Converting grayscale image to pure black and white

[DianaSimona]

I'm trying to convert a grayscale image to pure black and white in php using the GD library.

The purpose would be to detect the cervical cells within the image.

I'll leave the php code and a matlab one (i wrote this code in matlab and i'm trying to obtain the same result in php). Basically, im having troubles accessing each individual pixel's color and modifying it.

MATLAB:

clear all, clc, close all;


I = imread('celule.jpg');
imshow(I)
title('original');

a=rgb2gray(I);

figure;
imshow(a)
title('grayscale');

s=size(a);


for i=1:s(1)
    for j=1:s(2)

        if a(i,j)>190
            a(i,j)=0;
        else a(i,j)=255;
            end
        end
end

 figure;
 imshow(a)
 title('pure black and white');

PHP: 

<?php
 $im = imagecreatefromjpeg("celule.jpg");

function imagetograyscale($im)
{
    if (imageistruecolor($im)) {
        imagetruecolortopalette($im, false, 256);
    }

    for ($c = 0; $c < imagecolorstotal($im); $c++) {
        $col = imagecolorsforindex($im, $c);
        $gray = round(0.299 * $col['red'] + 0.587 * $col['green'] + 0.114 * $col['blue']);
        imagecolorset($im, $c, $gray, $gray, $gray);
    }
}

imagetograyscale($im);

//imagefilter($im, IMG_FILTER_CONTRAST, -255);  //i'm not looking for this effect 

header('Content-type: image/jpeg');
imagejpeg($im);

$C = imagesx($im); //width
 $L = imagesy($im); //height

 echo "Dimensiuni imagine: latime $C, inaltime $L <br>";

 //scanning through the image
 for($x = 0; $x < $L; $x++) {  //each line
    for($y = 0; $y < $C; $y++) {  //each collumn
        // pixel color at (x, y)
        $color = imagecolorat($im, $y, $x);
        $color = imagecolorsforindex($im, $color); //getting rgb values
        $RED[$x][$y] = $color["red"];  //each rgb component
        $GREEN[$x][$y] = $color["green"];
        $BLUE[$x][$y] = $color["blue"];

    }
 } 

?>

image "celule.jpg": https://i.ibb.co/6Ffj6sc/celule.jpg

[requinix]

And what's the problem? I see some PHP code there which looks like it's on the right path. In fact it already has something to grayscale an image, so I would think that what you need to do is simply modify that to use black and white instead.

[Barand]

Have you tried 

$im = imagecreatefromjpeg('../images/celule.jpg');
imagefilter($im, IMG_FILTER_GRAYSCALE);
imagefilter($im, IMG_FILTER_CONTRAST, -1000); 

header("Content-type: image/jpeg");
imagejpeg($im);
imagedestroy($im); 

Emulating you matlab example 

$im = imagecreatefromjpeg('../images/celule.jpg');
imagefilter($im, IMG_FILTER_GRAYSCALE);

$white = imagecolorallocate($im, 255,255,255);
$black = imagecolorallocate($im, 0,0,0);

$w = imagesx($im);
$h = imagesy($im);

for ($x=0; $x<$w; $x++) {
    for ($y=0; $y<$h; $y++) {
        $c = imagecolorat($im, $x, $y);
        if ($c & 0xFF > 190)                         // blue component
            imagesetpixel($im, $x, $y, $white);
        else 
            imagesetpixel($im, $x, $y, $black);
    }
}
header("Content-type: image/jpeg");
imagejpeg($im);
imagedestroy($im); 

Gives an effect like this (top-left corner of image)

[DianaSimona]

Thank you for your replies!

What i was trying to do is obtain a pure black and white image as i did in matlab (using a threshold value), but i was quite unsure on how to implement that in php.

I will try using the tips provided!

Thanks again 😀

[Barand]

Try a combination approach, increasing the contrast to reduce the noise.