getting resized product pictures without loading product - php

Question

Regarding the poor performances of my magento homepage (4 seconds computing before it start loading assets) i optimized my source code to go down to 1 second, by removing all the $_product->load that were in my loops.
But i'm facing another issue, i can't call the picture this way anoymore :
<img src="<?php echo $this->helper('catalog/image')->init($_product, 'image')->resize(135); ?>"
so, i began to call thumbnails
<?php echo Mage::getModel('catalog/product_media_config')->getMediaUrl($_product->getThumbnail()); ?>
but there's few points that annoys me, the 2nd call don't get a default placeholder picture if no picture is found, and the bigger problem is, all the magento's product have only a large res file, which is called if i don't upload a thumbnail for each product (note : i got 1600+ products, i'd like to avoid a manual upload for every single item)
So i have two options : getting th catalog/image helper to work without loading product, or finding a way to generate all the thumbnail with the high res pictures (i looked for an extension doing this, but i guess i'm a bad googler)
EDIT : here's the collection call
$selections_products = Mage::getModel('catalog/product')->getCollection()
->addAttributeToSelect(
array(
'name',
'special_from_date',
'special_to_date',
'thumbnail',
'image',
'couleur',
'special_price',
'url_path',
'price',
'format',
'selection_moment',
'selection_rouge',
'selection_blanc',
'selection_cdc',
'selection_champagne',
'selection_exception'
)
)
->addAttributeToFilter(array(array('attribute'=>'attribute_set_id', 'like' => '4')))
->addAttributeToFilter(
array(
array('attribute'=>'selection_moment', 'like' => '1'),
array('attribute'=>'selection_rouge', 'like' => '1'),
array('attribute'=>'selection_blanc', 'like' => '1'),
array('attribute'=>'selection_cdc', 'like' => '1'),
array('attribute'=>'selection_champagne', 'like' => '1'),
array('attribute'=>'selection_exception', 'like' => '1')
)
);
$selections_products->getSelect()->limit(32);
EDIT 2 : foreach on the collection :
<?php $i = 0;
foreach($selections_products_rouge as $_product): ?>
<?php if($i==0 || $i==4): ?>
<tr>
<?php endif; ?>
<td>
<div class="prod-resume">
<div class="thumb-wrapper">
<div class="thumb">
<div class="pic-holder">
<a href="<?php echo $_product->getProductUrl() ?>">
<img height="220" src="<?php echo Mage::getModel('catalog/product_media_config')->getMediaUrl($_product->getThumbnail()); ?>"/>
</a>
</div>
</div>
</div>
<h3 class="title"><?php echo $_product->getName(); ?></h3>
<div class="type">
<?php
$cats = $_product->getCategoryIds();
$j = 0;
foreach ($cats as $category_id) {
$_cat = Mage::getModel('catalog/category')->load($category_id);
if($_cat->getLevel() != 2 && $j < 2 && $_cat->getName() != 'Default Category'){
echo '<span>'.$_cat->getName().'</span>';
$j++;
}
}
$couleur = $_product->getResource()->getAttribute('couleur')->getFrontend()->getValue($_product);
$format = $_product->getResource()->getAttribute('format')->getFrontend()->getValue($_product);
echo '<span>'.$couleur.'</span>';
echo '<span>'.$format.'</span>';
?>
</div>
<?php echo get_promo_stamp($_product); ?>
<div class="bottom">
<?php echo get_product_price_html($_product,$_taxHelper,$_coreHelper); ?>
<div class="btns">
Fiche produit
<?php if($_product->isSaleable()): ?>
Ajouter au panier
<?php endif; ?>
</div>
</div>
Aperçu
</div>
</td>
<?php if($i==3 || $i==7): ?>
</tr>
<?php endif; ?>
<?php $i++;endforeach; ?>