Signal Processing: Image Compression:

I want to store full-color text images in JPEG or TIFF-JPEG format. These images contain text documents with some color graphics. Even with very high JPEG Quality levels, there is still a lot of artifacts and degradations on the text.

I have total control of the JPEG encoding parameters, including subsampling ratios and quantization matrix.

My question is:

• Can I optimize those parameters for text documents? (Beyond the quality level)
• Can I apply different parameter settings for different parts of the image?
• Would it help if I manually truncate (quantize) the coefficients for different parts of the images, before encoding?

(Will attach sample image later coz can't access imgur at office.)