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	tAdd reciprocity failure program - filmtools - various tools for photographic f…
	git clone git://src.adamsgaard.dk/filmtools
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	commit 3546ae81af5a877bae48e2e2592c504cebc0dc1a
	parent 3e5d5e3b1968d4e4fabc24578adfa551d4331766
	Author: Anders Damsgaard <[email protected]>
	Date: Thu, 16 Jul 2020 22:09:51 +0200

	Add reciprocity failure program

	Diffstat:
	A reciprocity.1 \| 50 +++++++++++++++++++++++++++++…
	A reciprocity.c \| 85 +++++++++++++++++++++++++++++…

	2 files changed, 135 insertions(+), 0 deletions(-)
	---
	diff --git a/reciprocity.1 b/reciprocity.1
	t@@ -0,0 +1,50 @@
	+.Dd JULY 16, 2020
	+.Dt RECIPROCITY 1
	+.Os
	+.Sh NAME
	+.Nm reciprocity
	+.Nd calculates compensated exposure time for film reciprocity failure
	+.Sh SYNOPSIS
	+.Nm
	+.Ar film
	+.Ar time
	+.Sh DESCRIPTION
	+Photographic films suffer from low-intensity reciprocity failure
	+during long exposures (usually >1 s). This program returns the
	+compensated exposure time.
	+.Bl -tag -width Ds
	+.It Ar film
	+specifies the film type and can be one of the following:
	+.Bl -bullet -compact
	+.It
	+panf
	+.It
	+fp4
	+.It
	+hp5
	+.It
	+delta100
	+.It
	+delta400
	+.It
	+delta3200
	+.It
	+sfx
	+.It
	+xp2
	+.It
	+acros100
	+.It
	+tmx
	+.It
	+tmy
	+.It
	+tmz
	+.It
	+trix
	+.El
	+.It Ar time
	+is metered exposure time in format MM:SS
	+.El
	+.Sh AUTHORS
	+.An Anders Damsgaard Aq Mt [email protected]
	diff --git a/reciprocity.c b/reciprocity.c
	t@@ -0,0 +1,85 @@
	+#include <stdio.h>
	+#include <unistd.h>
	+#include <err.h>
	+#include <math.h>
	+#include <string.h>
	+
	+#define LENGTH(X) (sizeof X / sizeof X[0])
	+
	+typedef struct {
	+ const char *manufacturer;
	+ const char *name;
	+ double factor;
	+ double exponent;
	+} Film;
	+
	+static const Film films[] = {
	+ { "ilford", "panf", 1.00, 1.33 },
	+ { "ilford", "fp4", 1.00, 1.26 },
	+ { "ilford", "hp5", 1.00, 1.31 },
	+ { "ilford", "delta100", 1.00, 1.26 },
	+ { "ilford", "delta400", 1.00, 1.41 },
	+ { "ilford", "delta3200", 1.00, 1.33 },
	+ { "ilford", "sfx", 1.00, 1.43 },
	+ { "ilford", "xp2", 1.00, 1.31 },
	+ { "fujifilm", "acros100", 0.96, 1.02 },
	+ { "kodak", "tmx", 1.18, 1.13 },
	+ { "kodak", "tmy", 1.05, 1.22 },
	+ { "kodak", "tmz", 1.34, 1.20 },
	+ { "kodak", "trix", 2.41, 1.29 },
	+};
	+
	+char *argv0;
	+
	+static void
	+usage()
	+{
	+ int i;
	+
	+ printf("usage: %s film time\n", argv0);
	+ puts("where time is metered exposure time in format MM:SS,");
	+ puts("and film is one of the following:");
	+ for (i = 0; i < LENGTH(films); i++)
	+ printf(" %-12s (%s)\n", films[i].name, films[i].manufacture…
	+}
	+
	+int
	+main(int argc, char **argv)
	+{
	+ double exponent;
	+ int i, min, sec, sec_equiv;
	+
	+ argv0 = *argv;
	+
	+#ifdef __OpenBSD__
	+ if (pledge("stdio", NULL) == -1)
	+ errx(1, "pledge");
	+#endif
	+
	+ if (argc != 3) {
	+ usage();
	+ errx(1, "incorrect arguments");
	+ }
	+
	+ for (i = 0;; i++) {
	+ if (i == LENGTH(films))
	+ errx(3, "unknown film type");
	+ if (strncasecmp(argv[1], films[i].name, 10) == 0) {
	+ exponent = films[i].exponent;
	+ break;
	+ }
	+ }
	+
	+ printf("exponent: %g\n", exponent);
	+
	+ if (sscanf(argv[2], "%d:%d", &min, &sec) != 2)
	+ errx(2, "could not parse time in MM:SS format");
	+
	+ sec_equiv = pow(min*60 + sec, exponent);
	+
	+ printf("%d:%02d\n",
	+ (int)(sec_equiv/60.0),
	+ (int)(sec_equiv)%60);
	+
	+ return 0;
	+}