From 8328db4e2cb86d06938242cb5a6dc2e2147a93c5 Mon Sep 17 00:00:00 2001
From: Nick Downing <nick@ndcode.org>
Date: Mon, 8 Jan 2024 02:55:36 +1100
Subject: [PATCH] Experimental warping algorithm (command line only for now)

---
 .gitignore |   4 +++
 deps.sh    |   2 ++
 warp.py    | 100 +++++++++++++++++++++++++++++++++++++++++++++++++++++
 3 files changed, 106 insertions(+)
 create mode 100644 .gitignore
 create mode 100755 deps.sh
 create mode 100755 warp.py

diff --git a/.gitignore b/.gitignore
new file mode 100644
index 0000000..d0f62f6
--- /dev/null
+++ b/.gitignore
@@ -0,0 +1,4 @@
+/a-008_warped.png
+/a-008_warped_grid.png
+/a-009_warped.png
+/a-009_warped_grid.png
diff --git a/deps.sh b/deps.sh
new file mode 100755
index 0000000..1ee5bbe
--- /dev/null
+++ b/deps.sh
@@ -0,0 +1,2 @@
+#!/bin/sh
+pip3 install --user pygobject pycairo numpy opencv-python
diff --git a/warp.py b/warp.py
new file mode 100755
index 0000000..48fb423
--- /dev/null
+++ b/warp.py
@@ -0,0 +1,100 @@
+#!/usr/bin/env python3
+
+import cv2
+import imageio
+import numpy
+import sys
+
+EXIT_SUCCESS = 0
+EXIT_FAILURE = 1
+
+CELL_X = 32
+CELL_Y = 64
+
+# find a 3x3 matrix that takes:
+#   [x00, x01, 1] to [y00, y01, 1]
+#   [x10, x11, 1] to [y10, y11, 1]
+#   [x20, x21, 1] to [y20, y11, 1]
+#   [x30, x31, 1] to [y30, y31, 1]
+def perspective_transform(x, y):
+  A = numpy.zeros((8, 8), numpy.double)
+  b = numpy.zeros((8,), numpy.double)
+  A[:4, :2] = x
+  A[:4, 2] = 1.
+  A[:4, 6:] = -y[:, :1] * x
+  b[:4] = y[:, 0]
+  A[4:, 3:5] = x
+  A[4:, 5] = 1.
+  A[4:, 6:] = -y[:, 1:] * x
+  b[4:] = y[:, 1]
+  H = numpy.zeros((9,), numpy.double)
+  H[:8], _, _, _ = numpy.linalg.lstsq(A, b, rcond = None)
+  H[8] = 1.
+  H = numpy.reshape(H, (3, 3))
+  return H
+
+if len(sys.argv) < 2:
+  print(f'usage: {sys.argv[0]:s} file.txt')
+  sys.exit(EXIT_FAILURE)
+file_txt = sys.argv[1]
+
+in_png = ['a-008.png', 'a-009.png']
+out_png = ['a-008_warped.png', 'a-009_warped.png']
+out_png_grid = ['a-008_warped_grid.png', 'a-009_warped_grid.png']
+with open(file_txt) as fin:
+  n_pages = int(fin.readline())
+  for i in range(n_pages):
+    state = int(fin.readline())
+    nodes = numpy.loadtxt(fin, numpy.double, max_rows = 4)
+    chars = numpy.loadtxt(fin, numpy.int32, max_rows = 2)
+    H = numpy.loadtxt(fin, numpy.double, max_rows = 3)
+
+    y = numpy.array(
+      [
+        [-.5, chars[0] + .5, chars[0] + .5, -.5],
+        [-.5, -.5, chars[1] + .5, chars[1] + .5],
+        [1., 1., 1., 1.]
+      ],
+      numpy.double
+    )
+    x = numpy.linalg.solve(H, y)
+    x = (x[:2, :] / x[2:, :]).transpose()
+
+    xs = (chars[0] + 1) * CELL_X
+    ys = (chars[1] + 1) * CELL_Y
+    y = numpy.array(
+      [
+        [0., 0.],
+        [xs, 0.],
+        [xs, ys],
+        [0., ys]
+      ],
+      numpy.double
+    )
+    H = perspective_transform(x, y)
+
+    image = cv2.warpPerspective(
+      imageio.v2.imread(in_png[i]).astype(numpy.double),
+      H,
+      (xs, ys)
+    )
+    image[image < 0.] = 0.
+    image[image > 1.] = 1.
+
+    imageio.v2.imsave(
+      out_png[i],
+      numpy.round(image * 255.).astype(numpy.uint8)
+    )
+
+    # convert to RGB with grid
+    image = numpy.stack([image] * 3, 2)
+    blue = numpy.array([0., 0., 1.], numpy.double)
+    for j in range(chars[0] + 1):
+      image[:, j * CELL_X + CELL_X // 2, :] = blue[numpy.newaxis, :]
+    for j in range(chars[1] + 1):
+      image[j * CELL_Y + CELL_Y // 2, :, :] = blue[numpy.newaxis, :]
+
+    imageio.v2.imsave(
+      out_png_grid[i],
+      numpy.round(image * 255.).astype(numpy.uint8)
+    )
-- 
2.34.1