TIAdigitizer
This board is inserted between the TIA chip and its socket in the Atari 2600 game console. The FPGA on the board listens to the digital communication between the TIA and the rest of the system and re-generates the video output in a near-digital form. This output signal (we call it 'lumacode') can then be flawlessly upscaled to a pixel-perfect HDMI signal using an RGBtoHDMI device or something with equal capabilities.
With the extremely low quality of the original video signal from the Atari 2600 consoles, this is a very impactful and fairly easy upgrade. It will also extend the product family of lumacode boards.
While there are other existing video upgrades for this machine, the TIAdigitizer is fairly easy to install and can give you a 100% pixel perfect digital image via a compatible upscaler (whis is only the RGBtoHDMI at present).
The board is designed to work will all variants (PAL or NTSC) of the Atari 2600. Maybe there is a space issue with the smaller Jr. version, but I can not tell as long as nobody has tried this yet. The mod board adds about 4mm of height to the TIA chip. And if your TIA is not socketed to begin with, you may want to add one more socket.
One more thing to mention: Because the vertical refresh rate is under software control of the respective game, the output HDMI refresh rate may also vary and could cause your monitor to lose synchronization when the game changes its behaviour.
More details are available on the project documentation page.