Artefacts with transparency in png drawing

[artygrand]

This is:

• [x] a bug report
• [ ] a feature request
• [ ] not a usage question (ask them on https://stackoverflow.com/questions/tagged/phpspreadsheet or https://gitter.im/PHPOffice/PhpSpreadsheet)

What is the expected behavior?

In excel I can insert png image with transparency without problems

What is the current behavior?

Problem is artefacts in transparent background, like in example below. This is one file made from 2 in Photoshop.
Absolutely opaque, with grey zones.

What are the steps to reproduce?

Please provide a Minimal, Complete, and Verifiable example of code that exhibits the issue without relying on an external Excel file or a web server:

<?php

require __DIR__ . '/vendor/autoload.php';

// Create new Spreadsheet object
$spreadsheet = new \PhpOffice\PhpSpreadsheet\Spreadsheet();

$sheet = $spreadsheet->getActiveSheet();

$stamp = MemoryDrawing::fromString($stamp_file);
$stamp->setName('Stamp');
$stamp->setHeight(120);
$stamp->setCoordinates('A2');
$stamp->setWorksheet($sheet);

$writer = new PhpOffice\PhpSpreadsheet\Writer\Xlsx($spreadsheet);
$writer->save($path);

If this is an issue with reading a specific spreadsheet file, then it may be appropriate to provide a sample file that demonstrates the problem; but please keep it as small as possible, and sanitize any confidential information before uploading.

What features do you think are causing the issue

• [ ] Reader
• [x] Writer
• [ ] Styles
• [ ] Data Validations
• [ ] Formula Calculations
• [ ] Charts
• [ ] AutoFilter
• [ ] Form Elements

Does an issue affect all spreadsheet file formats? If not, which formats are affected?

Which versions of PhpSpreadsheet and PHP are affected?

PhpSpreadsheet 1.28 PHP 8.1

[oleibman]

You do not show how you arrived at the value in $stamp_file. Please compare your code to the following:

        $stamp_file = file_get_contents('issue.3624.png'); // the file you uploaded above
        $stamp = PhpOffice\PhpSpreadsheet\Worksheet\MemoryDrawing::fromString($stamp_file);

Or, more simply (use drawing as-is rather than as memory drawing):

        $stamp = new PhpOffice\PhpSpreadsheet\Worksheet\Drawing();
        $stamp->setPath('issue.3624.png');

In either case, the result appears to be exactly the same as if I had added the drawing directly in Excel (adjusting the height appropriately). If your results differ, please show how.

Excel:

PhpSpreadsheet:

[artygrand]

@oleibman , my attachment isn't original picture, but the broken result I use it with laravel S3 Storage, so I can get only as string (I don't want to copy it on server and then wipe)

Okay, I tested different approaches and looks like found the bug. Lets try these 3 snippents

file_get_contents with storage path

$spreadsheet = new \PhpOffice\PhpSpreadsheet\Spreadsheet();
$sheet = $spreadsheet->getActiveSheet();

$stamp = PhpOffice\PhpSpreadsheet\Worksheet\MemoryDrawing::fromString(file_get_contents(storage_path('app/test.png')));
$stamp->setName('Stamp');
$stamp->setHeight(120);
$stamp->setCoordinates('A2');
$stamp->setWorksheet($sheet);

$writer = new PhpOffice\PhpSpreadsheet\Writer\Xlsx($spreadsheet);
$writer->save(storage_path('app/res-fgc.xlsx'));

Storage getter, that I use. It is almost file_get_contents

$spreadsheet = new \PhpOffice\PhpSpreadsheet\Spreadsheet();
$sheet = $spreadsheet->getActiveSheet();

$stamp = PhpOffice\PhpSpreadsheet\Worksheet\MemoryDrawing::fromString(Storage::disk('local')->get('test.png'));
$stamp->setName('Stamp');
$stamp->setHeight(120);
$stamp->setCoordinates('A2');
$stamp->setWorksheet($sheet);

$writer = new PhpOffice\PhpSpreadsheet\Writer\Xlsx($spreadsheet);
$writer->save(storage_path('app/res-stor.xlsx'));

Not memory drawing but base

$spreadsheet = new \PhpOffice\PhpSpreadsheet\Spreadsheet();
$sheet = $spreadsheet->getActiveSheet();

$stamp = new PhpOffice\PhpSpreadsheet\Worksheet\Drawing();
$stamp->setPath(storage_path('app/test.png'));
$stamp->setName('Stamp');
$stamp->setHeight(120);
$stamp->setCoordinates('A2');
$stamp->setWorksheet($sheet);

$writer = new PhpOffice\PhpSpreadsheet\Writer\Xlsx($spreadsheet);
$writer->save(storage_path('app/res-path.xlsx'));

Original picture:

Results: res-fgc.xlsx res-stor.xlsx res-path.xlsx

Drawing with path

MemoryDrawing is absolutely broken

Where is alpha channel?

[oleibman]

Thank you, I am now able to duplicate your problem. However, I believe the problem lies in Php, not in PhpSpreadsheet.

        $stamp_file = file_get_contents('issue.3624b.png'); // your new image
        $gdImage = imagecreatefromstring($stamp_file);
        imagepng($gdImage, 'issue.3624c.png');

This code snippet, which does not use PhpSpreadsheet at all, shows that its output file does not match the input file (and, in fact, matches your 'bad' image). When I substitute your original input file, the output file does match it, so I believe this code is correct, and therefore that one or both of the native Php functions imagecreatefromstring or imagepng has a problem. For the record, specifying PNG_NO_FILTER or PNG_ALL_FILTERS on the imagepng call does not change anything.

[oleibman]

I have opened an issue with Php.

[oleibman]

From the Php issue, an extra call was suggested (imagesavealpha). I will create a PR to incorporate this suggestion into PhpSpreadsheet. Look for it in a day or two.