By Graham K. Rogers

When using apps for photography on the iPhone and the iPad, I am usually more interested in adding to the image or changing the look of the output by way of filters or editing (e.g. contrast, saturation). In some cases however, removing information from an image is useful, especially if the image is to be used in a specific web context, in a text page, or as a layer in another image file.

For a couple of weeks, I have been using a farily simple app called Background Eraser for iPhone. It was priced at $0.99. As the name suggests, it removes parts of a picture, such as might be done with the erase tool in Graphic Converter on a Mac (or with the equivalent in Adobe Photoshop).

Eraser

This ? reveals a useful screen with three buttons. The top one (in red) is marked "Report a Problem, Ask" which switches to a part-completed email for the user to enter any query that the developer would be able to answer. The second button is for a Tutorial. This opens Safari and links to the Support pages of the developer HandyCloset. The final, Tell a Friend button allows information to be posted using links to Facebook, Twitter, or via email, or message. The final button here is marked Copy Link.

Pressing Load Image opens a panel with one button, marked Load Image (perhaps redundant) that opens the Photo Album on the iPhone. Selecting an image opens it in the Eraser panel and the user has the opportunity to crop in two ways: there is a simple grid pattern superimposed and arrows at the side show where these can be moved inwards to reduce the image area; at the bottom of the screen are a number of preset sizes (e.g. 1:1, 9:16). The presets and grid may be used in conjunction with each other.

When the size has been adjusted (or not, if the full image is to be used), the Done button is pressed and the image is displayed onscreen. A user should now press button 2 at the top of the screen, Eraser.

Editing

• At top left is a white cross in a red button for cancelling the edit;
• Auto allows the erase effect to be applied by area selection
• Color erases a specific color section in a selected area
• Manual affects only a specific small area (as opposed to larger areas erased with Auto)
• Repair displays areas that are marked for erasing and allows adjustments to be made
• Zoom provides the ability to zoom the image (or make control areas smaller) so that minute adjustments can be made.

The trick is in the two windows that are provided for image editing. The main window shows the full image (unless zoomed with the "pinch") while a smaller panel at the top shows the exact area of the image that is being edited. Cross-hairs indicate the exact point of the edit, and this matches a larger red circle in the main panel. A control circle (on which the user places the finger) is just below. Distance between the two is adjusted by way of the Offset slider: from 0 when the control circle is at center of the editing one, up to 200 when the two are about 1 centimeter apart (on the iPhone).

As I tried editing the image, I occasionally (often) erased more than I wanted, so the Undo button (and Redo) at the bottom were most useful, as were the Zoom and Repair functions. A color threshold slider at the bottom also helped in adjustments to the amount of an image that was erased. In Manual mode this changed to allow the radius of the eraser control to be adjusted.

When the user is satisfied with the result, there is a Done button, which (again redundant) brings up a panel with a Done button on it. The user is returned to the main screen where the image is displayed.

The final button is 3. Save. A panel is opened with two options: a red button with "Save (PNG, Transparent)" on it and a white button with "Save (JPEG, White). Above the buttons is a warning concerning the way the Photo Album displays transparent images (with a black background). It is suggested that to check, the image be reloaded. I saved one of each. The PNG image was indeed black, and was the same when synced with a Mac using Photostream.

I exported the image and used it in a web page I wrote to test this. Indeed it was transparent and the erased sections did not block the red background I had used for the purpose.

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Graham K. Rogers teaches at the Faculty of Engineering, Mahidol University in Thailand. He wrote in the Bangkok Post, Database supplement on IT subjects. For the last seven years of Database he wrote a column on Apple and Macs.