As a point of clarification the dpi in Powerpoint does not matter, that is a printer setting so going from 96 to 300 just makes the image print the correct size.
The problem is the resizing, should not have to do that.
You should be working at the correct size in Powerpoint (3240 pixels by 2175 pixels DPI does not matter at that point), this way no pixel resizing is required.
Then once you save it as a jpg at whatever dpi from Powerpoint, open that in file in IrfanView.
Then on the resize screen only change the dpi to 300 from whatever it is and re-save it at 100% quality, that way the image is not resampled as the pixel count remains unchanged.
Here is a overview of what DPI is
LINK as it has nothing to do with quality only changing the number of pixels or compression rate will affect image quality.
As a point of clarification the dpi in Powerpoint does not matter, that is a printer setting so going from 96 to 300 just makes the image print the correct size.
The problem is the resizing, should not have to do that.
You should be working at the correct size in Powerpoint (3240 pixels by 2175 pixels DPI does not matter at that point), this way no pixel resizing is required.
Then once you save it as a jpg at whatever dpi from Powerpoint, open that in file in IrfanView.
Then on the resize screen only change the dpi to 300 from whatever it is and re-save it at 100% quality, that way the image is not resampled as the pixel count remains unchanged.
Here is a overview of what DPI is [url=http://www.hirescovers.net/forum/viewtopic.php?t=21412]LINK[/url] as it has nothing to do with quality only changing the number of pixels or compression rate will affect image quality.