EXR header values¶
This module represents EXR headers as regular Python dictionaries.Each header entries have a name - a string - and a valuethat may be one of several types, defined by the OpenEXR standard.
The Python module translates these types to Python types when reading OpenEXR headers,and does the reverse translation when writing headers.
Enable snaps on CentOS and install OpenEXR Viewer. Snaps are applications packaged with all their dependencies to run on all popular Linux distributions from a single build. They update automatically and roll back gracefully. Snaps are discoverable and installable from the Snap Store, an app store with an audience of millions. Redistribution and use in source and binary forms, with or without modification, are permitted provided that the following conditions are met.
The module Imath provides many of the classes for attribute types.
Values in the dictionary may be:
string
float
View OpenEXR, Radiance RGBE, and DirectDraw Surface images. View JPEG XR HDR screenshots taken by Windows 10 or Xbox One. View high bit depth and wide color gamut images like JPEG with ICC profile and TIFF. View images at their full native quality on a capable HDR10 or WCG display. On SDR displays, view images at the best available. RAW Viewer 2.2.1 Update Fixed a bug that prevented RAW files from previewing correctly when using the NVIDIA GeForce 340.52 drivers for Windows Improved DPX/OpenEXR export performance. Openexr-viewers viewer for images in the OpenEXR format. 2020-04-10 openexr-viewers 2.3.0-1 MIGRATED to testing (Debian testing watch).
int
list of strings
New in version 1.2.
This attribute type is used in multiView images, as described in http://www.openexr.com/MultiViewOpenEXR.pdf
dict
A dict represents the image’s channels. In the dict, the keys are the channel names, and the values are of class Imath.Channel:
A preview image, specified by height, width, and a string of length 4*width*height. The pixels are in RGBA order:
or to use a PIL image as an EXR preview:
Imath.Chromaticities
Specifies (x, y) chromaticities for red, green, blue and white components:
Revealing More Detail in OpenEXR Images
This section gives a short tutorial on using the exrdisplay program, which is included with the OpenEXR software distribution.
You can reveal more detail in OpenEXR images by changing the exposure using the Exposure slider. This operation is analogous to changing the exposure of a piece of film, lightening or darkening the image to reveal more detail at the high or low end.
With exrdisplay, however, changing the exposure does not affect image data itself, it simply changes the way that the original 16-bit floating-point pixel values in the image are converted to 8-bit integer data in the frame buffer. We call the original 16-bit FP pixels the 'raw' image data, and the converted 8-bit pixels the 'cooked' image data. When you change the exposure, you are 're-cooking' the data.
For example, in the following image you can see the light areas (fog) very clearly but in the dark areas (rock closest to camera) the detail is too dark to see. By changing the exposure to positive 3 (taking the image up 3 stops) the detail in the dark areas becomes visible. However, you lose the detail in the light areas because it is now too bright to see.
| Original image 0 exposure | Same image Exposure adjusted to positive 3 |
| (click for larger image) | (click for larger image) |
How Your Image Is Displayed
The Viewer has other sliders that you can use to specify how your 16-bit OpenEXR image is displayed on your 8-bit monitor:
Openexr Viewer Ubuntu
- Exposure - sets the apparent exposure of the image on the display. It lightens or darkens the displayed image, allowing you to reveal detail in the high or low end.
- Defog - subtracted from pixel values to compensate for fogging due to stray light in the recording device.
- kneeHigh and kneeLow - pixel values between kneeHigh and kneeLow set the white level of the displayed image, determining which value is mapped to the maximum intensity of the monitor (exrdisplay lets you set the white level between 3.5 and 7 f-stops above middle gray).
The actual process for conversion from raw data to data ready for the display card happens like this (as taken from comments from the exrdisplay source code):
Openexr Viewer Mac
- Compensate for fogging by subtracting defog from the raw pixel values.
- Multiply the defogged pixel values by 2(exposure + 2.47393).
- Values, which are now 1.0, are called 'middle gray.' If defog and exposure are both set to 0.0, then middle gray corresponds to a raw pixel value of 0.18. In step 6, middle gray values will be mapped to an intensity 3.5 f-stops below the display's maximum intensity.
- Apply a knee function. The knee function has two parameters, kneeLow and kneeHigh. Pixel values below 2kneeLow are not changed by the knee function. Pixel values above kneeLow are lowered according to a logarithmic curve, such that the value 2kneeHigh is mapped to 23.5 (in step 6, this value will be mapped to the display's maximum intensity).
- Gamma-correct the pixel values, assuming that the screen's gamma is 2.2.
- Scale the values such that middle gray pixels are mapped to 84.66 (or 3.5 f-stops below the display's maximum intensity).
- Clamp the values to [0, 255].