They were all halftones. While descreening was applied, structure due to the halftone screen can still be seen in the images. Both because of the halftones and the textures in the images, those images seen on the pages have been considerable processed in order to keep the size of the resultant file reasonable. This was more successful in reducing the file size in some cases more than in others due to different image structure. It is impossible, at the resolutions and file sizes that are available, to give a reasonable rendition of the original work.
Larger images are available as well, linked to the images on the pages.
Even so, I urge you to visit the original murals. The biographies were prepared in 1981. The only update included is the date of the tragic death of Helen Hardin. I will attempt to acquire updated biographies of the artists.