diff --git a/backend/genesys.c b/backend/genesys.c
index 64ec498e3..c815dabdc 100644
--- a/backend/genesys.c
+++ b/backend/genesys.c
@@ -3053,7 +3053,7 @@ genesys_send_shading_coefficient (Genesys_Device * dev)
       break;
     case CCD_KVSS080:
     case CCD_G4050:
-      target_code = 0xe000;
+      target_code = 0xf000;
       free(shading_data);
       length=compute_gl843_coefficients (dev,
 			                 &shading_data,
diff --git a/backend/genesys_devices.c b/backend/genesys_devices.c
index 9f44ed953..ebc52771b 100644
--- a/backend/genesys_devices.c
+++ b/backend/genesys_devices.c
@@ -506,12 +506,12 @@ static Genesys_Sensor Sensor[] = {
   ,
   {CCD_G4050,
    4800,
-   38*8,	/* 38 at 600 dpi */
-   31*8,	/* 31 at 600 dpi */
+   50*8,	/* black_pixels */
+   31,	        /* 31 at 600 dpi dummy_pixels */
    152,
    5360*8,      /* 5360 max at 600 dpi */
-   210,
-   230,
+   190,
+   190,
    /* 08    09    0a    0b */
    {0x00, 0x00, 0x18, 0x69} ,
    /* 10    11    12    13    14    15    16    17    18    19    1a    1b    1c    1d */
@@ -1215,7 +1215,7 @@ static Genesys_Model hpg4050_model = {
   {16, 8, 0},			/* possible depths in color mode */
 
   SANE_FIX (6.55),		/* Start of scan area in mm  (x) */
-  SANE_FIX (15.00),		/* Start of scan area in mm (y) */
+  SANE_FIX (13.00),		/* Start of scan area in mm (y) */
   SANE_FIX (217.9),		/* Size of scan area in mm (x) 5148 pixels at 600 dpi*/
   SANE_FIX (315.0),		/* Size of scan area in mm (y) */
 
@@ -1234,7 +1234,9 @@ static Genesys_Model hpg4050_model = {
   SANE_FIX (0.0),		/* Amount of feeding needed to eject document 
 				   after finishing scanning in mm */
 
-  0, 37, 74,		/* RGB CCD Line-distance correction in line number */
+  0, 24, 48,		        /* RGB CCD Line-distance correction in line number */
+  				/* 0 38 76 OK 1200/2400 */
+  				/* 0 24 48 OK [100,600] dpi */
 
   COLOR_ORDER_RGB,		/* Order of the CCD/CIS colors */
 
@@ -1246,8 +1248,9 @@ static Genesys_Model hpg4050_model = {
   MOTOR_G4050,
   GENESYS_FLAG_LAZY_INIT | 	/* Which flags are needed for this scanner? */
   GENESYS_FLAG_OFFSET_CALIBRATION |
-  GENESYS_FLAG_DARK_CALIBRATION |
   GENESYS_FLAG_STAGGERED_LINE |
+  GENESYS_FLAG_SKIP_WARMUP |
+  GENESYS_FLAG_DARK_CALIBRATION |
   GENESYS_FLAG_CUSTOM_GAMMA,
   GENESYS_HAS_SCAN_SW | GENESYS_HAS_FILE_SW | GENESYS_HAS_COPY_SW,
   100,
diff --git a/backend/genesys_gl843.c b/backend/genesys_gl843.c
index 46dc7d3e1..85d75efff 100644
--- a/backend/genesys_gl843.c
+++ b/backend/genesys_gl843.c
@@ -1135,7 +1135,7 @@ gl843_init_optical_regs_scan (Genesys_Device * dev,
   dpiset = used_res * cksel;
 
   /* start and end coordinate in optical dpi coordinates */
-  startx = (start + dev->sensor.dummy_pixel)/cksel;
+  startx = (start + dev->sensor.dummy_pixel * tgtime)/cksel;
 
   used_pixels=pixels/cksel;
   endx = startx + used_pixels;
@@ -1288,7 +1288,7 @@ gl843_init_optical_regs_scan (Genesys_Device * dev,
   DBG (DBG_io2, "%s: exposure used=%d\n", __FUNCTION__, exposure/tgtime);
 
   r = sanei_genesys_get_address (reg, REG_DUMMY);
-  r->value = dev->sensor.dummy_pixel/factor;
+  r->value = dev->sensor.dummy_pixel * tgtime;
 
   DBGCOMPLETED;
   return SANE_STATUS_GOOD;
@@ -3116,7 +3116,7 @@ gl843_offset_calibration (Genesys_Device * dev)
 
   /* offset calibration is always done in color mode */
   channels = 3;
-  lines=1;
+  lines=8;
   bpp=8;
 
   /* compute divider factor to compute final pixels number */
@@ -3283,7 +3283,7 @@ gl843_coarse_gain_calibration (Genesys_Device * dev, int dpi)
   int bpp;
 
   DBG (DBG_proc, "gl843_coarse_gain_calibration: dpi = %d\n", dpi);
-  dpihw=sanei_genesys_compute_dpihw(dev,dev->settings.xres);
+  dpihw=sanei_genesys_compute_dpihw(dev, dpi);
   factor=dev->sensor.optical_res/dpihw;
 
   /* coarse gain calibration is always done in color mode */
@@ -3643,6 +3643,7 @@ gl843_init (Genesys_Device * dev)
 
   /* move head away from park position */
   gl843_feed (dev, 300);
+  usleep (100000);
 
   /* now hardware part is OK, set up device struct */
   FREE_IFNOT_NULL (dev->white_average_data);