function image_niveaux_auto($im, $limite=1000) {

	// $limite=1000: les nuances min et max representent 0,1% du total
	
	$image = valeurs_image_trans($im, "niveaux_auto-$limite");
	if (!$image) return("");

	$x_i = $image["largeur"];
	$y_i = $image["hauteur"];
	$im = $image["fichier"];
	$dest = $image["fichier_dest"];
	$creer = $image["creer"];

	if ($creer) {
		$im = $image["fonction_imagecreatefrom"]($im);

		// Calculer les poids des differentes nuances
		for ($x = 0; $x < $x_i; $x++) {
			for ($y=0; $y < $y_i; $y++) {

				$rgb = ImageColorAt($im, $x, $y);
				$a = ($rgb >> 24) & 0xFF;
				$r = ($rgb >> 16) & 0xFF;
				$g = ($rgb >> 8) & 0xFF;
				$b = $rgb & 0xFF;

				$a = (127-$a) / 127;
				$a=1;
				
				$gris = round($a*($r+$g+$b) / 3);
				$r = round($a*$r);
				$g = round($a*$g);
				$b = round($a*$b);
								
				$val_r[$r] ++;
				$val_v[$g] ++;
				$val_b[$b] ++;
			} 
		}

		$total = $x_i * $y_i;

		// Calculer le tableau des correspondances
		// Rouge
		for ($bas_r = 0; $somme_bas_r < $total/$limite; $bas_r++) {
			$somme_bas_r += $val_r[$bas_r];
		}	
		
		for ($haut_r = 255; $somme_haut_r < $total/$limite ; $haut_r--) {
			$somme_haut_r += $val_r[$haut_r];
		}
	
		$courbe_r[0] = 0;
		$courbe_r[255] = 255;
		$courbe_r[$bas_r] = 0;
		$courbe_r[$haut_r] = 255;
	
		ksort($courbe_r);
		while (list($key, $val) = each($courbe_r)) {
			if ($key > 0) {
				$key1 = $key_old;
				$val1 = $val_old;
				$prop = ($val - $val1) / ($key-$key1);
				for ($i = $key1; $i < $key; $i++) {
					$valeur = round($prop * ($i - $key1) + $val1);
					$courbe_r[$i] = $valeur;
				}
				$key_old = $key;
				$val_old = $val;
			} else {
				$key_old = $key;
				$val_old = $val;
			}
		}

		// Bleu
		for ($bas_b = 0; $somme_bas_b < $total/$limite; $bas_b++) {
			$somme_bas_b += $val_b[$bas_b];
		}	
		
		for ($haut_b = 255; $somme_haut_b < $total/$limite ; $haut_b--) {
			$somme_haut_b += $val_b[$haut_b];
		}
	
		$courbe_b[0] = 0;
		$courbe_b[255] = 255;
		$courbe_b[$bas_b] = 0;
		$courbe_b[$haut_b] = 255;
	
		ksort($courbe_b);
		while (list($key, $val) = each($courbe_b)) {
			if ($key > 0) {
				$key1 = $key_old;
				$val1 = $val_old;
				$prop = ($val - $val1) / ($key-$key1);
				for ($i = $key1; $i < $key; $i++) {
					$valeur = round($prop * ($i - $key1) + $val1);
					$courbe_b[$i] = $valeur;
				}
				$key_old = $key;
				$val_old = $val;
			} else {
				$key_old = $key;
				$val_old = $val;
			}
		}

		// Vert
		for ($bas_v = 0; $somme_bas_v < $total/$limite; $bas_v++) {
			$somme_bas_v += $val_v[$bas_v];
		}	
		
		for ($haut_v = 255; $somme_haut_v < $total/$limite ; $haut_v--) {
			$somme_haut_v += $val_v[$haut_v];
		}
	
		$courbe_v[0] = 0;
		$courbe_v[255] = 255;
		$courbe_v[$bas_v] = 0;
		$courbe_v[$haut_v] = 255;
	
		ksort($courbe_v);
		while (list($key, $val) = each($courbe_v)) {
			if ($key > 0) {
				$key1 = $key_old;
				$val1 = $val_old;
				$prop = ($val - $val1) / ($key-$key1);
				for ($i = $key1; $i < $key; $i++) {
					$valeur = round($prop * ($i - $key1) + $val1);
					$courbe_v[$i] = $valeur;
				}
				$key_old = $key;
				$val_old = $val;
			} else {
				$key_old = $key;
				$val_old = $val;
			}
		}

		// Appliquer les correspondances
		$im2 = imagecreatetruecolor($x_i, $y_i);
		@imagealphablending($im2, false);
		@imagesavealpha($im2,true);
		$color_t = ImageColorAllocateAlpha( $im2, 255, 255, 255 , 0 );
		imagefill ($im2, 0, 0, $color_t);

		for ($x = 0; $x < $x_i; $x++) {
			for ($y=0; $y < $y_i; $y++) {
				$rgb = ImageColorAt($im, $x, $y);
				$a = ($rgb >> 24) & 0xFF;
				$r = ($rgb >> 16) & 0xFF;
				$v = ($rgb >> 8) & 0xFF;
				$b = $rgb & 0xFF;
				
				$r = $courbe_r[$r];
				$v = $courbe_v[$v];
				$b = $courbe_b[$b];
				
				$color = ImageColorAllocateAlpha( $im2, $r, $v, $b , $a );
				imagesetpixel ($im2, $x, $y, $color);			
			}
		}

		$image["fonction_image"]($im2, "$dest");
		imagedestroy($im2);
		imagedestroy($im);
	}

	$class = $image["class"];
	if (strlen($class) > 1) $tags=" class='$class'";
	$tags = "$tags alt='".$image["alt"]."'";
	$style = $image["style"];
	if (strlen($style) > 1) $tags="$tags style='$style'";
	
	return "<img src='$dest'$tags />";
}