Here is a quick run through on Photoshop Elements 2.
Photoshop should be similar.
Open your 640 x 480 photo.
Click Image, Resize, Image Size
That brings up the Image Size window.
If the check box "Resample Image" is checked, uncheck it.
You should see 640 and 480 greyed out at the top.
At the bottom, you should see:
Width 8.889 Inches
Height 6.667 Inches
Resolution 72 pixels/inch
Change the Resolution to 300 and you will see:
Width changed to 2.133 inches
Height changes to 1.6 inches
If you printed the photo now, it would print at a size of 2.133 x 1.6
Now - checkmark "Resample Image"
Note: the greyed out area at the top of the window has turned white.
Now change the Width to 6 inches.
Notice all the changes.
Height has changed to 4.5
The pixels at the top of the window have changed to
1800 x 1350
Click OK
You now have a 1800 x 1350 image.
Save it with a new name to keep from overwriting your original file.
You now have an image that will print at 6 x 4.5 inches.
Print it and see how it looks.
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Now that you know how, I can point out a few problems.
1.
Your final file size will not exactly fit on 6 x 4 inch paper. It is too tall.
Your final size file, when printed on 6 x 4 inch paper will be automatically cropped to fit on the paper. Usually .25 inch is cropped from each the top and bottom.
You should have cropped the photo first before printing it. Then you control where the crop happens.
2.
You have upsized a photo from 640x480 to 1800x1350.
Where did those extra pixels come from?
Photoshop made them up by interpolation.
When you upsize a photo, it degrades the photo to some degree.
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Can anyone tell me how to actually "resample to 300dpi". I need an image to be 300dpi and 4x6 size. In all the software I have it only shows pixels. I know that pixels and dpi are different, but in this case is it maybe the pixels I want to change? I am using Photoshop. The image size is currently 640x48 pixels per inch and resolution is 72 pixes per inch.
I appreciate any help I can get!

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