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Tone Mapping - Why do we need it?

Updated: Oct 11, 2021

Tone Mapping is a critical concept when we are working on applications requiring high dynamic range images.


Real world scenes have very high dynamic range that exceeds the electrical dynamic range of the imager. With the current technology, we have sensors as well as ISPs that enables to capture images at far higher dynamic range. However, we are limited by lower dynamic range of the display devices. In order to reproduce HDR images on low dynamic range display devices, capture high dynamic range should be compressed to available range of the display device. This is called tone mapping.


Please find below image - on the left is the original image and on the right is the processing image with tone mapping implemented.


For example, the typical LCD monitor has contrast ratio of 1000:1. However, the contrast ratio of an HDR image is around 250000:1. When we display the HDR image on the display, we end up losing the contras as well as details. Tone mapping process is essential to be able to display the images with the details and contrast retained.


There are 2 main types of tone mapping methods :-


1. Global Tone Mapping – In this method, the tone mapping function is applied to all pixels.

2. Local Tone Mapping – In this method, the tone mapping function is spatially variable based on the neighborhood of the pixel.


Global Tone Mapping is computational simple but results in loss of contrast and detail. However, Local Tone Mapping, being spatially variable, allows us to increase the local contrast and the visibility of some details of the image. Local Tone Mapping usually yields more pleasing results.


When we are working with a camera that support HDR capture, we have to either look at the on-board Image Signal Processor’s (ISP) capability to perform tone mapping process. If not, we have to accommodate the same on the application running on the host.


Based on your application and use case, Regami solutions shall be able to recommend the right camera solution to use. We shall be able to configure the solution based on ISPs from On Semiconductor, Omnivision, etc. with tone mapping implemented in the firmware.


Please feel free to get in touch with us in case of any queries.


Cheers

Sarvesh Rajagopal

sarvesh@regami.solutions


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