Small image is bigger then normal image

Little explanition: I am using the CK Slider on a site in development.
I have choosen some images, all in the following size: 980 x 550 pixels.
This works perfect, on screen as on smartphone.
But when I upload an image that as half this size (so 490 x 550 pixels) the image is resized to 980 x 550 pixels.
the thing I want to know: is it possible to use smaller images then the maximum size without the images being resized? Or is it better to make a blank page of 980 x 550 pixels and to place the image on this page and then upload this page?

Please, can you help me with this issue?

Hi
the best is to have the same dimensions for all images.You can try the option "adjust image", if yes it will use the height of the image as max value and keep the width ratio
CEd

Hi CEd,

Thanks for your reply.
Unfortunately this is not the solution.
Right now I have chosen the "adjust image"but there are now 2 white lines appearring on either side and no matter I try to adjust: they will nos dissappear.
Is there a solution for this? I fill that we are almost there.

give me your url to check

Can you give me your contact details?

Hi CEd,

Sending your contact details is not neede anymore.
I was searching through your forum and found a topic of 17 Februar 2014 ( forum.joomlack.fr/index.php/15-slideshow-ck/7589-resize-images ).
After some calculation, I found out that my percentage must be 56.1% and now all is fine.

Thanks anyway and keep up the good work!!