picture quality

[willis_927]

This might be a dumb question, but here it is.. When I save the pictures I take for people, I have a high res, and a low res file or each photo. The high res picture, is say, 5 MB, and the low res is say 400KB. The thing that gets me is it I set the large file (5MB pic) to save as desktop background, its very grainy, Where as the low res (400KB file) is much more clear. Obviously I am doing something very wrong here. Any tips/help here?

 

[enzodm]

Is it the same picture saved with two different options? One reason could be the smaller one has exactly the screen resolution, so is not being modified by the operating system, while the other is converted to the low resolution of the screen by some bad internal algorithm. What if you look at them with a viewer?

 

[clarnibass]

I'm completely clueless about this so just a wild guess... maybe the background photo can't be as big as 5mb so it automatically reduces the quality to make it smaller? Probably wrong but just a guess.

 

[willis_927]

Basically, when I finish the edit, I save the picture in max quality, or near max, and place it in one folder. And then I save it again in a differnt folder as a low quality.

 

[KmH]

Resolution is the pixel dimensions of the image, not the file size.

 

[willis_927]

when you save the picture in either high or low quality, are you not changing the pixel dimensions?

 

[KmH]

No, you are not changing the pixel dimensions, only the file size.

A photo saved at high quality is the same size on a display as a photo saved at low quality.

 

[willis_927]

What about when printed?

 

[KmH]

As an example: A photo that has pixel dimensions of 3000 x 2000 pixels assigned to 100 PPI (pixels per inch) will be a 30 x 20 inch print, regardless the file size determined by the JPEG quality setting.

The same 3000 x 2000 pixel photo assigned 200 PPI will be a 15x10 inch print, and the same 3000 x 2000 pixel photo assigned 300 PPI will be a 10 x 6.66 inch print.

For the 3000 pixel side, but the math is the same for the 2000 pixel side:

3000 px divided by 100 PPI (pixels per inch)= 30 inches (in the equation the pixel units cancel, leaving only inches as the units)
3000 px divided by 200 ppi = 15 inches
3000 px divided by 300 PPI = 10 inches.

 

[enzodm]

Kmh definition is right, but there is still no explanation of the original problem. If you put two pictures in some place we can look at them.