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/*
* Copyright (C) 2005 - 2013 René Rebe
* (C) 2005 - 2007 Archivista GmbH, CH-8042 Zuerich
*
* This program is free software; you can redistribute it and/or modify
* it under the terms of the GNU General Public License as published by
* the Free Software Foundation; version 2. A copy of the GNU General
* Public License can be found in the file LICENSE.
*
* This program is distributed in the hope that it will be useful, but
* WITHOUT ANY WARRANTY; without even the implied warranty of MERCHANT-
* ABILITY or FITNESS FOR A PARTICULAR PURPOSE. See the GNU General
* Public License for more details.
*
* Alternatively, commercial licensing options are available from the
* copyright holder ExactCODE GmbH Germany.
*/
#include <iostream>
#include "Image.hh"
#include "Colorspace.hh"
#include "Matrix.hh"
#include "empty-page.hh"
#include "optimize2bw.hh"
/* TODO: for more accurance one could introduce a hot-spot area that
has a higher weight than the other (outer) region to more reliably
detect crossed but otherwise empty pages */
bool detect_empty_page (Image& im, double percent, int marginH, int marginV,
int* set_pixels)
{
// sanitize margins
if (marginH % 8 != 0)
marginH -= marginH % 8;
// TODO: optimize not to copy the pixel data on colorspace conversion
Image image;
image = im;
// already in sub-byte domain? just count the black pixels
if (image.spp == 1 && (image.bps > 1 && image.bps < 8))
{
colorspace_by_name (image, "gray1");
}
// if not 1-bit, yet: convert it down ...
else if (image.spp != 1 || image.bps != 1) {
// don't care about cmyk vs. rgb, just get gray8 pixels, quickly
colorspace_by_name (image, "gray8");
// force quick pass, no color use, 1px radius
optimize2bw (image, 0, 0, 128, 0, 1);
// convert to 1-bit (threshold) - optimize2bw does not perform that step ...
colorspace_gray8_to_gray1 (image);
}
// count bits and decide based on that
// create a fast bit count lookup table
int bits_set[256] = { 0 };
for (int i = 0; i < 256; i++) {
int bits = 0;
for (int j = i; j != 0; j >>= 1) {
bits += (j & 0x01);
}
bits_set[i] = bits;
}
int stride = (image.w * image.bps * image.spp + 7) / 8;
// count pixels by table lookup
int pixels = 0;
uint8_t* data = image.getRawData();
for (int row = marginV; row < image.h - marginV; ++row) {
for (int x = marginH/8; x < stride - marginH/8; ++x) {
int b = bits_set [ data[stride*row + x] ];
// it is a bits_set table - and we want the zeros ...
pixels += 8-b;
}
}
float image_percent = (float)pixels/(image.w*image.h) * 100;
if (set_pixels)
*set_pixels = pixels;
return image_percent < percent;
}
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