This is how it appears on your website. Its a PNG file 1024x543px at 467K. You brought it down to 456x232 which isn't in proportion to original size. Though you gave it smaller dimensions the download size remains at 467K.

SIZE: 467K

This is reduced in proportion down to 456x241 using antenna razor. Its still a transparent PNG file but now only 107K because its the exact size.

SIZE: 107K

This is a JPG file with a black background reduced in proportion down to 456x241 using an imaging program. It is only 27K! 

SIZE: 27K

See the distortion in the icon titles and corners of phone... this is because of the ratio not being proportionate when you down sized it.  it should be 456x241

not 456x232