By Graham K. Rogers

As a student in the UK (many years ago of course) I visited establishments where people would throw their bodies about to music. A feature of many of these were mauve colored lights (bulbs or tubes) that when on, would make certain colours glow, especially white. These ultra-violet lights are also called "Black Lights" and while we see the visible light as mauve, the ultraviolet light itself is invisible: we just see the effects.

A free app for iOS devices, Blacklight, takes the idea of these different light effects and allows users to take photographs, or use images already in a library, and apply similar effects quite simply and quickly. I installed this on my iPhone 5s.

An opening screen is displayed for less than a second and shows a black panel with a nicely drawn image of a lightbulb in violet. The app opens to a single panel which is simply designed with a small number of controls under a panel for image display.

At the very bottom of this screen are three buttons: Library, Camera and Save. Immediately above these buttons are three sliders for Red, Green and Blue levels. There is one more slider, marked "Intensity", while to the right of this is a button marked, "Toggle Blacklight". When pressed, this displays the original image (or can then be pressed again to turn Backlight on once more).

The RGB sliders increase the level of the specific color as the slider is moved to the right, while the Intensity slider increases the amount of light in the image as it is moved right.

With only 4 main controls, adjusting an image is quick and easy; and if the end result is not completely satisfactory, it is simple to do it again. Once the image is adjusted, pressing the Save button adds it to the Photo Library.

The images I saved were synchronised with Aperture, using PhotoStream where I found them to be 1600 x 1200 (1.9 MP) and between 700 and 750 KB file size. One image that I had cropped before was 1600 x 1060 (1.7 MP) and 693 KB.

I exported one of the normal size images as a 16-bit TIFF file. The resultant image was just over 22" x 16.5" (72 dpi) with a file size of 11.5 MB: respectable enough.

The app has not been optimised for the iPad and I found that it opened in the usual x1 or x2 screens. It is identical to the app on the iPhone and the output is also about the same at 1067 x 1600 (a cropped portrait mode image of 1.7 MP) at 741 KB.

On one level, Blacklight is just an app for producing basic effects from camera input or using images already in the library. A plus point is the simplicity of the app: there are no unnecessary frills, but there is considerable flexibility when adjusting images.

As a free app, there is no real decision to make here and Blacklight stays in my collection.

Graham K. Rogers teaches at the Faculty of Engineering, Mahidol University in Thailand where he is also Assistant Dean. 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.