Resolution Question

I have a friend down under, that has sent me some shots taken with her Canon 1000D. The first version she sent were a mere 61 KB 800 x 533 and 72 PPI.

I was able to get a copy of the original shot and it's 1.41 MB, 3888 x 2592 but still only 72 PPI.

Based on my research, this camera at Large/Fine should produce a file size of 3.8 MB's, 3888 x 2892. Why is her file size so small and why is the PPI so low?

Bob

She has resized the first one. Depending on what is in the shot, the compressed size of the file (I am assuming she sent a JPG) will vary. Large expanses of the same color, for example, will compress better. The amount of compression sellected will also affect the final JPG size.

The PPI has no usefullness unless you send it to a printer.

The ppi has absolutely no meaning even for a printer (which works in dpi anyhow). Some software has simply assigned (assigned not converted not resampled nothing just given it a number) this number as 72 ppi was a number that computer monitors used to use sometimes. If you took the ppi (pixels per inch) and divided the resolution by this you will find that the print is displaying at 54 inches by 26 inches, with those numbers.

If the camera originally took some larger pixel dimensions 2892 vs 2592 then something was cropped out (or possible one dimension was resampled down in which case things would look squashed as only one side was changed). An 11 mpixel image has become a 10 mpixel image.

The very small image (800 x 533) was resampled down to make the file smaller. It's aspect ratio the same as the larger file (3888 X 2592) sent to you 1:1.5 which is the standard aspect ration of a DSLR. That suggests to me that no cropping was done, although an aspect ration of 1:1.34 may be used by some cameras.


BTW I have two images on my desktop one has been assigned 3 ppi the other 300 ppi, my OS does not even care about those numbers as both images preview the same since they are the same pixel dimensions. If I send them to my printer it will not care either.

So because she took the shot in jpg, her camera did some form of compression to get it to the 1.4 MB size but and outside of her shooting in RAW, this is the best she could get from her camera. Do I have that right?

I have always wondered about that PPI thing so thanks for the explanation.

Bob

Right. Jpeg is a lossy comression method and has various settings as to how aggressive it will compress. RAW will compress (which is why higher ISO files are larger) as well but it is loseless.

bianson wrote in post #9518293
So because she took the shot in jpg, her camera did some form of compression to get it to the 1.4 MB size but and outside of her shooting in RAW, this is the best she could get from her camera. Do I have that right?

I have always wondered about that PPI thing so thanks for the explanation.

Bob

The compression can be set in the camera as well, she may have one of the lower quality settings set on it.