utils: raspberrypi: ctt: Add a maximum gain parameter for LSC

A max_gain parameter is added to the config file which we pass to the
lens shading calibration. This clamps the maximum luminance gain that
gets written into the tuning files so as to prevent overflows.

It is particularly useful for lenses that cut off the light completely
from the sensor corners, and allows usable tables to be generated for
them.

Signed-off-by: David Plowman <david.plowman@raspberrypi.com>
Reviewed-by: Naushir Patuck <naush@raspberrypi.com>
Tested-by: Naushir Patuck <naush@raspberrypi.com>
Acked-by: Kieran Bingham <kieran.bingham@ideasonboard.com>
Signed-off-by: Kieran Bingham <kieran.bingham@ideasonboard.com>

utils/raspberrypi/ctt/ctt.py

@@ -269,7 +269,7 @@ class Camera:
     colour channel seperately, and then partially corrects for vignetting.
     The extent of the correction depends on the 'luminance_strength' parameter.
     """
-    def alsc_cal(self, luminance_strength, do_alsc_colour, grid_size):
+    def alsc_cal(self, luminance_strength, do_alsc_colour, grid_size, max_gain=8.0):
         if 'rpi.alsc' in self.disable:
             return 1
         print('\nStarting ALSC calibration')
@@ -292,7 +292,7 @@ class Camera:
         call calibration function
         """
         plot = "rpi.alsc" in self.plot
-        alsc_out = alsc_all(self, do_alsc_colour, plot, grid_size)
+        alsc_out = alsc_all(self, do_alsc_colour, plot, grid_size, max_gain=max_gain)
         cal_cr_list, cal_cb_list, luminance_lut, av_corn = alsc_out
         """
         write output to json and finish if not do_alsc_colour
@@ -705,11 +705,13 @@ def run_ctt(json_output, directory, config, log_output, json_template, grid_size
     alsc_d = get_config(configs, "alsc", {}, 'dict')
     do_alsc_colour = get_config(alsc_d, "do_alsc_colour", 1, 'bool')
     luminance_strength = get_config(alsc_d, "luminance_strength", 0.8, 'num')
+    lsc_max_gain = get_config(alsc_d, "max_gain", 8.0, 'num')
     blacklevel = get_config(configs, "blacklevel", -1, 'num')
     macbeth_d = get_config(configs, "macbeth", {}, 'dict')
     mac_small = get_config(macbeth_d, "small", 0, 'bool')
     mac_show = get_config(macbeth_d, "show", 0, 'bool')
     mac_config = (mac_small, mac_show)
+    print("Read lsc_max_gain", lsc_max_gain)
 
     if blacklevel < -1 or blacklevel >= 2**16:
         print('\nInvalid blacklevel, defaulted to 64')
@@ -750,7 +752,7 @@ def run_ctt(json_output, directory, config, log_output, json_template, grid_size
             Cam.json['rpi.black_level']['black_level'] = Cam.blacklevel_16
         Cam.json_remove(disable)
         print('\nSTARTING CALIBRATIONS')
-        Cam.alsc_cal(luminance_strength, do_alsc_colour, grid_size)
+        Cam.alsc_cal(luminance_strength, do_alsc_colour, grid_size, max_gain=lsc_max_gain)
         Cam.geq_cal()
         Cam.lux_cal()
         Cam.noise_cal()

utils/raspberrypi/ctt/ctt_alsc.py

@@ -13,7 +13,7 @@ from mpl_toolkits.mplot3d import Axes3D
 """
 preform alsc calibration on a set of images
 """
-def alsc_all(Cam, do_alsc_colour, plot, grid_size=(16, 12)):
+def alsc_all(Cam, do_alsc_colour, plot, grid_size=(16, 12), max_gain=8.0):
     imgs_alsc = Cam.imgs_alsc
     grid_w, grid_h = grid_size
     """
@@ -24,7 +24,7 @@ def alsc_all(Cam, do_alsc_colour, plot, grid_size=(16, 12)):
     list_cb = []
     list_cg = []
     for Img in imgs_alsc:
-        col, cr, cb, cg, size = alsc(Cam, Img, do_alsc_colour, plot, grid_size=grid_size)
+        col, cr, cb, cg, size = alsc(Cam, Img, do_alsc_colour, plot, grid_size=grid_size, max_gain=max_gain)
         list_col.append(col)
         list_cr.append(cr)
         list_cb.append(cb)
@@ -118,7 +118,7 @@ def alsc_all(Cam, do_alsc_colour, plot, grid_size=(16, 12)):
 """
 calculate g/r and g/b for 32x32 points arranged in a grid for a single image
 """
-def alsc(Cam, Img, do_alsc_colour, plot=False, grid_size=(16, 12)):
+def alsc(Cam, Img, do_alsc_colour, plot=False, grid_size=(16, 12), max_gain=8.0):
     Cam.log += '\nProcessing image: ' + Img.name
     grid_w, grid_h = grid_size
     """
@@ -153,9 +153,12 @@ def alsc(Cam, Img, do_alsc_colour, plot=False, grid_size=(16, 12)):
         median blur to remove peaks and save as float 64
         """
         cr = cv2.medianBlur(cr, 3).astype('float64')
+        cr = cr/np.min(cr)  # gain tables are easier for humans to read if the minimum is 1.0
         cb = cv2.medianBlur(cb, 3).astype('float64')
+        cb = cb/np.min(cb)
         cg = cv2.medianBlur(cg, 3).astype('float64')
         cg = cg/np.min(cg)
+        cg = [min(v, max_gain) for v in cg.flatten()]  # never exceed the max luminance gain
 
         """
         debugging code showing 2D surface plot of vignetting. Quite useful for
@@ -179,7 +182,7 @@ def alsc(Cam, Img, do_alsc_colour, plot=False, grid_size=(16, 12)):
             # print(Img.str)
             plt.show()
 
-        return Img.col, cr.flatten(), cb.flatten(), cg.flatten(), (w, h, dx, dy)
+        return Img.col, cr.flatten(), cb.flatten(), cg, (w, h, dx, dy)
 
     else:
         """
@@ -189,6 +192,7 @@ def alsc(Cam, Img, do_alsc_colour, plot=False, grid_size=(16, 12)):
         cg = np.reshape(1/g, (grid_h, grid_w)).astype('float32')
         cg = cv2.medianBlur(cg, 3).astype('float64')
         cg = cg/np.min(cg)
+        cg = [min(v, max_gain) for v in cg.flatten()]  # never exceed the max luminance gain
 
         if plot:
             hf = plt.figure(figssize=(8, 8))

utils/raspberrypi/ctt/ctt_config_example.json

@@ -3,7 +3,8 @@
   "plot": [],
   "alsc": {
     "do_alsc_colour": 1,
-    "luminance_strength": 0.5
+    "luminance_strength": 0.8,
+    "max_gain": 8.0
   },
   "awb": {
     "greyworld": 0
@@ -13,4 +14,4 @@
     "small": 0,
     "show": 0
   }
-}
+}