Resizing Photos in iPhoto for the Web
Sometimes when I want to upload photos to a site there are size restrictions. The photos my digital camera takes are enormous in file size, so I need to trim them down to put them online. If I resize the dimensions of the image to be smaller, then the filesize will decrease.
Image files a digital camera takes can have big dimensions. My 7.0 Megapixel camera takes pictures 3072×2304 @ 72 dpi. What does this mean? The image’s dimension is 3072 pixels wide and 2304 pixels high. The image’s resolution is 72 dots per inch. 72 dpi is the web standard for image resolution. Any higher resolution significantly increases file size. If I pack 300 dpi into the same image, there are many more pixels, making the changes in color more detailed. 300 dpi is good for printing an image, but that’s a whole other discussion.
Since most digital cameras’ resolution is 72 dpi, all I really have to worry about are the dimensions when resizing a picture to give it a smaller filesize.
To check an images information in iPhoto, select an image in the library and hit Apple+I.
To resize a photo in iPhoto 6 I must first select the file or files I want to resize. I can resize more than one image by cherry picking images in the library by holding down Apple as I select images. Or if the images are in a list, click the first image, hold down Shift and select the last image.
Once the images are selected:
In iPhoto 6, go to the top menu and select File: Export.
In older versions of iPhoto, go to the top menu and select Share: Export.
A settings window appears. This is where we will change the filesize of the image to be more appropriate for the web.
Different websites have different guidelines for the maximum filesize an image can be. A good and standard dimension to make a photo for the web is 1024×768. This gives the ability for others to even use the images as a decent wallpaper. Images exported as a 1024 x 768 JPEG will most likely be around 500 - 600 kilobytes in filesize. This is still under a megabyte. I noticed MySpace has a 600 megabyte rescriction for photos. If the filesize needs to be smaller, make the image 800 x 600.
Select JPG from the format selector.
Enter 1024 into the width dialog. iPhoto automatically knows the height should be 768.
Make sure use file extension is checked.
Check Use filename if I want the image’s filename to be the same. In the next dialog you can even give the image a different filename. Or if you want to rename the images based on the album they are in, select Use album name.
Click Export.
Choose the folder where I want to export the picture(s).
In this box, make sure .jpg is at the end of the filename.
Hit OK.
What did you learn in this post?
Or did it leave you with further questions?
Comment here to Ask Steve Blue!
Written by Steve Blue
steveblue@iuseapple.com
AJ
that was very helpful. I was trying to figure this out for a bit. The only way I could find is to send it as an email, it then let me resize it then.
Your method is obviously better this I can just resize it and do what I want with it.
Oct 16th, 2006 11:15 am
Annemarie
But how do I change an image from 300 dpi to 72 dpi in iPhoto? I have a bunch of images set at 300 dpi for printing but cannot see where i can change them to 72 dpi in iPhoto for uploading to the web.
Thanks
Nov 5th, 2006 7:37 pm
steveblue
If I select File Export and go to the web page tab, select the proper dimensions, and select Export. This process will make a website, with images that are 72 dpi.
Nov 5th, 2006 10:38 pm
kat
Okay, how about the reverse … what if I have a large image in 72 dpi. A site is requiring a smaller size (get how to do that now–thanks!) but at 300 dpi. Any ideas?
Jan 12th, 2008 2:24 pm
steveblue
Kat,
Photoshop is more appropriate for this kind of Image Handling. If you change the resolution to 300dpi in Photoshop, it will automatically calculate the Image Size. You must sacrifice the image dimensions and make it a smaller image to get a higher DPI. It works on the same ratio. So if you are going from 72dpi to 300dpi, this is a 4.16X magnification in resolution. The image size would then need to be divided by this same amount. So, if the width of the image was 3,692 pixels, The new width would become 887.5 pixels. This will scale the image without distortion.
To scale from 72dpi to 300dpi without sacrificing image size uses a process called Vectorization. You must actually create new pixels where there were none before. This is a complex process. I do not know much about this…
Jan 13th, 2008 9:24 am
Gudrun
thank you, thank you! This simple, straightforward tip has just saved me a great deal of time. All I needed to do was make some images smaller to post in an ad on Craigslist and I kept finding sites that wanted to go into all the math and science behind image size. Thank you for being direct and to the point!
Out of curiosity, do you know anything about photographing food? That is my next challenge….
Apr 11th, 2008 11:19 am
Craig
Sorry, but you have repeated a fundamental myth about web graphics…that they need to be 72dpi. 72dpi comes from the first days of the Mac computer when the screen was 72dpi and so to get a one to one correspondence from the screen to the printed page this became a kind of standard for desktop publishing. Now days most screens are around 100dpi. The file size of an image is determined only by its pixel dimensions and amount of compression. A 1024X768 image at 300 dpi is exactly the same size as a 1024X768 image at 72 dpi. Dpi is only relevant when printing an image. The 300 dpi image will print much smaller than the 72 dpi one. I usually have to show people in Photoshop that this is true because the 72dpi mantra has been so often repeated. If you only change the dpi you will notice that the pixel dimensions and file size increases. If you then change the pixel dimensions back to what they were you will see that the file size returns to the same value. One benefit of keeping an image at a high dpi is that if someone where to download it and try to print it it would probably be so small they wouldn’t be able to use it.
Jun 3rd, 2008 1:43 pm