Making a matching background

[Pito Salas]

I have an illustration from the web which has a simple multi color background. It is around 2x4 in proportion. I would like to make it a banner with around 40x4 proportion, that is, much much wider. I would like the new part of the canvas to be a seamless continuation of the background. It could be blurred or transitioned or anything else as long as it looks good. I am attaching a sample. How would i do that?

[v_kyr]

If I understand correctly what you want to do, this is not easy to do without some good working "Content Aware Scale" function like one can find in PS.

• How to resize picture without stretching it

[RNKLN]

Crop to desired dimensions; select transparent pixels (selection menu); grow selection by a few pixels (selection menu); inpaint (edit menu). 

Sometimes this gives perfect results. 

[Pito Salas]

Wow it works quite well! I had to do it in smaller steps but then for some reason the inpaint started giving me areas with transparent pixels. Do you know why?

[RNKLN]

I don't know how come. I experience the same every now and then. I apply one of multiple techniques which may or may not work:  

inpaint brush 

clone stamping

 copy one area into the empty area and finish with inpainting brush