

Sources and useful links: Understanding Density Independence in Android

Size buckets

Type	Dimension
Handset	smaller than 600 dp
Tablet	larger than or equal 600 dp

Notice: one dp (density-independent pixel) is one pixel on a 160 DPI screen.

Sources and useful links: Metrics and Grids

Views dimensions and spacing

Touchable UI components are generally laid out along 48 dp units. Spacing between each UI element is 8 dp.

Sources and useful links: Metrics and Grids

Action bar height

Qualifier	Dimension
Portrait	48 dp
Landscape	40 dp
Tablet	56 dp

Sources and useful links: Action Bar

Type	Dimension
Micro	12 sp
Small	14 sp
Medium	18 sp
Large	22 sp

Images and themes

Nine-patch

A Nine-patch drawable is a stretchable bitmap image, which Android will automatically resize to accommodate the contents of the view in which you have placed it as the background, e.g. nine-patch background for button, which must stretch to accommodate strings of various lengths. The rules for nine-patch image are following:

Standard PNG image with alpha
Filename suffix is ".9.png", e.g. "btn_login_normal.9.png"
Image has an extra 1 pixel wide border, used to define the stretchable/static/padding areas
Stretchable sections are indicated by 1 px wide black line(s) in the left and top part of the border
Static sections are indicated by fully transparent or white pixels
Padding area (optional) is indicated by 1 px wide black line in the right and bottom part of the border

Sources and useful links: Canvas and Drawables, Draw 9-patch, Simple Nine-patch Generator

Colors

Use color primarily for emphasis. Blue is the standard accent color in Android's color palette. Note that red and green may be indistinguishable to color-blind users. Primary colors are as follows:

#33B5E5
#AA66CC
#99CC00
#FFBB33
#FF4444

#0099CC
#9933CC
#669900
#FF8800
#CC0000

Sources and useful links: Color

Holo themes

Android provides three system themes:

Holo Light
Holo Dark
Holo Light with dark action bar

Sources and useful links: Themes, Holo Everywhere

Naming conventions

Naming conventions for drawables

File names must contain only lowercase a-z, 0-9, or _.

Drawables for the specific views (ListView, TextView, EditText, ProgressBar, CheckBox etc.) should be named like this views keeping the naming rules, e.g. drawable for CheckBox should be named "checkbox_on_bg.png".

Asset Type	Prefix	Example
Action bar	`ab_`	`ab_stacked.9.png`
Button	`btn_`	`btn_send_pressed.9.png`
Dialog	`dialog_`	`dialog_top.9.png`
Divider	`divider_`	`divider_horizontal.9.png`
Icon	`ic_`	`ic_star.png`
Menu	`menu_`	`menu_submenu_bg.9.png`
Notification	`notification_`	`notification_bg.9.png`
Tabs	`tab_`	`tab_pressed.9.png`

Sources and useful links: naming conventions taken from the Android SDK

Naming conventions for icon assets

Asset Type	Prefix	Example
Icons	`ic_`	`ic_star.png`
Launcher icons	`ic_launcher`	`ic_launcher_calendar.png`
Action bar icons	`ic_menu`	`ic_menu_archive.png`
Status bar icons	`ic_stat_notify`	`ic_stat_notify_msg.png`
Tab icons	`ic_tab`	`ic_tab_recent.png`
Dialog icons	`ic_dialog`	`ic_dialog_info.png`

Sources and useful links: Icon Design Guidelines

Naming conventions for selector states

State	Suffix	Example
Normal	`_normal`	`btn_order_normal.9.png`
Pressed	`_pressed`	`btn_order_pressed.9.png`
Focused	`_focused`	`btn_order_focused.9.png`
Disabled	`_disabled`	`btn_order_disabled.9.png`
Selected	`_selected`	`btn_order_selected.9.png`

Sources and useful links: Touch Feedback

Organizing drawables to directories

One drawable must have the same file name for all screen densities (ldpi, mdpi, hdpi etc.) and all these files must be organized according to density into the following directories. Here's the resources directory structure for drawables:

res
- drawable-ldpi
- drawable-mdpi
- drawable-hdpi
- drawable-xhdpi
- drawable-xxhdpi

Android Tutorial

Tuesday, 18 August 2015