iDownsize is a fairly new photo app that “allows the compression of selected photos or entire albums.” This can save valuable storage space on your iPhone or iPad, but the App Store description is a little misleading. There is a difference between “compression,” a word which iDownsize uses often, and “downsampling.” iDownsize lands on the wrong side of that distinction. Know what you’re getting into and use this app with caution.

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When I first saw this app, I thought iDownsize simply resaved images at the same size but with greater compression. I initially thought that it simply resaved images with Maximum Quality JPEG compression (10 or 11 in Photoshop) with High Quality compression (6 or so) in order to save space. The visible difference between the two settings would be visibly imperceptible in most cases. That would actually be a cool utility to have.

What iDownsize does is more destructive than that. iDownsize resamples images, making the image itself smaller in order to reduce file size. The app defaults to 50% size — that’s destroying half of your pixels. Image size reduction is user adjustable.

The app is fairly simple to use. Choose any photos from your device to downsize, including those from the Camera Roll, Photo Stream, and photo albums. Select the compression level. Preview onscreen. Name a destination album and start downsizing. You can add new photos to an existing iDownsize-created album by simply naming the new destination album the same name. This won’t work on iPhoto-created albums.

Also, you can’t delete or edit iPhoto-created albums on your iPhone. Once you save an iDownsized version to your phone, you’ll have to go back to iPhoto and unsync the photo album, letting the duplicate, low-res album to remain on your iPhone. Confusing.

Fortunately, the app does not delete any photos on its own. It saves copies and expects you to manually delete them. If that’s by design and not because Apple doesn’t allow developers to mess with the contents of the iPhone’s Camera Roll and photo albums, it was a very smart choice.

The smaller, downsized images not only save to their new photo albums on my iPhone, they save back into the Camera Roll. Not only does this duplication negate any filesize savings, this is also confusing and very dangerous. Depending on the source of your image, it’s possible to delete your full-resolution copy of the image before you’ve had a chance to save it.

Once pixels are deleted from an image, they cannot be replaced exactly, even with upsampling.

iDownsize only reduces the file size of images on your iPhone. It will create a new copy of the file and won’t effect the full resolution image in your iPhoto library. But, having multiple copies of a photo is confusing. It’s also dangerous when one of those copies is low-resolution.

Why would you want to downsize? The app’s description says to save up to 2 gigabytes of space on your iPhone. If you have one of the lower capacity iPhones, space is at a premium. More smaller sized files will fit on your device. The iPhone already uses some form of this to save space — it already downsamples images from your iPhoto photo albums back to your device at 3 MP or 2056×1536. To save space on your iPhone, Apple used to save images in Photo Albums back to the device at about 1 megapixel — less, actually. They looked fine onscreen, but lost much of the detail when you tried to zoom in to view closer.

Other reasons to downsize images also include saving bandwidth usage on your data package. Smaller photos use less data to upload an email. Many apps including Apple Mail already give you this ability — some without a choice.

In short, there is almost never a good reason for iPhoneographers to downsize images on their iPhone.

The concept of iDownsize is good — to reduce image size and optimize space on your iPhone. Overall, iDownsize is one of the more well-thought out, slicker downsizing apps. If image resolution is not an important factor to you, if you’re only showing and sharing images online or on your device, then this could be a handy utility for you to consider for what it does, which is reducing the image size of a large number of photos on your device quickly.

But, it has some issues, including misleading terminology, version duplication, and adding low res images back to the Camera Roll and Photostream. Know what your getting into when you use this app.

A better, safer solution is to manage the photo albums on your device, manage and delete photo apps you never use, clean out unwanted images from your Hipstamatic library (those images have already been saved to your Camera Roll and are taking up twice as much space), clean out your music library of songs you never listen to any more.

iDownsize is $0.99. It’s a Universal app that will run great on iPhone or iPad. Requirements: Compatible with iPhone 3GS, iPhone 4, iPhone 4S, iPod touch (3rd generation), iPod touch (4th generation) and iPad.Requires iOS 5.0 or later.

iDownsize - Michael Tüllmann