Academic journal article Rock Art Research

Free Image-Enhancement Apps for iPad (LabStretch) and iPhone (LabStretch2)

Academic journal article Rock Art Research

Free Image-Enhancement Apps for iPad (LabStretch) and iPhone (LabStretch2)

Article excerpt

Tools for image enhancement are widely available for computers. These include Photoshop (Mark and Billo 2002) and DStretch (Harmon 2008). These techniques are fundamentally based upon histogramstretching in various colour spaces. We recognised the need for image-enhancement in the field, with devices commonly available. As a step in this direction, we have developed iOS apps to do stretching in the Lab colour space. Lab separates the pixel luminosity from the colour information, which is encoded in two orthogonal colour channels. These are then separately stretched by adjusting sliders. Figure 1 is a screenshot of the iPad app showing the sliders and the before/ after images. Figure 2 shows the process for using LabStretch.

The apps are available, for free, from Apple iTunes. Links for download, as well as instructions, are available at http://www.rupestrian.com/labstretch.html.

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Instructions

1. Image acquisition: use either Capture Image, which takes a photo with the iPad/iPhone from within the app (this will not allow you to save the original image, but is useful for quick look to see basic initial spread enhancement), or Import Image, which selects a photo from the camera roll. If you know in advance that you will want to keep the image, use the camera app and import the image from the camera roll

2. …

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