Hi!!
Thank you for your question about UPSIZING images. You were asking, how come that if you resize a small image to a larger one, the quality decreases. Or, if I say it with other words - the resolution increases (larger file in pixels) but the quality of the image stays the same or even decreases (visually).
Well, let me give you some information about image formats. The thing is, that jpg is copressed image format. That means, that when you were saving your image (or your camera was), you were making all the effort to make it smaller in byte size. You have put some much effort in this (again, or the camera or your software did), that you agreed to let out all the not-necessary information out of the image. Only the information that you can still see with your eye at current resolution and file size in pixels should stay in the image. That is how jpg works - it compresses the file in a way that the change to your eye is almost invisible, but the change in file size in bytes is evident.
OK, now you have the JPG that is small and nice. And now you have decided that you want to upsize (resize to a larger size) that same image. Sure, there are programs that can do that, but hey! All the extra information in the image is gone! You compressed the image! And while compressing you have decided to erase all the information that you can not see with your eye. But when you are resizing the image, and if you want the quality to stay the same, you have to have some extra information somewhere that exists in the image, but you didn't see it with your eye. And yes, you are right, that information is gone. If you still resize the image to a larger pixels size, the quality will seem much worse. That is just because there is same amount of information in a larger picture.
I hope I didn't complicate things too much and that you are still following. What I wanted to write really, was that it is normal that the image will get worse when you are trying to resize it to a biger size. There are some programs that quarantee you that they will do just that with your jpg files, but the results are not as good as their marketing is.
So, what to do? Try to find the pictures in their original size instead of trying to resize them from small files. If that is not an option, I'm afraid you'll have to live with either small imager of large images of worse quality.
Miha.
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