Retrieving featured image's caption

I am new to WordPress and PHP.
Here is the code I have:

while( $rposts->have_posts() ) {
							$portfoliocount++;
							$rposts->the_post();
							$large_image =  wp_get_attachment_image_src( get_post_thumbnail_id(get_the_ID()), 'fullsize', false, '' );
							$large_image = $large_image[0];
							$image = portfolio_aq_resize( $large_image, $imgwidth, $imgheight, true );
							 ...
                       		<img src="<?php echo $image; ?>" alt="<?php the_title(); ?>" />
							<a href="<?php echo $large_image; ?>" title='' class="prettyPhoto[<?php echo $portfoliocount ?>]">

I need to figure out what to put in the title=” to retrieve the given attachment (featured) picture’s caption.

I have tried <php echo $large_image[‘caption’] ?> and <php echo $image[‘caption’] ?>

But it outputed h, which I think comes from the first letter of the image link (http….)

It needs to work based on the current defined variables or by defining a new variable. Existing variables cannot be modified since the rest of the code is based on them.

Any help? Thank you.

Thank you.