On 04 Dec, wrote:

I looked at the earliest. This is a patchwork of bitmaps and overlaid
OCR'd text. I used pdfutils like pdfimages to examine the contents. The
patchwork images are jpegs.

In case anyone is interested, here is the start of the info for the April
1939 file on Keith's WW scans page. I've just listed the first 3 pages so
you can see the details of the contained patchwork of bitmaps. (This
utility ignores OCR'd text).

pdfimages -list Phase-Splitting_in_Push-Pull_Amplifiers.pdf
page num type width height color comp bpc enc interp object ID x-ppi
y-ppi size ratio
--------------------------------------------------------------------------------------------
1 0 image 589 828 gray 1 8 jpeg no 248 0 72
73 326B 0.1%
1 1 image 1140 1040 gray 1 8 jpeg no 249 0 300
300 63.8K 5.5%
1 2 image 736 12 gray 1 8 jpeg no 250 0 301
300 1965B 22%
1 3 image 728 992 gray 1 8 jpeg no 251 0 300
300 39.3K 5.6%
1 4 image 736 16 gray 1 8 jpeg no 252 0 301
301 2545B 22%
1 5 stencil 8 6 - 1 1 image no [inline] 600
600 - -
2 6 image 586 825 gray 1 8 jpeg no 235 0 73
72 383B 0.1%
2 7 image 996 988 gray 1 8 jpeg no 236 0 301
301 204K 21%
2 8 image 1144 796 gray 1 8 jpeg no 237 0 300
301 49.7K 5.6%
2 9 image 728 988 gray 1 8 jpeg no 238 0 300
301 35.5K 5.1%
2 10 image 1764 62 gray 1 8 jpeg no 239 0 601
600 10.1K 9.5%
2 11 image 86 49 gray 1 8 jpeg no 240 0 600
600 1643B 39%
3 12 image 586 825 gray 1 8 jpeg no 221 0 72
73 362B 0.1%
3 13 image 296 104 gray 1 8 jpeg no 222 0 300
306 8696B 28%
3 14 image 60 36 gray 1 8 jpeg no 223 0 299
304 1230B 57%
3 15 image 1132 768 gray 1 8 jpeg no 224 0 299
303 53.1K 6.3%
3 16 image 100 8 gray 1 8 jpeg no 225 0 300
327 377B 47%
3 17 image 1156 768 gray 1 8 jpeg no 226 0 299
304 57.0K 6.6%
3 18 image 752 20 gray 1 8 jpeg no 227 0 300
400 2356B 16%
3 19 image 1565 50 gray 1 8 jpeg no 228 0 600
757 7431B 9.5%

etc

Jim

--
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