Roy, yes ppi = pixels per inch. I normally save as compressed jpeg that by default is 300ppi. I noticed that save for web comes in at 200ppi. I have never tried 72. I don't understand how 72 ppi can be better quality than 200 unless for web viewing 200 is way to much and lost detail cannot be seen.

I noticed a big file size difference when I got a 12mp camera over 6mp particularly if there is lots of fine detail. It will be interesting when cameras are 20mp, but perhaps its a lot down to me not being to genned up on file size reduction from large files without loosing detail.

Don

You've hit the nail on the head there Don. The pixel size resolution of most monitors is such that 200ppi is more detail than can be displayed. For an old CRT, then 72ppi was more than could have been displayed. I haven't bothered working out the resolution of the newest, best flat panel displays.

I have only just started trying the 72ppi setting to see the result and am quite surprised, viewing on the web there doesn't seem to be any loss in quality. The reason I thought I would give it a go is because of copyright. If it can only be seen at the 72ppi then its know use to anyone trying to use your image.

Thanks Duncan and Christine,

I will have a play and then use 72 for my next pic.

I had a good look at Roys gallery and they all seem good. :)

Don

Don, I dont think you will see any difference when viewing on the web if you use 72 ppi, 300 ppi or 1000 ppi. Neither will the image size be any different. Canon Cameras default to 72 dpi whereas my Nikon CP 4500 defaults to 300 ppi but quality wise it is irrelevent - you can change to whatever you like, file size will not be effected. The only time it makes a difference is for printing output.

Christine, DPI/PPI doesn't matter for web viewing, only for printing. If you post a image say 800 pixels wide at 72 ppi - you will get a 11.1 inch print if you use 72 dpi (poor quality print) if you print at 300 dpi you will get a 2.6 inch print size (good quality print)
Try saving a inamge at say 30 ppi, you still will not see much difference when viewing on the web.

The general opinion is that the very best monitors nowadays can display up to 90ppi - but you are talking about top quality monitors, the average will still only display around 72 ppi. If you wanting to be ultra safe you could save at 96 ppi but you would be hard pushed to see any difference.
This is why I was totally confused by Don's posting about 200 and 300 ppi.

I have just done a save from a tiff in 3 flavours all sized to 1024 at 100% for a level playing field.

300 came out at 718kb
96 came out at 717kb
save for web which is 200 came out at 650kb

The difference between save for web and the others is that it has stripped out the exif info which probably accounts for the smaller file size.

Don

Terminology error on my part I should have said DPI not ppi. :o

Don

This back up what I said Don 300 ppi and 96 ppi = the same file size. As you quite rightly say, the only reason the 200 ppi is smaller is because the exif data has been stripped. There is no difference in quality to any of these dpi sizes.