Why Should I "Throw Pixels Away?"

[George Tyndall]

1. With the settings I've chosen, my camera makes images that are 2288x1520 pixels (3:2 ratio). The associated document size, according to Photoshop's Image Resize dialog is 31.778x21.111 inches at a resolution of 72 pixels/per inch.

2. According to Epson, the quality of my prints on US letter-size paper will deteriorate if the output is less than about 220 ppi.

3. So what I've been doing, for years, is to leave Resample Image unchecked and type in 10.5 inches for the width of my output. With Constrain Proportions also checked, the other dimensions come out to about 7 inches and the new resolution about 218ppi. I've been VERY happy with this output as it looks wonderful in a frame with the same 3:2 aspect ratio.

But in the course on Photoshop that I am taking, the instruction is as follows:

Now, what if you decided at this point that you wanted another copy of this
05:51 image even smaller, one that might fit in your wallet. You know that you have
05:55 to leave the resolution at around 300 pixels per inch, because you are going to
05:59 print the image. But, you'd like the dimensions to be smaller, how do you do
06:03 that? You go back to the Image menu and again you choose Resize Image Size.
06:09 This time in the Image Size dialog box, I'm going to go down to Resample Image
06:14 and make sure that it's checked.
06:16 Now take note again of the width and height in pixels. 1800 pixels across by
06:21 1200 down, but if I come down to the Document Size area, and change the width
06:26 and height, watch what happens. I'm going to type 3 inches in the Width field
06:30 and that automatically changes the Height field to be proportional. If you look
06:35 back at the pixel dimensions, instead of 1800 pixels of width, we now have only
06:40 900, and instead of 1200 pixels of height, we now have only 600. Again, that's
06:45 because I've changed this formula down here.
06:47 The Resolution has stayed at 300, but I changed the Width to 3 and if you
06:52 divide 900 pixels by 3, you get a resolution of 300. So basically, what I've
06:58 done here is to throw away some pixels in order to make a smaller copy of this
07:01 file and that's okay as long as I'm working on a copy.
07:05 One more thing, when I resize an image like this to make it smaller, the best
07:09 thing to do is to come to the field labeled Bicubic and click there and make
07:14 another choice, Bicubic Sharper. This tells Elements what formula to use when
07:19 it throws away pixels to make this image smaller and when you are downsizing as
07:23 I just did, the Bicubic Sharper formula works better and gives you a better
07:27 result than the default Bicubic formula. So I'm going to choose that one.

My question is, Why would I want to "throw away pixels" by checking the Resample Image box when my goal is to get the largest possible image possible, in inches, without dropping below 220 ppi? Don't I want to conserve those 2288x1520 pixels, rather than throw some of them away?

[Bob]

My question is, Why would I want to "throw away pixels" by checking the Resample Image box when my goal is to get the largest possible image possible, in inches, without dropping below 220 ppi? Don't I want to conserve those 2288x1520 pixels, rather than throw some of them away?

In my opinion, if you can get to that 220 ppi level without resampling you wouldn't resample. Sometimes you have to resample like when you are preparing a photo for use on a web site or in a video and ppi has no meaning as the size is a function of absolute pixel dimensions. But, for prints, you usually scale using the ppi without resampling. Scaling sends all the pixels to the printer and the printer driver adjusts the spacing and size of the dots. The downside is that because every pixel will need to be dithered to physically print the correct mix of ink dots to reproduce the pixel color, it will take longer to process and print the image. For inkjet printers, you won't benefit from excessively large ppi values. Depending on the printer, your optimum is probabaly around 300 ppi and could possibly go up to around 360 ppi. Beyond that, you're just lengthening your print time unnecessarily. In those cases, you may want to consider resampling to a smaller image.

If you do decide to resample, definitely work on a copy. You don't want to resample your original.