OpenPHDGuiding · bwdev01 · Jan 7, 2025 · Nov 6, 2024 · Nov 9, 2024 · Nov 9, 2024
diff --git a/help/Darks_BadPixel_Maps.htm b/help/Darks_BadPixel_Maps.htm
@@ -2,16 +2,45 @@
 <html><head><meta content="text/html; charset=ISO-8859-1" http-equiv="content-type"><title>Darks_BadPixel_Maps</title></head>
 <body><h2>Dark Frames and Bad-pixel Maps</h2><br><h3>Introduction</h3>Cameras
 used for guiding are typically not temperature-regulated and may
-produce&nbsp;images that appear quite&nbsp;noisy. &nbsp;As a result, guide
+produce&nbsp;images that appear quite&nbsp;noisy. This is particularly
+true of older CCD-based guide cameras.&nbsp; As a result, guide
 exposures frequently show obvious&nbsp;defects in the form of &nbsp;hot
-(or "warm") pixels or regions with spurious brightness levels. &nbsp;If
+(or "warm") pixels or regions with spurious brightness levels.
+&nbsp;For convenience, we refer to these areas of sensor noise as "hot
+pixels" but they may be larger than 1 pixel in size and have arbitrary
+brightness levels.&nbsp; If
 there are too many of these defects, PHD2 may have trouble identifying
-and selecting&nbsp;guide stars. &nbsp;Even after guiding has begun, a
-spurious hot pixel close to the guide star can disrupt the calculations
-needed for smooth guiding and may cause the software to "jump" between
+and selecting&nbsp;guide stars. &nbsp;This is especially true when sky
+conditions are poor and there are few or even zero actual guide stars
+available. The "MinHFD" and "MaxHFD" settings provide the best defense
+against mistaking&nbsp;sensor noise for stars, but a dark library or
+bad-pixel map provides an extra level of protection.&nbsp; Even after
+guiding has begun, a
+spurious hot pixel close to the guide star can disrupt the calculation
+of the guide star position and may cause the guiding&nbsp; to "jump"
+between
 the real star and the hot pixel. &nbsp;These sorts of problems can be
-mitigated by using either of two approaches in PHD2: dark frames and
-bad pixel maps. &nbsp;All functions related to dark frames and bad-pixel maps are located under the top-level 'Darks' menu.<br><br>&nbsp;&nbsp;<h3><a name="Dark_Frames"></a>Dark Frames</h3>PHD2 will
+mitigated by using either of two approaches in PHD2: dark frames or
+bad pixel maps. &nbsp;All functions related to dark frames and
+bad-pixel maps are located under the top-level 'Darks' menu.<br><br>Since
+the dark libraries and bad pixel maps rely on raw ADU values returned
+by the camera driver, they are&nbsp;implicitly dependent on camera
+settings that affect these ADU levels. &nbsp;These include the camera
+bit-depth and the camera gain. &nbsp;Bit-depth is the term used to
+indicate whether the driver returns image data in 8-bit or 16-bit
+format. &nbsp;Even though some camera electronics may use 10, 12, or
+14-bit values internally, the image data will be scaled and delivered
+to PHD2 as 16-bit data. Many cameras operate in only one bit-depth
+mode, in which case you don't need to think about it. &nbsp;But some
+guide cameras support either mode and you will need to&nbsp;choose or
+at least be aware of which mode is active before building a dark
+library or a bad-pixel map. &nbsp;If you subsequently change bit-depth
+settings, you will need to repeat the process of building them.
+&nbsp;The camera gain setting is a bit different in that it&nbsp;scales
+the ADU levels in an arbitrary way. &nbsp;Small changes in gain are
+unlikely to have much effect on the dark library/bad-pix map data but
+large changes will invalidate them. &nbsp;For this reason, we
+discourage people from making frequent adjustments to the camera gain.<br><br>&nbsp;&nbsp;<h3><a name="Dark_Frames"></a>Dark Frames</h3>PHD2 will
 build and use a&nbsp;library of dark frames that match the range of
 exposures you use for guiding. &nbsp;Once the library is built, it will
 be saved automatically and will be available for use across multiple

diff --git a/src/darks_dialog.cpp b/src/darks_dialog.cpp
@@ -207,6 +207,14 @@ DarksDialog::DarksDialog(wxWindow *parent, bool darkLib)
     pvSizer->Add(phSizer, wxSizerFlags().Border(wxALL, 5));
     pvSizer->Add(m_pProgress, wxSizerFlags().Border(wxLEFT, 60));
 
+    wxStaticText *bppWarning =
+        new wxStaticText(this, wxID_ANY, _("Be sure camera bit-depth is already set to desired value (8-bit or 16-bit)"),
+                         wxPoint(-1, -1), wxSize(-1, -1));
+    wxFont font = bppWarning->GetFont();
+    font.SetWeight(wxFONTWEIGHT_BOLD);
+    bppWarning->SetFont(font);
+    pvSizer->Add(bppWarning, wxSizerFlags().Center().Border(wxALL, 4));
+
     // Buttons
     wxBoxSizer *pButtonSizer = new wxBoxSizer(wxHORIZONTAL);
     m_pResetBtn = new wxButton(this, wxID_ANY, _("Reset"));

diff --git a/src/scope.cpp b/src/scope.cpp
@@ -2088,7 +2088,8 @@ ScopeConfigDialogCtrlSet::ScopeConfigDialogCtrlSet(wxWindow *pParent, Scope *pSc
                                                      wxDefaultPosition, wxSize(width, -1), wxSP_ARROW_KEYS, MAX_DURATION_MIN,
                                                      MAX_DURATION_MAX, 150, _T("MaxDec_Dur"));
             AddLabeledCtrl(CtrlMap, AD_szMaxDecAmt, _("Max Dec duration"), m_pMaxDecDuration,
-                           _("Longest length of pulse to send in declination\nDefault = 2500 ms.  Increase if drift is fast."));
+                           _("Longest length of pulse to send in declination\nDefault = 2500 ms. NOTE: this will be ignored if "
+                             "backlash compensation is enabled"));
 
             wxString dec_choices[] = {
                 Scope::DecGuideModeLocaleStr(DEC_NONE),