6.1.3 Dirty images

Your image may not be completely "clean", i.e., the scanning process may have introduced artifacts: black lines at the edge of the paper; blotches where the original had a speck of dirt or ink; broken lines where the image had a continuous line. To get a correct output font, you must correct these problems.

To remove blotches, you can simply put .notdef in the appropriate place in the IFI file. You can find the "appropriate place" when you look at the output font; some character will be nothing but a (possibly tiny) speck, and all the characters following will be in the wrong position.

The `-print-clean-info' option might also help you to diagnose which bounding boxes are being assigned to which characters, when you are in doubt. Here is an example of its output:

[Cleaning 149x383 bitmap: checking (0,99)-(10,152) ... clearing. checking (0,203)-(35,263) ... clearing. checking (0,99)-(130,382) ... keeping. checking (113,0)-(149,37) ... keeping. 106]

The final `106' is the character code output (ASCII `j'). The size of the overall bitmap which contains the `j' is 149 pixels wide and 383 pixels high. The bitmap contained four bounding boxes, the last two of which belonged to the `j' and were kept, and the first two from the adjacent character (`i') and were erased. (As shown in the example image above, the tail of the `j' often overlaps the `i' in type specimens.)

If the image has blobs you have not removed with .notdef, you will see a small bounding box in this output. The numbers shown are in "bitmap coordinates": (0,0) is the upper left-hand pixel of the bitmap.

If a blotch appears outside of the row of characters, Imageto will consider it to be its own (very small) image row. If you are using `-baselines', you must specify an arbitrary value corresponding to the blotch, even though the bounding box in the image will be ignored. See the section above for an example.