Hello all Canon Experts... I have a quick question regarding the Highlight Tone Priority setting in recent Canon Cameras. From what I understood (PREVIOUSLY) this setting ( D+) would lower the high end of the exposure IN CAMERA and help prevent blowing out the highlights of an image. I usually shoot in RAW and almost always have this setting turned on in camera as I often shoot very contrasting wildlife such as Bald Eagles... While talking camera stuff with a friend who is very knowledgeable and who I respect very much as a photographer - he told me that Highlight Tone Priority only works if you shoot in JPEG or use DPP in post. He also showed me a test he did comparing a RAW file and a JPEG shot with same settings to prove his point. This completely goes against everything as I thought D+ was an IN CAMERA function and executed this function during capture... and not exclusively a post production thing. Can anyone shed some light on this subject?....Im just looking for some confirmation one way or another...
Thanks in advance - Scott
My understanding is the same as your friend. It is just a jpeg adjustment. However, I have read reports from photographers who say to leave it on even though they are RAW shooters. One example I've read is from Arthur Morris but then again he uses DPP/PS workflow so maybe that has to do with it. I don't think it really changes your RAW file IF you are shooting in M mode. However, it may change the metered exposure in the semi-auto modes to protect the highlights??
My understanding is that Canon's HTP really does change RAW values. Thsi is what Canon says : • Highlight Tone Priority will be applied (if set in-camera) to RAW if they are processed in Canon’s Digital Photo Professional software;
• HTP is usually ignored if other third-party software is used to process EOS RAW image files, even if HTP was set in-camera
I read somewhere that DPP reduces the highlights while ACR applies +1 EC so it looks like the highlights are still gone until you start recovering them with levels and curves. Nothing certain though.
One thing I noticed is that if you have the ISO set for 100, enabling the HTP will set the ISO automatically to 200 and that will influence the raw capture.
Socrate
It seems to me that it must change the Raw file. If you enable HTP, the ISO is doubled. That affects the shutter speed or aperture, so that your exposure is halved in order preserve the highlights.
Thank you all for your responses...
I usually expose for the whites if Im shooting Eagles or something with such vast differences...but thought I was giving myself a little more wiggle room in post by enabling HTP in camera. Im no way technically savy but thought, ( made up), that maybe Canon put on some kind of limiter on the high end of the exposure to assist in not blowing them out...almost like exposure compensation but only in the last 25% of the right side of the histogram... Im not smart enough to know that this could not be done...but hopeful enough that this could be a possibility.. :>
I may have to call Canon on this one to get verification of what the dealio is.
...Until then, looks like Adobe CC will remain my best friend for the times Im a little too hot on my shots...
Check out my stuff on Flickr - DTT67 (or hit the little Flickr button on here)
The fact that it forces base ISO to 200 is what got me to stop using it. I didn't notice much (or any) difference when I stopped using it, except I could go down to ISO 100 now.
Shasoc wrote:
My understanding is that Canon's HTP really does change RAW values. Thsi is what Canon says : • Highlight Tone Priority will be applied (if set in-camera) to RAW if they are processed in Canon’s Digital Photo Professional software;
• HTP is usually ignored if other third-party software is used to process EOS RAW image files, even if HTP was set in-camera
If you read this carefully, it pretty clearly tells us that the raw files are not changed when you shoot with HTP. If they were, the changes would also be visible (not "ignored") in the third party software.
What is almost certainly happening is that once the files are out of the camera and on your computer, the DPP software recognizes the settings that were in place in camera and applies them as the default conversion settings to the otherwise intact raw file.
It is DPP that is applying the changes. They are not in the raw files.
How exactly are highlight tones saved if the Raw file is not changed? It seems obvious that the HTP reduces the exposure by half, thus actually saving highlight tones. If the Raw file were not affected, then there would be no benefit to HTP. The difference between using HTP and cutting the exposure by half manually is that HTP applies a post-exposure software adjustment so that it looks as if the exposure is the same as if you had not used HTP (but with better highlights). If you do it manually, the image just looks darker until you brighten it manually.
gdanmitchell wrote:
If you read this carefully, it pretty clearly tells us that the raw files are not changed when you shoot with HTP. If they were, the changes would also be visible (not "ignored") in the third party software.
What is almost certainly happening is that once the files are out of the camera and on your computer, the DPP software recognizes the settings that were in place in camera and applies them as the default conversion settings to the otherwise intact raw file.
