Image compression without changing content format (png, jpeg, gif, webp)

Question

The difference from this question to duplicates: keep the content format (png, jpeg, gif, webp), in order not to harm images with layers, transparency, etc. The others do not have.

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I have a file upload script, where I save the file to a folder, and write the address to the database:

if (!empty($_FILES['anexo']['name']) && ($fass[0]['status'] != 'C' && $fass[0]['status'] != 'F'))
{
        $arqNome = $_FILES['anexo']['name'];
        $extpat  = pathinfo($_FILES['anexo']['name']);
        $ext     = $extpat['extension'];

        $uploaddir  = $_SERVER['DOCUMENT_ROOT'].'/sys/files/';
        $uploadfile = $tId . '-' . time();
        $uploadatt  = $uploaddir . $uploadfile . '.' . $ext;

        if (move_uploaded_file($_FILES['anx']['tmp_name'], $uploadatt)) 
        {
            $dir = str_replace('\\', '\\\\', $uploaddir);
            $arq = $uploadfile;
            $att = $arq . '.' . $ext; // $dir

            if ($attc -> attachments($tId,$arqNome,$att,$solicitante))
            {
                header('location:../t_vis.php?id='. $tId);
            }
        }
}

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I’ve been checking, and there are attachments images who are very large.

I would like to "compress/decrease" the image, as for example Whatsapp does, but of course, without losing the image quality, maintaining file type (jpg, png, etc), so does not "spoil" the original image with the loss of layers, transparency, etc.

• There are native functions for this purpose?
• There are libraries?
• There are other ways?

Answer 1

Just use for each image the functions for each format:

For PNG

• imagecreatefrompng
• imagepng

For JPEG

• imagecreatefromjpeg
• imagejpeg

To GIF

• imagecreatefromgif
• imagegif

For WEBP (requires PHP 5.4+)

• imagecreatefromwebp
• imagewebp

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There are other clear formats, such as BMP and WBMP, but they are not good formats to work with WEB, since it usually has no compression which makes a simple image very heavy.

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Working without losing transparency

Use imagecreatefrompng can cause loss of transparence, so to avoid loss use:

imagealphablending (resource $image , true);
imagesavealpha (resource $image , true);

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An example of code to reduce images with PHP in different formats

Following the example of calculating the @Bacchus:

<?php
function image_resize($path, $width = 200, $height = 200, $save = null, $quality = 100)
{
    $details = getimagesize($path);

    if (!$details) {
        trigger_error('Imagem inválida');
        return false;
    }

    $width_orig = $details[0];
    $height_orig = $details[1];

    // Calculando a proporção
    $ratio_orig = $width_orig / $height_orig;

    if ($width / $height > $ratio_orig) {
        $width = $height * $ratio_orig;
    } else {
        $height = $width / $ratio_orig;
    }

    if (is_string($save) === false) {
        $save = null;
        header('Content-Type: ' . $details['mime']);
    }

    $image_p = imagecreatetruecolor($width, $height);

    switch ($details['mime']) {
        case 'image/jpeg':
            $image = imagecreatefromjpeg($path);
            break; 
        case 'image/gif': 
            $image = imagecreatefromgif($path);
            break; 
        case 'image/png': 
            $image = imagecreatefrompng($path);
            break;
        case 'image/webp': 
            $image = imagecreatefromwebp($path);
            break;
        default:
            trigger_error('Formato não suportado');
            $image_p = null;
            return false;
    }

    imagecopyresampled($image_p, $image, 0, 0, 0, 0, $width, $height, $width_orig, $height_orig);

    if ( in_array($details['mime'], array('image/png', 'image/webp')) ) {
        imagealphablending($image_p, true);
        imagesavealpha($image_p, true);
    }

    switch ($details['mime']) {
        case 'image/jpeg':
            imagejpeg($image_p, $save, $quality);
            break; 
        case 'image/gif': 
            imagegif($image_p, $save);
            break; 
        case 'image/png': 
            imagepng($image_p, $save, $quality);
            break;
        case 'image/webp': 
            imagewebp($image_p, $save, $quality);
            break;
    }
}

Example of using to copy a JPEG image to a new smaller one:

image_resize('bar.jpg', 200, 200, 'bar_1.jpg');

To overwrite an image just use the same name:

image_resize('bar.jpg', 200, 200, 'bar.jpg');

The first 200 would be the maximum width, and the second is the maximum height.