Different quality of images taken with imread and VideoCapture

edit

Basically I have a list of images

img00001.jpg
img00002.jpg
...

So I can easly read them with VideoCapture cap("img%05d.jpg");

The strange thing is that if i read those same image with imread("img00001.jpg",CV_LOAD_IMAGE_COLOR);

I may get a lower quality with imread

Do you know why?