Fastest method for screen capturing on Linux

Question

This question is similar to this one

Fastest method of screen capturing

but for linux/X11.

To be more specific, i need a method to capture the pixel

Answer 1

Xpaint is a very old X11 utility built using the MIT Athena widget set. File > Take Snapshot will grab a window or mouse-selected rectangle from screen.

OR

MagiCapture is a screen capture and preview utility for the X Window System. A user may capture a single window, a single window with decorations, a rectangular region of the display, or the entire display itself. The user may save the captured image into a graphics file supported by the ImageMagick toolkit, which supports most (if not all) popular graphics formats. MagiCapture uses the GLIB and GTK+ libraries for the user interface and the ImageMagick and GdkMagick library for all graphics processing. Requires ImageMagick.

OR

Zscreen:- This Windows-only screen capture app has tons of features. It grabs a shot of the active window, a selected window, or the entire screen. Once you've got the image, automatically open it in your image editor or upload it to Twitpic, YFrog, Flickr, or one of several other supported services. ZScreen caches all your images, even ones on the clipboard, so there's always a history of your screenshots right at your fingertips.