memory management and images

I seem to be missing something when resizing images...

My app has a table view using custom cells with multiple labels and images. The custom cell initWithFrame allocs the labels and UIImageViews, adds them as subviews and then releases. The custom cell layout function sets the frame for each of the UIImageViews, not big as there are four images covering only half the width of the cell. My cellForRowAtIndexPath checks for any existing image (within each image view), releases it if it is there and assigns the appropriate new one into the image view. My actual image files are large, as they are designed for full screen display on another view, so effectively I'm mimicking a thumbnail type display. I thought the fact that I'd restricted the frame on each UIImageView would ensure that only a small amount of memory would be used for each one. Yet when the app first shows the table view, 6 rows with a total of 11 images, I get a memory warning from the iPad.

Example photo album style apps I've seen seem to do something similar, they don't use a separate file with a small version of the image. Any suggestions on what I am doing wrong which is gobbling up memory?

Any assistance much appreciated!