Slideshow low quality image

Hi.. I tried to change the position of slideshow from sidebar to the sticky post position (Top 1 widget). everything is ok except the picture shown have a very bad quality, although the original file have a good quality. I have tried to edit some code on function.php and media.php, but it doesn't work.

Hello,

Could you please provide me with a URL to your website, either here or via PM (click the “Private Message” text underneath my avatar) so that I may analyze it?