Merge pull request darktable-org#314 from dtorop/fujifilm-dynamic-range

Fujifilm dynamic range

Author: wpferguson

contrib/fujifilm_dynamic_range.lua

@@ -0,0 +1,109 @@
+--[[ fujifilm_dynamic_range-0.1
+
+Compensate for Fujifilm raw files made using "dynamic range".
+
+Copyright (C) 2021 Dan Torop <[email protected]>
+
+This program is free software; you can redistribute it and/or modify
+it under the terms of the GNU General Public License as published by
+the Free Software Foundation; either version 2 of the License, or
+(at your option) any later version.
+
+This program is distributed in the hope that it will be useful,
+but WITHOUT ANY WARRANTY; without even the implied warranty of
+MERCHANTABILITY or FITNESS FOR A PARTICULAR PURPOSE.  See the
+GNU General Public License for more details.
+
+You should have received a copy of the GNU General Public License along
+with this program; if not, write to the Free Software Foundation, Inc.,
+51 Franklin Street, Fifth Floor, Boston, MA 02110-1301 USA.
+]]
+
+--[[About this Plugin
+Support for adjusting darktable exposure by Fujifilm raw exposure
+bias. This corrects for a DR100/DR200/DR400 "dynamic range" setting.
+
+Dependencies:
+- exiftool (https://www.sno.phy.queensu.ca/~phil/exiftool/)
+
+Based upon fujifilm_ratings by Ben Mendis
+
+The relevant tag is RawExposureBias (0x9650). This appears to
+represent the shift in EV for the chosen DR setting (whether manual or
+automatic). Note that even at 100DR ("standard") there is an EV shift:
+
+100 DR -> -0.72 EV
+200 DR -> -1.72 EV
+400 DR -> -2.72 EV
+
+The ideal would be to use exiv2 to read this tag, as this is the same
+code which darktable import uses. Unfortunately, exiv2 as of v0.27.3
+can't read this tag. As it is encoded as a 4-byte ratio of two signed
+shorts -- a novel data type -- it will require some attention to fix
+this.
+
+There is an exiv2-readable DevelopmentDynamicRange tag which maps to
+RawExposureBias as above.  DevelopmentDynamicRange is only present
+when tag DynamicRangeSetting (0x1402) is Manual/Raw (0x0001). When it
+is Auto (0x0000), the equivalent data is tag AutoDynamicRange
+(0x140b). But exiv2 currently can't read that tag either.
+
+Hence for now this code uses exiftool to read RawExposureBias, as a
+more general solution. As exiftool is approx. 10x slower than exiv2
+(Perl vs. C++), this may slow large imports.
+
+These tags have been checked on a Fujifilm X100S and X100V. Other
+cameras may behave in other ways.
+
+--]]
+
+local dt = require "darktable"
+local du = require "lib/dtutils"
+local df = require "lib/dtutils.file"
+
+du.check_min_api_version("4.0.0", "fujifilm_dynamic_range")
+
+local function detect_dynamic_range(event, image)
+	if image.exif_maker ~= "FUJIFILM" then
+		dt.print_log("[fujifilm_dynamic_range] ignoring non-Fujifilm image")
+		return
+	end
+	-- it would be nice to check image.is_raw but this appears to not yet be set
+	if not string.match(image.filename, "%.RAF$") then
+		dt.print_log("[fujifilm_dynamic_range] ignoring non-raw image")
+		return
+	end
+	local command = df.check_if_bin_exists("exiftool")
+	if not command then
+		dt.print_error("[fujifilm_dynamic_range] exiftool not found")
+		return
+	end
+	local RAF_filename = df.sanitize_filename(tostring(image))
+	-- without -n flag, exiftool will round to the nearest tenth
+	command = command .. " -RawExposureBias -n -t " .. RAF_filename
+	dt.print_log(command)
+	output = io.popen(command)
+	local raf_result = output:read("*all")
+	output:close()
+	if #raf_result == 0 then
+		dt.print_error("[fujifilm_dynamic_range] no output returned by exiftool")
+		return
+	end
+	raf_result = string.match(raf_result, "\t(.*)")
+	if not raf_result then
+		dt.print_error("[fujifilm_dynamic_range] could not parse exiftool output")
+		return
+	end
+	if image.exif_exposure_bias ~= image.exif_exposure_bias then
+		-- is NAN (this is unlikely as RAFs should have ExposureBiasValue set)
+		image.exif_exposure_bias = 0
+	end
+	-- this should be auto-applied if plugins/darkroom/workflow is scene-referred
+	-- note that scene-referred workflow exposure preset also pushes exposure up by 0.5 EV
+	image.exif_exposure_bias = image.exif_exposure_bias + tonumber(raf_result)
+	dt.print_log("[fujifilm_dynamic_range] raw exposure bias " .. tostring(raf_result))
+end
+
+dt.register_event("post-import-image", detect_dynamic_range)
+
+dt.print_log("[fujifilm_dynamic_range] loaded")