Please help!!

Thank you all for your input and guidance! I actually figured it out just be converting/exporting it as PNG at 600 Dpi, worked like a charm.

Thanks again!

Alien Skin made a "Image Doctor" application that worked well in fixing JPegs artifacts and other compression problems like banding.  They also have an enlarging app called "Blowup".  You should try those or something similar.  It is tough to nail your specific problems without more info.

Zaydennoah,

Whichever unit the 24×36 poster is in (my guess is '), are you sure the resolution is inadequate (it may well be)?

If you can get no instructions concerning the required resolution at the final real size, you may:

1) Try to determine the real viewing distance, you may discuss it with the printer and/or client;

2) Choose a critical part of the banner with raster effects/image;

3) Determine its real width in the final print;

4) Calculate the ratio of the real viewing distance to the real width;

5) Create prints at whichever size you can on a (reasonably) good printer using resolutions/different raster effect settings scaled up to correspond to a range of (assumed relevant) full size real resolutions;

6) View each print at a viewing distance that has the same ratio to the printed width.

Your perception of smoothness versus jaggedness/pixelation at 6) will basically correspond to the perception at the full real size by the intended viewers at the corresponding full size real resolutions.

If the resolution is indeed inadequate, undoubtedly the best solution will be to get or remake the picture at an adequate resolution.

Failing that, you may fake it to a certain degree, best done in Photoshop (unfortunately the incredible Unblur Filter I saw demonstrated in a (Photoshop) Lounge thread some 15 years ago seems to have disappeared with the Lounge).

Unfortunately Image Trace won't improve the quality because even though you

get rid of pixelation, the process will add other artifacts/ look

that become apparent when you enlarge it.

Paying around with the settings isn't really going to help , unless you want a stylised arty look,

if you have access to  Photoshop, that has within limits, good enlargement technology:

Preserve Details 2.0 upscaling

Don't expect the image to get any better when you trace it.

What you are doing is not a "conversion".

You can edit Image colors or mode in Adobe Illustrator with Edit Colors under Edit Menu for reducing number of colors in your image. Also you can do that in Ps. May be these can enhance trace process.