Resolution

True. To make sure quality is maintained, my order would be: Levels and/or curves, straightening (if needed), cropping, sharpening.

I recently entered an online competition, where the rules asked for a 300PPI shot, which I dutifully provided. After grinding my teeth. Of course I made sure I unchecked the 'resample image' box, or the image would have been interpolated to 4x it's original size and degraded by the interpolation process!

Sorry! my two images are both 1400 x 1050 Pixels.Yours are not. And that gives a clue The two options are to constrain proportions or to resample - you can choose one and the other is not available. Yes, I want to retain the size, not the proportions; you have refrained from resampling and lost the desired size by retaining the proportions.

Either way, both my images are the same pixel dimensions, but the file sizes are different (and the image dimensions in inches, and the quality, are also different). I could spend a lot of time playing around with a number of images in different editing programs, but I have to prepare for a hospital appointment tomorrow.

Geoff

Geoff - look again at the images in the screen grabs. the 72PPI image, and the 300PPI image have the same number of pixels (1400 x 1050). They are the same image, containing the same number of pixels.

Your example stipulates a size in pixels (1400 x 1050). No mention was made of a 'document size'. The actual document size will be the output of the projector, not the 'document size tagged to the image in the computer. As long as your image is 1400 x 1050 pixels, it will look just the same as the next guys image even if your 'PPI' is wildly different, when projected to fill the screen. It will also have the same sort of file size for emailing.

Thanks Pentaxophile, I like that site you linked to, I'm going to have a good read through it, looks clearly written.

One thing about that quote above for the camera club '...8bit jpeg and at a resoution of 72 pixels/inch ((so that entries may be e-mailed)...'

Am I right in thinking that actually, the resolution of the image (72ppi or 240 ppi whatever) will make no difference whatsoever to the file size when it is saved as a jpeg (which can only be 8bit anyway). You could set your image to 200ppi and when it saved it will be the same file size as if set to 72ppi (just that the dimensions will change proportionately).

What is key to controlling to file size (to make it suitable for e-mailing) is setting the compression amount at the time of saving. Am I right in thinking this?

I know we could make our image smaller (resizing it) but we wouldn't do this for the purpose of emailing it - we would do this in order to print it out on the paper size we want.