Hi photosnob,
I'd like to add to Tom's excellent advice, and to just explain those dialogs for you.
If you take the 'Width' and 'Height' values first this tells you the image dimensions in pixels.
If you then look at the 'Resolution' and divide it into either the width or height it will tell you how physically big the image will print at on the paper.
[ATTACH]47843[/ATTACH]
An A4 piece of paper is 8.268" wide by 11.692" high.
Your original values look fine to me:
@150dpi a 1221 x 1607px image will print out @ 8.14" wide, and 10.713" high.
This WILL fit on a piece of A4.....just!
On the other hand your amended values do not work:
@300dpi a 2550 x 3650px image will print out @ 8.5" wide, and 12.167" high.
This WILL NOT fit on a piece of A4 paper.
In your case, I don't think up-scaling is needed, in fact its generally frowned upon to change the amount of pixels in an image because of the impact it has on quality....up-scaling 'adds' pixels to an image (which have to be 'guessed', ...bicubic, bilinear, etc.) and down-scaling removes pixels from the image resulting in loss of detail.
Its not always avoidable but should be as a priority.
If changing the amount of pixels in an image is dismissed this leaves only two other values that can be changed to get the right output size....the document size itself, or the dpi.
If the document size is OK, which in this case it is....just, then that leaves only one thing....the dpi.
When you say 'The original pictures only have 150dpi' this doesn't really ring true, the dpi is not 'fixed' to an image and can be whatever you want, but of course it needs to be of a value that gives you an output size that will fit the paper in the printer.
So to sum up, look at those three values,(px dimensions, document size and dpi), as being a 'balance' that equates to 100%.
If you change any one of them, one or both of the other two values also have to change to compensate, to keep things 100%.
Its for this reason that increasing the dpi results in a smaller output size, and increasing the output size decreases the dpi.
What you change depends on your output criteria, if you HAVE to print @300dpi then you set the dpi to 300 and adjust the other two.
If you HAVE to have a 6" x 4" output size then set the doc size to 6" and 4" and adjust the other two.
If you don't want to up-scale or down-scale, and btw you don't, then leave the px dims and adjust the other two.
If you've ever done photography its very much the same balancing act as Aperture, Shutter speed and ISO for the correct exposure.....changing any one means compensating with one or both of the other two.
I hope that explains those dialogs a little better.
Try not to up or down scale, (Leave the px dims alone and turn OFF Resample Image), and adjust the other values to fit your requirements.
Regards.
MrTom.
