I want to take raw image of my android system partition either on sdcard or on my pc using adb or any other way.. if their is way please help
Here's how to get a system dump from Android:
Prepare Your PC
Ensure that your computer has the most recent version of the Java Development Kit installed. If it doesn't, download and install the most recent JDK from Oracle's Java SE Downloads page.
Navigate to the Download the Android SDK page on the Android Developers website in a Web browser and download the installer package to your computer. Double-click the downloaded file and follow the installation prompts.
Navigate in Windows Explorer to the location where you installed the SDK. By default, this is C:\Program Files\Android\android-sdk.
Double-click the SDK Manager to launch it. In the left pane file tree, check the box next to "Android SDK Platform-tools." Click "Install Packages." A confirmation window appears. Click the radio button next to "Accept All." Click "Install." A progress bar appears.
Prepare Your Phone
Press your phone's menu button from the Home screen. Tap "Settings." The Settings menu appears.
Tap "Applications." In the Application Settings menu, tap "Development."
Check the box next to "USB Debugging" in the Development menu.
Get a System Dump
Press "R" and the Windows key simultaneously on your PC keyboard to bring up the Run box. Type "cmd."
Type the following into the command window:
cd C:\Program Files\Android\android-sdk\platform-tools
Type "adb.exe shell."
su dd if=/dev/block/stl6 of=/sdcard/factoryfs.rfs at the ABD shell prompt. Replace "/sdcard/factoryfs.rfs" with the location to copy the file to if you don't want it on the phone's SD Card.
Reproduced in full from this site