"HP3325A - Fig 8.36 Control Circuits hi-res.jpg (876.81 kB, 2651x1174 )"
Oh god, please tell me you saved the original scans in a non-lossy format like PNG, and still have them?
Yes, those are huge files, but that's just the start. Because if you didn't go straight to JPG I can show you how to make them look really nice, in much smaller files. But if you only have JPGs, too late.
What did you use to scan the big foldout sheets? Or did you stitch them?
Stages:
- Scan as gray-scale, 256 levels, save as PNG. (Assuming there is no colour in the schematics. If there is, scan in full RGB colour.)
- (Stitching, in Photoshop for those with small scanners.)
- Remove blotches and any other defects. (A bunch of photoshop tricks, and maybe elbow grease, depending on how good the scans were.)
- White and black saturate, while retaining gray scale. The important thing is to remove *all* noise in the white background. This results in all those white areas later compressing to almost nothing in a run-length coding system like PNG. Second-most important is to not half-tone (FAX-ize) the edges - this is why gray scale must be preserved.
- Crop and scale to an optimal final size that retains the nice visual detail. Probably your 2651x1174 is a bit too large.
(All these stages must be done with non-lossy PNG intermediate files. NEVER ever use JPG for detailed images.)
- Finally, data-compress to final images by recoding in a more compact non-lossy format, such as PNG, 16 gray-levels (ie 4 bits per pixel.) Oh, and strip all the EXIF data, which is pointless.
You'll be amazed how small the files become.
- Optional bundling stage: Present in html for appearance, index, thumbnails etc, then wrap in some single-file format such as a RAR-book. Makes it convenient, while still having the raw images easily accessible as files, unlike PDF.
That's a simplified process description; assumes no photos, screened shading, colour overlays, etc.
Here's what JPG (a lossy wavelet-based coding system) does to images (part of your posted hi-res sample.)
All that gray dotty noise in the white areas is a result of the JPG scheme, and wasn't in the original scan data.
Once this kind of noise is injected into an image, it can never be removed.