I was trying to resize some images to 1080 x 1920 (tiff) using Image Processor but the resulting images came out as 1080 x 1620 and the filesize appears to have remained unchanged. Similarly, another time 720 x 576 came out as 720 x 540.
Have i missed something ? Can someone please help, i'm baffled.
That's perfectly normal and expected behavior.
Quite simply your images do not have the necessary aspect ratio to fill the entire pixel dimensions you're specifying. It's elementary, grade-school math.
Your images are not tall enough in the specific cases you mention.
Work out the ratio between 1080 and 1920: you'll get an aspect ratio of 1:1.77777777777778. That is exactly the aspect ratio to which you must crop your images first if you absolutely want those exact pixel dimensions (width x height).
Other than that, the image processor is working exactly as it should.
You can't fit a round peg into a square hole, so to speak.
The Image Processor Scripts use Adobe Fit Image plug-in to do the resize. It looks like you trying to resize to fit a HDTV. You should set width 1920 and the height to 1080. All image will be re-size to fit within that size pixel area. The image will retain their current Aspect Ratio and not distort. Image with a 16:9 aspect ratio will be resized 1920 px wide and 1080 px high. Image with an Aspect ratio wider then 16:9 will be resize 1920 PX width and x PX high where x is less then <1080. If an images aspect ratio is narrower then 16:9 the image will be resized x PX wide and 1080P X high where x is less the <1920.