adds fix_sigma_foveon_dngs script

Author: Stephan Kleinert

contrib/fix_sigma_foveon_dngs.lua

@@ -0,0 +1,110 @@
+--[[ fix-sigma-foveon-dngs-v0.1
+
+Fix Sigma Foveon DNGs white balance handling
+
+Copyright (C) 2025 Stephan Kleinert <[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
+
+This plugin provides a workaround for a bug that causes the colors in a
+Sigma Foveon DNG to be displayed incorrectly. The bug is described in
+depth here:
+
+https://github.com/darktable-org/darktable/issues/16586
+
+It works by disabling color calibration and resetting white balance
+to "as shot" upon first loading a Sigma Foveon DNG image in the darkroom. It
+is applied only once, i.e., you're free to adjust the white balance
+setting as you see fit without the plugin interfering on the next load.
+
+With many thanks to Bill Ferguson for pointing me on the right track.
+
+]]
+
+local dt = require "darktable"
+local du = require "lib/dtutils"
+local gettext = dt.gettext.gettext
+
+du.check_min_api_version("7.0.0", "fix_sigma_foveon_dngs")
+
+local function _(msgid)
+    return gettext(msgid)
+end
+
+-- return data structure for script_manager
+
+local script_data = {}
+
+script_data.metadata = {
+    name = _("Fix Sigma Foveon DNG files"),
+    purpose = _("Workaround for Sigma Foveon DNG white balance problems"),
+    author = "Stephan Kleinert <[email protected]>",
+    help = "https://schallundstille.de/"
+}
+
+script_data.destroy = nil -- function to destory the script
+script_data.destroy_method = nil -- set to hide for libs since we can't destroy them commpletely yet, otherwise leave as nil
+script_data.restart = nil -- how to restart the (lib) script after it's been hidden - i.e. make it visible again
+script_data.show = nil -- only required for libs since the destroy_method only hides them
+
+sad_cameras = { "sd Quattro", "sd Quattro H", "SIGMA dp2 Quattro",                  -- unfortunately, I've only ever had these
+                "SIGMA dp3 Quattro", "SIGMA dp1 Quattro", "SIGMA dp0 Quattro" }     -- not sure about these
+
+dt_fixed_tag = dt.tags.create("darktable|foveon_fixed")
+
+function contains(list, target)
+    for _, value in ipairs(list) do
+        if value == target then
+            return true
+        end
+    end
+    return false
+end
+
+local function fix_image()
+    -- first, disable colour calibration, as it wreaks havoc with sigma foveon DNGs
+    dt.gui.action("iop/channelmixerrgb/adaptation", "selection", "item:none (bypass)", 1,000, 0)
+    -- then, set white balance to "as shot", forcing the white balance module to re-read the white balance data from the DNG
+    -- (if there was a way to simply re-apply *this* setting via a preset, none of this would be necessary, just saying)
+    dt.gui.action("iop/temperature/settings/as shot", "", "on", 1,000)
+end
+
+local function fix_on_load(event, clean, image)
+    if not clean then
+        return
+    end
+    if image.exif_maker ~= "SIGMA" then
+        dt.print_log("[fix_sigma_foveon_dngs] ignoring non-Sigma image")
+        return
+    end
+    if not contains(sad_cameras, image.exif_model) then
+            dt.print_log("[fix_sigma_foveon_dngs] ignoring (seemingly) non-foveon camera: "..image.exif_model)
+        return
+    end
+    if contains(dt.tags.get_tags(image), dt_fixed_tag) then
+        dt.print_log("image already foveon_fixed")
+        return
+    end
+    fix_image()
+    dt.tags.attach(dt_fixed_tag, image)
+end
+
+dt.register_event("fix_sigma_foveon_dngs", "darkroom-image-loaded", fix_on_load)
+
+dt.print_log("[fix_sigma_foveon_dngs] loaded")