Highlight Tone Priority - Useful and why ISO200?

Andreq · 28th March 2008

Played around with my friend's 40D and took a fair bit of shots.

Does anyone know why with the Highlight Tone Priority, the ISO has to be set at least to ISO200?

And do you all find the feature useful? I took shots with and without it turned on. Ermm... Can't really tell the difference leh... I find Sony's Dynamic Range Op more

CS TAN · 29th March 2008

The link to the article is posted below for anyone thats wants to read the section on HTP.
http://www.robgalbraith.com/bins/con...id=7-8739-8970

Quote from RG,

"A Highlight Tone Priority image is processed differently in the camera, regardless of whether the camera is set to CR2 or JPEG. Specifically, the amount of gain applied during the analog-to-digital conversion step is less. For instance, if the camera is set to ISO 200, the amount of gain applied is similar to or the same as ISO 100, which means more of the highlight detail captured by the sensor is preserved during this early in-camera processing step. This is the main reason the camera can't be set lower than ISO 200 when Highlight Tone Priority is enabled; it requires the extra highlight headroom it gets by applying a level of analog signal boost to the sensor data that is commensurate with a lower ISO setting.

After that, it's all secret sauce: Canon isn't publicly describing what is done to the image once it's in digital form, but it obviously involves a modified tone curve that's meant to give Highlight Tone Priority ON photos the same overall tonal look as Highlight Tone Priority OFF ones, but with more detail and smoother gradation in the highlights."

28th March 2008	#1
Andreq Member Join Date: Jul 2007 Posts: 91	Highlight Tone Priority - Useful and why ISO200? Played around with my friend's 40D and took a fair bit of shots. Does anyone know why with the Highlight Tone Priority, the ISO has to be set at least to ISO200? And do you all find the feature useful? I took shots with and without it turned on. Ermm... Can't really tell the difference leh... I find Sony's Dynamic Range Op more

29th March 2008	#2
CS TAN Member Join Date: Sep 2007 Location: West Posts: 2,133	Re: Highlight Tone Priority - Useful and why ISO200? The link to the article is posted below for anyone thats wants to read the section on HTP. http://www.robgalbraith.com/bins/con...id=7-8739-8970 Quote from RG, "A Highlight Tone Priority image is processed differently in the camera, regardless of whether the camera is set to CR2 or JPEG. Specifically, the amount of gain applied during the analog-to-digital conversion step is less. For instance, if the camera is set to ISO 200, the amount of gain applied is similar to or the same as ISO 100, which means more of the highlight detail captured by the sensor is preserved during this early in-camera processing step. This is the main reason the camera can't be set lower than ISO 200 when Highlight Tone Priority is enabled; it requires the extra highlight headroom it gets by applying a level of analog signal boost to the sensor data that is commensurate with a lower ISO setting. After that, it's all secret sauce: Canon isn't publicly describing what is done to the image once it's in digital form, but it obviously involves a modified tone curve that's meant to give Highlight Tone Priority ON photos the same overall tonal look as Highlight Tone Priority OFF ones, but with more detail and smoother gradation in the highlights."