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// Copyright 2020 Nick White.
// Use of this source code is governed by the GPLv3
// license that can be found in the LICENSE file.
// splittable is an experimental program to split a table into
// individual cells suitable for OCR
package main
import (
"flag"
"fmt"
"image"
"image/draw"
_ "image/jpeg"
"image/png"
"log"
"os"
"rescribe.xyz/integralimg"
)
const usage = `Usage: splittable [-t thresh] [-w winsize] inimg outbase
splittable is an experimental program to split a table into individual
cells suitable for OCR. It does this by detecting lines. At present it
just detects vertical lines and outputs images for each section
between those lines.
`
// returns the proportion of the given window that is black pixels
func proportion(i integralimg.Image, x int, size int) float64 {
w := i.GetVerticalWindow(x, size)
return w.Proportion()
}
// findbestvline goes through every vertical line from x to x+w to
// find the one with the lowest proportion of black pixels.
func findbestvline(img integralimg.Image, x int, w int) int {
var bestx int
var best float64
if w == 1 {
return x
}
right := x + w
for ; x < right; x++ {
prop := proportion(img, x, 1)
if prop > best {
best = prop
bestx = x
}
}
return bestx
}
// findvlines finds vertical lines, returning an array of x coordinates
// for each line. It works by moving a window of wsize across the image,
// marking each place where there is a higher proportion of black pixels
// than thresh.
func findvlines(img integralimg.Image, wsize int, thresh float64) []int {
maxx := img.Bounds().Dx() - 1
var lines []int
for x := 0; x < maxx-wsize; x+=wsize {
if proportion(img, x, wsize) >= thresh {
l := findbestvline(img, x, wsize)
lines = append(lines, l)
}
}
return lines
}
func drawsection(img *image.Gray, x1 int, x2 int) *image.Gray {
b := img.Bounds()
width := x2-x1
new := image.NewGray(image.Rect(0, b.Min.Y, width, b.Max.Y))
for x := 0; x < width; x++ {
for y := b.Min.Y; y < b.Max.Y; y++ {
new.SetGray(x, y, img.GrayAt(x1 + x, y))
}
}
return new
}
func main() {
flag.Usage = func() {
fmt.Fprintf(flag.CommandLine.Output(), usage)
flag.PrintDefaults()
}
thresh := flag.Float64("t", 0.85, "Threshold for the proportion of black pixels below which a window is determined to be a line. Higher means fewer lines will be found.")
wsize := flag.Int("w", 1, "Window size for mask finding algorithm.")
flag.Parse()
if flag.NArg() < 2 {
flag.Usage()
os.Exit(1)
}
f, err := os.Open(flag.Arg(0))
defer f.Close()
if err != nil {
log.Fatalf("Could not open file %s: %v\n", flag.Arg(0), err)
}
img, _, err := image.Decode(f)
if err != nil {
log.Fatalf("Could not decode image: %v\n", err)
}
b := img.Bounds()
gray := image.NewGray(image.Rect(0, 0, b.Dx(), b.Dy()))
draw.Draw(gray, b, img, b.Min, draw.Src)
integral := integralimg.NewImage(b)
draw.Draw(integral, b, gray, b.Min, draw.Src)
vlines := findvlines(*integral, *wsize, *thresh)
for i, v := range vlines {
fmt.Printf("line detected at x=%d\n", v)
if i+1 >= len(vlines) {
break
}
section := drawsection(gray, v, vlines[i+1])
fn := fmt.Sprintf("%s-%d.png", flag.Arg(1), v)
f, err = os.Create(fn)
if err != nil {
log.Fatalf("Could not create file %s: %v\n", fn, err)
}
defer f.Close()
err := png.Encode(f, section)
if err != nil {
log.Fatalf("Could not encode image %s: %v\n", fn, err)
}
}
// TODO: find horizontal lines too
// TODO: do rotation
// TODO: output table cells
// TODO: potentially send cells straight to tesseract
}
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