It is DPP that is applying the changes. They are not in the raw files.
Dan
May be you need to read it more careful, Dan It says usually ignored. In addition for what I understood, ACR doesn't ignore it. When it recognize an HTP it adds 1 +EV to the RAW. In other words recreates an exposure as if HTP wasn't used.
Socrate
Again, the fact that it can be "ignored" almost certainly means that the unaltered original raw data is in the file, and the setting for possible application of HTP or HTP-like alterations are merely applied to the raw file. Those applications that don't understand the setting or those that give the user the option do, in fact, "ignore" it.
"Careful reading" (ahem) of the language you refer to strongly indicates that some but not all conversion applications understand this secondary data that accompanies the raw data. Those applications that do may give you a choice of whether to apply it to the raw file or begin with the unmodified raw data.
Initial raw files are proprietary and may include specialized setting data. The only version that is "standardized" is the Adobe DNG file, which also makes allowance for inclusion of proprietary data beyond the basic sensor data.
Dan
Shasoc wrote:
May be you need to read it more careful, Dan It says usually ignored. In addition for what I understood, ACR doesn't ignore it. It add +EV to the RAW. In other words recreates an exposure as if HTP wasn't used.
Socrate
Max_Pain wrote:
The fact that it forces base ISO to 200 is what got me to stop using it. I didn't notice much (or any) difference when I stopped using it, except I could go down to ISO 100 now.
When using HTP the image is actually captured at a lower ISO, and then the darker areas of the image are digitally lifted to bring their brightness to the same level they would be at without HTP enabled. That is why, when HTP is enabled, you cannot select a ISO lower than 200. When you are shooting at ISO 200 with HTP on, the camera is really recording the image at ISO 100. If you shoot at ISO 100, there is no lower ISO for the camera to use for that underexposure, so HTP mode is not possible.
I always turn off functions that I will never use. Some think that by turning off functions we don't use it will make the camera react quicker. Not sure if this is true or not.
What actually happens to the raw file is quite unclear. One source (http://www.rawdigger.com/node/280) quotes Canon's Chuck West as saying that it does affect the raw file:
"ALO does not affect RAW image data. It is at its best for in-camera JPEGs shot in extremely contrasty lighting conditions. Examples would include backlit portraits and urban landscapes on sunny days, where the tops of buildings are brightly illuminated by the sun but subject matter at street level is in heavy shadow. HTP affects RAW data as well as in-camera JPEGs. It is very useful in high-key shooting conditions such as wedding photography and certain kinds of sunsets. ALO can be combined with HTP with cameras that have both features."
But then, another post on the same page quotes a Canon document that seems to disagree:
"• Highlight Tone Priority will be applied (if set in-camera) to RAW if they are processed in Canon’s Digital Photo Professional software
• HTP is usually ignored if other third-party software is used to process EOS RAW image files, even if HTP was set in-camera"
This would strongly imply that the raw data itself is unaffected, but that some processing values are recorded and may be applied at the time of raw conversion.
It is a confusing mess!
In any case, if it is affecting raw files, it is basically just applying a different curve to the exposure. It cannot actually increase the dynamic range. So if you leave it off and reduce the exposure you can apply your own curves in post and accomplish the same thing.
Why don't we simply try it out and see if dpp does anything sensible to the file or if it's just a PP trick that can be performed manually on LR as well. I would test it right now if it weren't 2am and time to go to sleep...
rabbitmountain wrote:
Why don't we simply try it out and see if dpp does anything sensible to the file or if it's just a PP trick that can be performed manually on LR as well. I would test it right now if it weren't 2am and time to go to sleep...
That's what I've been thinking today. (It is a low priority for me since I don't use HTP.)
HTP is simply an underexposure by 1EV. This underexposed image goes to the RAW file.
The rest is done by the RAW develpoper software applying a special tone curve. Not only DPP is aware of HTP but also ACR does (Photoshop, Lightroom).
The underexposure is done via ISO because otherwise Canon would either need to touch aperture or exposure time - which of course is a no go.
It also explains why ISO 100 is not available when HTP is on - they can not go down 1EV from ISO 100 (in hardware).
There's a simple test to check: create two images with same content, aperture, exposure time, ISO, WB - one with HTP on, one with HTP off. Make sure highlights are not clipped (otherwise you'd have a hard time to compare histograms later). Then just compare the histograms of those two RAW files by using Rawdigger and you'll see exactly a difference of 1EV.
