PHPOffice/PhpSpreadsheet · error · PhpOffice\PhpSpreadsheet\Writer\Exception

$bitmap: compression not supported in bitmap image.\n

Error message

$bitmap: compression not supported in bitmap image.\n

What it means

processBitmap() reads the BMP compression field and requires 0 (BI_RGB, uncompressed). RLE-compressed 4/8-bit BMPs (BI_RLE8/BI_RLE4) and any other codec are rejected because the Xls IMDATA record can only store raw pixel bytes.

Source

Thrown at src/PhpSpreadsheet/Writer/Xls/Worksheet.php:2528

            throw new WriterException("$bitmap: largest image height supported is 65k.\n");
        }

        // Read and remove the bitmap planes and bpp data. Verify them.
        $planes_and_bitcount = unpack('v2', substr($data, 0, 4));
        $data = substr($data, 4);
        if ($planes_and_bitcount === false || $planes_and_bitcount[2] != 24) { // Bitcount
            throw new WriterException("$bitmap isn't a 24bit true color bitmap.\n");
        }
        if ($planes_and_bitcount[1] != 1) {
            throw new WriterException("$bitmap: only 1 plane supported in bitmap image.\n");
        }

        // Read and remove the bitmap compression. Verify compression.
        $compression = unpack('Vcomp', substr($data, 0, 4));
        $data = substr($data, 4);

        if ($compression === false || $compression['comp'] != 0) {
            throw new WriterException("$bitmap: compression not supported in bitmap image.\n");
        }

        // Remove bitmap data: data size, hres, vres, colours, imp. colours.
        $data = substr($data, 20);

        // Add the BITMAPCOREHEADER data
        $header = pack('Vvvvv', 0x000C, $width, $height, 0x01, 0x18);
        $data = $header . $data;

        return [$width, $height, $size, $data];
    }

    /**
     * Store the window zoom factor. This should be a reduced fraction but for
     * simplicity we will store all fractions with a numerator of 100.
     */
    private function writeZoom(): void
    {

View on GitHub (pinned to 65b080eef4)

Solutions

1. Re-save the image as an uncompressed 24-bit BMP
2. Convert to PNG (compressed but supported) and use the Drawing API
3. Check the compression field before calling insertBitmap()

$compression = unpack('V', (string) file_get_contents($path, false, null, 30, 4))[1];
if ($compression !== 0) {
    // re-encode uncompressed via GD
    $im = imagecreatefrombmp($path);
    imagebmp($im, $path); // GD writes uncompressed 24-bit BMP
}
$worksheetWriter->insertBitmap($row, $col, $path);

When it happens

Trigger: insertBitmap() with an RLE-compressed BMP, commonly produced when saving 8-bit palette images with compression enabled.

Common situations: Disk-space-conscious legacy pipelines that RLE-compress BMPs; images processed through older Windows imaging APIs.

Related errors

• Couldn't import $bitmap
• $bitmap doesn't contain enough data.\n
• $bitmap isn't a 24bit true color bitmap.\n
• $bitmap doesn't appear to be a valid bitmap image.\n
• $bitmap: largest image width supported is 65k.\n

AI-assisted analysis of PHPOffice/PhpSpreadsheet@65b080eef4 (2026-08-17). Data as JSON: /api/errors/10620ae026895463. Report an issue: GitHub.