What is bracket?
What does bracket do?
What is an HDR image?
How can I create an HDR image?
What is Tonemapping?
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What is bracket?

bracket is a high-dynamic-range (HDR) photo manager. It understands the most commonly used HDR file formats such as RGBE, EXR, and floating point TIFF (including LogLuv encoding). It also dabbles as a low-dynamic-range (LDR) photo manager by giving support to standard JPEG and TIFF image formats.

bracket works on all major platforms (Windows, Mac, and Linux) as it is designed using FLTK - an excellent cross platform user interface library.

What does bracket do?

bracket can be used to create, tonemap, and display HDR images. It allows conversion between different image formats, and provides support for basic image editing tasks such as rotation, cropping, flipping and resizing. It supports batch operations to easily perform these tasks on a large number of images.

bracket supports basic file management operations such as creating and deleting directories; copying, pasting, deleting, and renaming images. This allows to perform commonly used photo organization jobs such as transferring images from a digital camera to the hard-disk, or moving files around without quitting the application.

It can also be used to view extensive EXIF meta-data information, image statistics, and pixel values.

What is an HDR image?

Simply put, an HDR image is an image whose pixel values exceed the typical 8-bit per color channel range, and therefore cannot be directly stored in conventional image formats. Furthermore, the pixels of an HDR image are usually represented in floating-points as opposed to integers for improved accuracy.

The benefit of working with HDR images is the improved fidelity throughout an entire image processing pipeline. More specifically, starting with the initial capture of an HDR image, and including later processing, the pixel values are not clamped or quantized to a limited range. This allows capturing an almost lossless representation of an original scene and preserving it throughout the entire image processing pipeline up until the display stage. At that point, the dynamic range can be reduced to the display device's capabilities via an operation called tonemapping.

How can I create an HDR image?

HDR images can be directly captured with specialized cameras; but currently these devices are expensive and not widely available. The second best alternative is to use typical digital or SLR cameras to capture a bracketed exposure sequence and combine them into an HDR image. Since each exposure will be properly exposed for a different part of the captured scene, their combination will accurately represent the entire scene. This operation can be easily performed using "Create HDR..." option in bracket.

What is Tonemapping?

Tonemapping is the process of reducing the dynamic range of an HDR image while trying to preserve some of the important image attributes such as perceived contrast, brightness, color appearance, etc. Tonemapping, by definition, is a lossy operation but it is necessary to prepare an HDR image for display on a low dynamic range display device. Because most of the current display devices are low dynamic range, tonemapping is an indispensible component of an HDR image processing pipeline. As HDR display devices become more widely used, the nature or the extent of the tonemapping is likely to change.

bracket gives the user two tonemapping options namely the Photographic Tonemapping Operator and the "Photoreceptor" Tonemapping Operator. The former is among the most popular tonemapping operators currently in use, as it automatically preserves the general photographic look of an HDR image. The "photoreceptor" operator, on the other hand, allows the user to change parameters such as saturation, lightness, contrast, and gamma to further customize tonemapping results. The implementation of both operators are kindly provided by Erik Reinhard. For more information, check out the following references:

Erik Reinhard, Michael Stark, Peter Shirley and Jim Ferwerda. "Photographic Tone Reproduction for Digital Images", ACM Transactions on Graphics, 2002.

Erik Reinhard and Kate Devlin. "Dynamic Range Reduction Inspired by Photoreceptor Physiology" ", IEEE Transactions on Visualization and Computer Graphics, 2004.

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