Refactor Magento 1 Additional Images Into Magento 2 Suitable Format

images_refactor.php

<?php
/*
* USING EXCEL
* 1) Grab the export from Magento
* 2) Filter the blanks out of "_media_image" column 
* 3) Copy columns sku	image, small_image, thumbnail, _media_image into new sheet
* 4) Save it in same directory as this script and run.
* 5) Refactored feed will be generated.
*/
?>
<style>
    td {
        border-bottom: 1px solid #ccc;}
    td.found {background-color:#00ff00;}
    td.nofound {background-color:#ff0000;}
</style>
<?php
function readCSV($csvFile){
    $file_handle = fopen($csvFile, 'r');
    while (!feof($file_handle) ) {
        $line_of_text[] = fgetcsv($file_handle, 0);
    }
    fclose($file_handle);
    return $line_of_text;
}


$csvOut = "sku,media_gallery\n";
const ADDR = "https://your.magento1.website/media/catalog/product"; //Media folder

$csv = readCSV('images.csv'); // Make sure this exists or you will have a forever error log.
//echo "<table><th>SKU</th><th>Conf</th>";
$counter = 0;

$csvArray = array();
array_push($csvArray,array("sku","base_image","small_image","thumbnail_image","additional_images"));
$lastSku = "";
foreach ( $csv as $c ) {
    echo "<tr>";
    if($counter > 0) {

        //$sku = $c[0];
        if($c[0] != ""){
            $sku = $c[0];
        }

        $img = ADDR . $c[4]; //Additional Image


        //echo $sku . ".....";
        //echo $img . "<br /><hr />";
//        echo "<td>";

        if($sku != $lastSku) { //We're on a new one

            array_push($csvArray, array($lastSku, $b_img, $s_img, $t_img, implode(",", $confArray)));
            $confArray = array();
        }

        //$confArray = array();
        //need to try and bypass pesky duplicates
        if($c[0]!="") { //The additional image is on the same line as the sku
            $curr_arr = array($c[1], $c[2], $c[3]);
            if (!in_array($c[4], $curr_arr)) {
                array_push($confArray, $img); //Push the additional shit
            }
        }else{
            $curr_arr = array($b_img, $s_img, $t_img);
            if (!in_array($img, $curr_arr)) {
                array_push($confArray, $img); //Push the additional shit
            }
        }


        if($c[1]!= "") { //Base image
            $b_img = ADDR . $c[1];
        }
        if($c[2]!= "") { //Small Image
            $s_img = ADDR . $c[2];
        }
        if($c[3]!= "") { //Thumbnail
            $t_img = ADDR . $c[3];
        }
        $lastSku = $sku;
    }
    $counter++;
//    echo "</tr>";
}


?>
<!--</table>-->
<?php

$csv_handler = fopen ('images_processed.csv','w');

foreach($csvArray AS $toGo){
    if($toGo[0] != "") {
        fputcsv($csv_handler, $toGo);
    }
}
fclose ($csv_handler);


foreach($csvArray AS $toGo){
    echo $toGo[0] . "......" . $toGo[1] . "<br />";
}

Here's my gist for configurable products/super attributes - https://gist.github.com/thomas-harding/b4527534eaf3e3e57c6e1f8be329d973

I wanted to paste this here because it could be very useful to those who need to migrate Magento 1 products without using the migration tool. I usually use Firebear Import/Export for this purpose, but it might be useful for other platforms.

I know it's not perfect by any standards (and more experienced PHP coders could create a tool to do everything all in one), but if this saves 1 developer even an hour of their time, then this gist was worth creating.