Fix Product Image Not Changing on Color Selection in Magento 1.9

For your use you can create product in either of below format

1. Simple Product with Custom Options(size and color)

2. Configurable Product

You better go with configurable product. This is because configurable products are actually intended to use for these type of situations. The same can obtain using custom options. However there are some limitations for that. When consider management of stock, inventory etc, configurable product is much reliable than any other options in this case.

So in my opinion, you go with configurable products.

I solved this problem by calling Varien_Image::keepTransparency(true) on the before it does the resize.

Unfortunately, there's no event we can observe here, so we have to extend/override Mage_ConfigurableSwatches_Helper_Productimg::_resizeSwatchImage.

Maybe someone else (you?) can propose a more future-proof solution.

etc/config.xml:

<?xml version="1.0"?>
<config>
    <modules>
        <YourNamespace_Transparentswatch>
            <version>0.1.0</version>
        </YourNamespace_Transparentswatch>
    </modules>
    <global>
        <helpers>
            <configurableswatches>
                <rewrite>
                    <productimg>YourNamespace_Transparentswatch_Helper_Productimg</productimg>
                </rewrite>
            </configurableswatches>
        </helpers>
    </global>
</config>

Helper/Productimg.php:

<?php
class YourNamespace_Transparentswatch_Helper_Productimg extends Mage_ConfigurableSwatches_Helper_Productimg
{

    /**
     * Performs the resize operation on the given swatch image file and returns a
     * relative path to the resulting image file
     *
     * @param string $filename
     * @param string $tag
     * @param int $width
     * @param int $height
     * @return string
     */
    protected function _resizeSwatchImage($filename, $tag, $width, $height)
    {
        // Form full path to where we want to cache resized version
        $destPathArr = array(
            self::SWATCH_CACHE_DIR,
            Mage::app()->getStore()->getId(),
            $width . 'x' . $height,
            $tag,
            trim($filename, '/'),
        );

        $destPath = implode('/', $destPathArr);

        // Check if cached image exists already
        if (!file_exists(Mage::getBaseDir(Mage_Core_Model_Store::URL_TYPE_MEDIA) . DS . $destPath)) {
            // Check for source image
            if ($tag == 'product') {
                $sourceFilePath = Mage::getSingleton('catalog/product_media_config')->getBaseMediaPath() . $filename;
            } else {
                $sourceFilePath = Mage::getBaseDir(Mage_Core_Model_Store::URL_TYPE_MEDIA)
                    . DS . self::SWATCH_FALLBACK_MEDIA_DIR . DS . $filename;
            }

            if (!file_exists($sourceFilePath)) {
                return false;
            }

            // Do resize and save
            $processor = new Varien_Image($sourceFilePath);

            // Begin additions by YourNamespace_Transparentswatch module.
            $processor->keepTransparency(true);
            // End additions by YourNamespace_Transparentswatch module.

            $processor->resize($width, $height);
            $processor->save(Mage::getBaseDir(Mage_Core_Model_Store::URL_TYPE_MEDIA) . DS . $destPath);
            Mage::helper('core/file_storage_database')->saveFile($destPath);
        }

        return $destPath;
    }


}