i want to reduce the file size at converted gif

[Guest]

I use the fallowing option
"nconvert -out gif -o %.gif -ratio -resize 120 90 -colors 256 *.jpg"
I convert two jpg file 1.jpg and 2.jpg
i get two output gif 1.gif and 2.gif
problem is 1.gif and 2.gif have the same width and height and the same colors .but i got the diffrent file size ?what problem cause?could anybody help me?

[xnview]

I use the fallowing option
"nconvert -out gif -o %.gif -ratio -resize 120 90 -colors 256 *.jpg"
I convert two jpg file 1.jpg and 2.jpg
i get two output gif 1.gif and 2.gif
problem is 1.gif and 2.gif have the same width and height and the same colors .but i got the diffrent file size ?what problem cause?could anybody help me?

1.jpg & 2.jpg are not the same picture...

[helmut]

problem is 1.gif and 2.gif have the same width and height and the same colors .but i got the diffrent file size ?what problem cause?could anybody help me?

The format GIF and other graphic formats use compression to reduce file size. The compression depends very much on the image contents, e.g. for GIF (LZW) compression works very well on images with little change and few colours in it, whereas images with lots of details don't compress that well and will result in larger files - even if width & height & colour depth is the same as the other image.