Re-sizing for printing

[Alejoviade]

I'm somewhat confused regarding the re-sizing of the pictures for print output. I have several questions so I will ennumerate:

FYI I use a Canon 30D and take pictures in RAW (with the default 72 ppi)

After making the necessary adjustments I feel I need on a specific photo then a save it as Jpg for future printing but I get somewhat confused (although I have read many books) when I need to resize it.

The pics are 72 ppi and very very large by default, so I usually change the ppi to about 300 to make it "good" for printing. I uncheck the Resample Image and type in the 300ppi but although now I get the resolution I want the picture size changes considerably.

Question 1: How do I make the picture 300ppi but let's say keep it at a size of 12 x 8 ?

Question 2: Although when I make changes I see the file size changing (for example from 7MB to 23MB when I look at the details of such file (windows explorer) it still shows as 7MB, What happened to the 23MB file ?

[Damo77]

Hi Alex,

It's important to understand that resolution is completely irrelevant until the output stage. An image contains a certain number of pixels, as dictated by the sensor in your camera (I can't remember the capacity of your 30D off the top of my head). Changing the resolution has no effect on file size.

Therefore, when you say:

I uncheck the Resample Image and type in the 300ppi but although now I get the resolution I want the picture size changes considerably.

you need to be aware that the file size hasn't changed at all - you've still got exactly the same number of pixels as before.

So ...

If you want an 8x12 image at 300ppi, you'll need 2400x3600 pixels (8*300 by 12*300). If your camera doesn't shoot an image that big in the first place (and it should), Photoshop needs to do some interpolation to make it that big.

The best way to get the image size you want without doing the mathematics, is to choose the crop tool and enter 8, 12 & 300 in the options bar. Then crop away merrily.

Question 2: Although when I make changes I see the file size changing (for example from 7MB to 23MB when I look at the details of such file (windows explorer) it still shows as 7MB, What happened to the 23MB file ?

I hope I'm answering your question correctly. If your original file is a JPEG, then it's compressed, of course. When you open it in Photoshop, it decompresses so you can edit it. Then if you save it as a JPEG again, it'll go down to 7MB again (or thereabouts). Much has been written in this forum about the advantages vs problems of JPEG saves.

[Alejoviade]

Thanks so mucho for the response and clarification to this issue. I guess I will just leave the photos in their original state and only work on their resolution when getting to the printing stage. Using the crop tool the way you indicated will ease the workflow as well, appreciate your help !!!

Cheers !!!

Alex