Perhaps the image is scaled for the nexus 7 device due to where you put it in your res/drawable .
Try moving the image to the res/drawable-xhdpi and try again, it will reduce the image a bit, and not to the Nexus 7 display (Nexus 7 tvdpi display , while I consider the two galaxy devices that you use are mdpi , so the image may not scale for them if you already place it in the mdpi folder.)
In addition to what @ Qw4z1 says about using images that are too large, that's for sure. Try to create resources of different sizes for each available density folder and from there, much more efficiently, and also lead to a reduction in the size of the .apk file.
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