Poor quality of GUI bakcround image?

Hi,

I load backround image to my GUI, but the quality of this image was poor when I putted it to GUI. Normally quality of this image is very good. What I do wrong or what can cause this problem?

I use following code:

ha = axes('units','normalized', 'position',[0 0 1 1]);
uistack(ha,'bottom');
I=imread('image.png');
hi = imagesc(I)
colormap gray
set(ha,'handlevisibility','off', 'visible','off')

Teemu