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authorNorbert Preining <norbert@preining.info>2019-09-02 13:46:59 +0900
committerNorbert Preining <norbert@preining.info>2019-09-02 13:46:59 +0900
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+This file is README.WRITE-W. It is extracted from a correspondence
+message sent during September, 1986.
+
+From: Neenie Billawala <nb@su-coyote.arpa>
+Subject: Re: Metafont parameters for Imagen 24/300
+ (This discussion is also relevant for the LN03)
+
+How to get the CM fonts to work better on a "write-white" machine
+=================================================================
+
+
+The problem in getting a like result with write-white(ww)/write-black(wb)
+machines from the same pixel pattern lies in the fact that the effective
+size of each pixel differs; the size is typically smaller in ww machines.
+This means that you won't get the same variations in line thickness.
+
+Theoretically, one pixel on a 300dpi printer should have a width of 1/300
+of an inch. On a ww machine, it's typically less; on a wb machine,
+it's usually a bit more. So the gradations of thickness may look
+something like the following:
+
+# of pixels "ideal width" ww width wb width
+
+ 1 1 * 1/300inch .8 * 1/300inch 1.2*1/300inch
+ 2 2 * 1/300inch 1.8 * 1/300inch 2.2*1/300inch
+ 3 3 * 1/300inch 2.8 * 1/300inch 3.2*1/300inch
+ 4 4 * 1/300inch 3.8 * 1/300inch 4.2*1/300inch
+ 10 10 * 1/300inch 9.8 * 1/300inch 10.2*1/300inch
+
+So, you can see, the greater the number of pixels, the less important
+the .4 pixel difference becomes. The greatest discrepancy and problems
+occur with lines one pixel wide, where the % of difference is the greatest.
+Given these limitations, it is not possible to get exactly the same
+results on two such separate machines.
+
+Increasing the amount of "blacker" has the effect of adding that
+absolute amount to certain values; i.e., blacker:=2 would always add
+2 pixels to the stem, no matter the resolution.
+
+A while back, someone came by with the same problem for a similar machine.
+We tried 1) some higher settings of blacker 2) selectively adding blacker
+to some values 3) setting a mimimum line thickness. Both 1) and 2) often
+created unwanted character distortions. The (tfm) widths wanted to be
+the same, and when e.g., each line in a character was increased by one;
+the shapes were often distorted, counter (inside) shapes seemed to suffer
+the most. A first attempt with 3) showed promise, and though the result
+was not as dark as the wb machine, the feeling of CM was retained.
+However, in the first attempt, we did not manage to change all of the
+thicknesses to 2 pixels. DEK made a global correction, which should keep
+minimum thicknesses to 2 pixels. Looking at the pixel patterns, this fix
+appears to work. However, the man who has the ww printer and who originally
+came by with this problem, is part of the University and has been traveling,
+so I haven't seen any concrete results yet. Such is the way of Academia!
+
+
+Appendix: (Pierre A. MacKay)
+
+
+Roughly speaking, the reason for this problem is that the black dot in
+a write-black machine has a roughly round shape, and naturally tends to
+overflow the minimum dot size. The dot on a write-white machine has an
+incluse square shape, and tends to be diminished by an oversize white
+dot unless the print engine is perfectly focussed.
+
+ .....
+ ....... . .
+ ......... .....
+ ......... .....
+ ......... .....
+ ....... . .
+ .....
+
+ Write-black dot Write-white dot
+
+The ./cmfonts/mf directory contains an adjusted font_setup file. The
+changes are found in 2 lines of the <font_setup> def with the comment
+"% "WRITE WHITE" ONLY!". Add the line input white_setup to your file
+of mode_defs (or use ./utilityfonts/bases/modes.mf, which already
+has it), and in any mode_def for a write-white device, add the line
+
+let font_setup=white_setup;
+
+as the first line of the mode_def for any write-white device
+(see the RicohFourZeroEightZero mode_def in modes.mf).
+
+Directories
+[
+ ./utilityfonts/bases
+ ./cmfonts/mf
+]