Canon Highlight tone priority – usefull for raw shooting?

Highlight tone priority, HTP, is a feature from Canon with the goal to preserve highlights. From the Canon EOS 6D manual:

”Highlight details are improved. The dynamic range is expanded from the standard 18% gray to bright highlights. The gradation between the grays and highlights becomes smoother.”

With HTP enabled, the lowest ISO will be ISO 200 (D+). What it does is to under expose 1 EV to prevent higlights from clipping. The camera will then brighten the JPEG before it is saved onto the memory card. ISO 200 (D+) seems to be the same as ISO 100, but the camera exposes as it would have done if ISO 200 was used.

For JPEG only?

Raw wise there seems to be no difference if you shoot ISO 100 or 200(D+), ISO 200 or 400(D+) etc. With a Canon EOS 6D the ISO settings ISO 50, ISO 100 and ISO 200(D+) have no difference in dynamic range. With the same shutter speed and aperture, the same amount of highlights are clipped.

To me it seems that Highlight tone priority most likely is for JPEG users.

Below are two sample files. They have been analyzed with Hraw. The same shutter speed and aperture have been used. The one at the bottom has had Highlight tone priority turned on.

Highlights clipped at ISO 100
Highlights clipped in the raw file. Settings: ISO 100, f/7.1 and 1/200 sec
Highlights clipped at ISO 200(D+)
Highlights clipped in the raw file. Settings: ISO 200(D+), f/7.1 and 1/200 sec.

As you can see, there is no difference in clipped highlights more than some movings objects like white birds.

But there is a difference between the files in my raw converter

That is probably due to the Exif tag HighlightTonePriority. If it is set to On, then some raw converters like Canon Digital Photo Professional and Lightroom apply a different tone curve. Below I changed the tag from On to Off and Canon Digital Photo Professional now treats the ISO 200(D+) as if ISO 100 had been used.

Left image, ISO 100. Middle image, ISO 200(D+). Right image, ISO 200(D+) with HTP tag set to Off in Exif.


For Lightroom the preview images use the embedded ones from the raw files.

Preview in Lightroom. Left image ISO 100, middle image ISO 200(D+) with HTP tag set to Off, right image ISO 200(D+).
When moving from preview to develop, Lightroom reads the HTP tags. The middle image ISO 200(D+) with HTP tag set to Off is now treated like the left image, ISO 100.

When comparing the highlights reconstructed by Lightroom there is no difference between ISO 100 and ISO 200(D+).

Lightroom and ISO 100 file. Exposure slider set to -2.
Lightroom and ISO 200(D+) file. Exposure slider set to -3 instead of -2 to compensate for the +1 brightness added in Lightroom due to HTP tag.


darktable doesn’t care about HTP tag.


RawTherapee tries to imitate the embedded JPEG with a tone curve no matter if HightlightTonePriority is set to On or Off. It is possible to disable the tone curve.