I am attempting to change the dpi of several images for my publisher, from 72 to 300 dpi. The Inspector box shows that I've made the change, until I go to save the change, and it reverts back to the 72 dpi. What am I doing wrong?
MacBook Pro, Mac OS X (10.7.5)
Not understanding DPI is the issue
And this forum is only about iPhoto for the Mac not about Preview
DPI is Dots Per Inch is a mathematical calculation rather than a setting - to know the DPI you first must know the pixel dimensions of the image - get this from the Info pane in iPhoto - then you need inches which you get from the person who is going to print the image - digital images have no inches, only pixels - physical images (computer displays are usually 72 DPI displays) do have DPI but you calculate it rather than set it
So if you want to print an image at 8" x 10" and 300 DPI then the digital image image must be 2400 x 3000 pixels or larger - see http://www.rideau-info.com/photos/mythdpi.html
That being said there is a meaningless DPI field in the EXIF data - while it makes no difference at all you can set a clue in that meaningless field in PhotoShop Elements and maybe other programs - you can not in iPhoto
LN
Here's an illustration to what Larry is referring to:
This image, 3200 x 2000 pixels will produce a 72 dpi print of 44.4 inches x 27.8 inches. However, at 300 dpi the print size shrinks to 10.7 x 6.7 inches. So you need to know what is the largest size that that image will be printed to and provide that number of pixels or more. It won't hurt to have more pixels than the print size at 300 dip calls for.
Thank you both.
None of your responses addressed the problem, which I take full responsibility for not being clear about.
In Preview, I am able to change the dpi of my photos from 72 to 300, which is what the publisher is requesting, but unless I click on the "Resample Image" button (which I didn't think I was supposed to do), I am unable to Save the changes, the dpi reverts automatically to the original 72. If, however, I am willing to keep the "Resample Image" button clicked, then the 300 dpi is saved along with a much larger overall pixel count.
I am going to have to let the publisher know that I can supply one, or the other. Interestingly, I have tried printing out several of the modified (300 dpi) images, and the "output" (in my case, 4" x 6" images) remained the same.
Carol
They did - read them again
It is very clear and simple - DPI is NOT a setting - it is a calculation - you divide dots (pixels) by inches and you get DPI
Changing a meaningless number in the EXIF data does not change the DPI any more that taking your bank statement and crossing out the balance and writing a larger balance in gives you more money - it is a meaningless change - DPI is only the answer to a calculation -- it can not be changed by putting a different number anywhere Re-read the answer above and read the link provided - emphasis addd
Not understanding DPI is the issue
And this forum is only about iPhoto for the Mac not about Preview
DPI is Dots Per Inch is a mathematical calculation rather than a setting - to know the DPI you first must know the pixel dimensions of the image - get this from the Info pane in iPhoto - then you need inches which you get from the person who is going to print the image - digital images have no inches, only pixels - physical images (computer displays are usually 72 DPI displays) do have DPI but you calculate it rather than set it
So if you want to print an image at 8" x 10" and 300 DPI then the digital image image must be 2400 x 3000 pixels or larger - see http://www.rideau-info.com/photos/mythdpi.html
That being said there is a meaningless DPI field in the EXIF data - while it makes no difference at all you can set a value in that meaningless field in PhotoShop Elements and maybe other programs - you can not in iPhoto
LN
Thank you for your help. I will share these insights with my publisher.
Best regards,
Carol Mossa
If your publisher can't get their head around this, then you may need to use a heavier duty picture editor like Photoshop Elements that will let you go in and change just the setting for the dpi, though as pointed out, this has absolutely no effect on the image, except how it is displayed.
Just spoke with the publisher. It's all good. Your explanations here really helped me to speak their language. I can't thank you all enough for simplifying the whole discussion. I can submit the images just as they are (72 dpi), but you all probably already assumed that's what would happen! LOL
Carol Mossa
www.earthsschooloflove.com
The point here IS THAT SOMETHING HAS CHANGED IN PREVIEW.
Once upon a time you could click in the DPI box and change the number from 72 to 300 and the photo would resample and save. IT NO LONGER DOES THIS.
Can anyone explain WHY it no longer does this???
Why are you shouting at people? Why are you asking on the iPhoto forum? Why does it matter as it's meaningless anyway.
Can't save modified dpi in Preview.
