tev — The EXR Viewer

A high dynamic range (HDR) image comparison tool for graphics people. tev allows viewing images through various tonemapping operators and inspecting the values of individual pixels. Often, it is important to find exact differences between pairs of images. For this purpose, tev allows rapidly switching between opened images and visualizing various error metrics (L1, L2, and relative versions thereof). To avoid clutter, opened images and their layers can be filtered by keywords.

New: tev can display true HDR on Apple extended dynamic range (EDR) and 10-bit displays.

While the predominantly supported file format is OpenEXR certain other types of images can also be loaded. The following file formats are currently supported:

EXR (via OpenEXR)
PFM (compatible with Netbpm)
DDS (via DirectXTex; Windows only. Shoutout to Craig Kolb for adding support!)
- Supports BC1-BC7 compressed formats.
- Low-dynamic-range (LDR) images are "promoted" to HDR through the reverse sRGB transformation.
HDR, BMP, GIF, JPEG, PIC, PNG, PNM, PSD, TGA (via stb_image)
- stb_image only supports subsets of each of the aforementioned file formats.
- Low-dynamic-range (LDR) images are "promoted" to HDR through the reverse sRGB transformation.

Screenshot

A false-color comparison of two multi-layer OpenEXR images of a beach ball. Image courtesy of openexr-images.

Usage

Graphical User Interface

Images can be opened via a file dialog or by dragging them into tev. They can be reloaded, closed, or filtered at any time, so don't worry about opening more images than exactly needed.

Select an image by left-clicking it, and optionally select a reference image to compare the current selection to by right-clicking. For convenience, the current selection can be moved with the Up/Down or the 1-9 keys. For a comprehensive list of keyboard shortcuts click the little "?" icon at the top (or press "h").

If the interface seems overwhelming, you can hover any controls to view an explanatory tooltip.

Command Line

tev takes images as positional command-line arguments:

$ tev foo.exr bar.exr

By default, all layers and channels are loaded, but individual layers or channels can also be specified. In the following example, the depth layer of foo.exr and the r, g, and b channels of foo.exr and bar.exr are loaded.

$ tev :depth foo.exr :r,g,b foo.exr bar.exr

Other command-line arguments exist (e.g. for starting tev with a pre-set exposure value). For a list of all arguments simply invoke

$ tev -h

Over the Network

tev can also be controlled remotely over the network using a simple TCP-based protocol.

The --host argument specifies the IP and port tev is listening to. By default, tev only accepts connections from localhost (127.0.0.1:14158), which is useful, for example, as frontend for a supported renderer like pbrt version 4.

The following operations exist:

Operation	Function
`OpenImage`	Opens an image from a specified path on the machine tev is running on.
`CreateImage`	Creates a blank image with a specified name, size, and set of channels.
`UpdateImage`	Updates the pixels in a rectangular region.
`CloseImage`	Closes a specified image.
`ReloadImage`	Reloads an image from a specified path on the machine tev is running on.

tev's network protocol is already implemented in the following languages:

Python by Tomáš Iser
Rust by Karel Peeters

If using these implementations is not an option, it's easy to write your own one. Each packet has the simple form

[uint32_t total_length_in_bytes][byte operation_type][byte[] operation_specific_payload]

where integers are encoded in little endian.

There are helper functions in Ipc.cpp (IpcPacket::set*) that show exactly how each packet has to be assembled. These functions do not rely on external dependencies, so it is recommended to copy and paste them into your project for interfacing with tev.

Obtaining tev

macOS / Windows

Pre-built binaries for Windows (32-bit and 64-bit) and macOS (64-bit) are available on the releases page.

Linux

Archlinux: available on the Arch User Repository

Building tev

All that is required for building tev is a C++17-compatible compiler. Begin by cloning this repository and all its submodules using the following command:

$ git clone --recursive https://github.com/Tom94/tev

If you accidentally omitted the --recursive flag when cloning this repository you can initialize the submodules like so:

$ git submodule update --init --recursive

tev uses CMake as its build system. The following sections detail how it should be used on various operating systems.

macOS / Linux

On macOS and most Linux distributions CMake can be obtained via a package manager (Homebrew on macOS, apt on Ubuntu/Debian, etc.). Most Linux distributions additionally require xorg, gl, and zlib development packages and zenity. On Ubuntu/Debian simply call

$ apt-get install cmake xorg-dev libglu1-mesa-dev zlib1g-dev zenity

Once all dependencies are installed, create a new directory to contain build artifacts, enter it, and then invoke CMake with the root tev folder as argument as shown in the following example:

$ mkdir build
$ cd build
$ cmake ..

Afterwards, tev can be built and installed via

$ make -j
$ make install

Windows

On Windows, install CMake, open the included GUI application, and point it to the root directory of tev. CMake will then generate Visual Studio project files for compiling tev. Make sure you select at least Visual Studio 2017 or higher!

License

tev is available under the BSD 3-clause license, which you can find in the LICENSE.md file. TL;DR you can do almost whatever you want as long as you include the original copyright and license notice in any copy of the software and the source code.

mcrescas / tev