[Galaxy S II Themes and Apps] Tungstwenty:
As reported in multiple places on the forum, stock ICS ROMs do not come with the CRT-Off effect available, although the code is there and lots of existing mods already exist to be able to turn it on.

The implementation, however, contains a glitch and every once in a while the full screen image will blink right after the beam collapses.

I have managed to apply the fix to the Sammy's custom library that implements this, even though the source code is not available. (this wouldn't be possible without the good folks on CM9, though!).

The discussion that lead to this work can be found here, on the awesome JKay mod. BTW, if this fix is useful to you, do me a favor a buy that man's Deluxe app (it's really a favor you're doing to yourself, not me :)).

For any ROM cookers, MOD developers, or end-users, I leave the patched file and a few instructions to make sure the provided lib only changes the flicker part. This is because I have performed the changes on the file shipped on XWLP9, and if other different files exist in other builds, it's more convenient to apply the fix there instead of using the lib from a different ROM and possibly lose some other improvements or fixes applied by Samsung.

Please check the Readme file in the archive for instructions on what to confirm and how to apply the change, and let me know if there's any question or if you have a different base version.

EDIT:

The library has been updated to handle CRT-On effect as well. You can safely replace it with the attached version, although you'll need to have a mod to activate the CRT-On effect as well.

If you want to install a standalone patch to activate this, have a look at this post and follow the instructions.

Technical notes

The code has been revised to display 8 frames when turning on - as opposed to 24 when turning off - in order to have a faster response. This is however still dependent on the time taken by the kernel to wake the CPU, before drawing can begin (currently about 1s). This delay will not happen if you don't wait long enough after turning off, as the CPU will not enter deep sleep.

Changes from Kamma have also been applied, in order to have a similar effect when turning On - "normal" screen colors instead of random color spikes. This might be barely noticeable due to the animation speed.

EDIT2:

No more issues with the library, it now works perfectly with Youtube playing videos, etc. Also the CRT-On effect is now very smooth (although faster than CRT-Off, on purpose).

Major kudos to rovo89 for turning an initial hack to fix the glitches in a polished final product!!! :)

Be aware that this just contains the library for the effects to work properly. You'll still need your ROM to be modded to activate them (instructions included in this zip file), or, better yet, install rovo89's Xposed Tweakbox module which overrides the behavior without replacing any files and should work even with non-stock roms.

Out of the box solutions for getting the CRT effects

Tweakbox by rovo89 (and a bit of help from myself) - works for pretty much all stock roms and derivatives, odexed or deodexed. It's even working for S3, since it contains a patched file from that model.

If you're using Deodexed XWLPG, you can also go to this post by The Undertakerr and fetch a flashable zip that contains everything that's needed to have CRT_On and CRT_Off effects always active.