Conflicting information and opinions

[rpcrowe]

Canon has not done a good job explaining (what's new about that) the concept of Highlight Tone Priority (HTP). As a result, doing research on that term comes up with many different explanations as well as opinions.

The handout provided by Canon during the Summer 2017 EOS Discovery Day (Intermediate 201: Participant Guide, page 23) states the following:

"If bright areas of a scene are over-exposed, you cannot bring back detail later in the computer. Highlight Tone Priority is a custom function on some EOS models that will add detail to the highlights in the image. This can make a big difference when shooting in bright sunlight and other contrasted (sic) light conditions.

It is useful in scenes with contrasted lighting or scenes with whites or light colors in the image, such as a bride in a white wedding dress or a white house. While anyone can bring out detail in bright highlight areas by darkening the entire scene, the difference with Highlight Tone Priority is that it can bring out details in the brightest areas, without darkening mid-tones or shadows"

It goes on to say,

"NOTE: ...if you've activated Highlight Tone Priority, for technical reasons, your lowest ISO setting will no longer be available (in other words, the lowest ISO you can set is 200)."

Watch Rudy Winston regarding HTP on Canon's Digital Learning Center
https://www.youtube.com/watch?v=BuO7mLo_G0k

From what I've read, in my general research, I gather that with HTP enabled, and the ISO set to, say, 200 (the lowest ISO for HTP use) the camera actually reads the analog data for ISO 100 from the A/D Converter/amplifier, then applies a curve in digital processing to boost the exposure for the dark and midtones, while curving down the boost into the highlights. I don't have an expert analysis of this but more opinions of those who've run tests and analyzed the results.

However, nothing is said about the impact HTP has on images captured in RAW...

Do a Google Search for Highlight Tone Priority in RAW and you will come up with three basically different answers, expressed in many different ways...

1. HTP has absolutely no impact on RAW images
2. HTP has impact only on RAW images that are opened in DPP
3. ACR recognizes HTP and will apply HTP "partially" to a RAW image as it opens

It "seems" that when I select HTP and open the RAW image in ACR there is a slight improvement in the highlight tones without much (if any) degradation in the shadows. However, I wonder if I am imagining this or not.

I do know one thing... if you have the blinkies turned on and are using HTP, there will be less blinkie area on the LCD than for a non HTP image. However, that could be explained in that the image we see on the LCD is a JPEG conversion...

[Black Pearl]

Sounds like they've 'nicked' Fuji's DR trickery which works in exactly the same way. In the case of Fuji you select 400iso for DR200 and 800iso for DR400 (base is DR100 at 200iso) and the camera does exactly the same as Canon describe. It meters for the selected iso then instead of applying a universal gain to the data boosting it all from base it applies a curve lifting the darker areas more than the highlights.

Now I know with Fuji this DOES affect the raw files and that most raw converters will read the EXIF and apply a similar correction when they initially preview the file. They don't seem to do exactly the same as the Fuji's in-camera processor when it creates a jpeg so you need to experiment to find what your combination can achieve and expose/process your files accordingly.

When I have my X-T1 set to Auto ISO I tend to have Auto DR running as well because the camera does a remarkably good job at selecting the right combo to keep the available dynamic range sitting nicely within the scene I'm shooting. When I'm shooting more carefully and have a fixed iso (typically base) then the DR mode doesn't activate and when I lift the iso manually I'll decide from shot to shot whether I want to use DR boost.

[Manfred M]

I was going to suggest this sounds a lot like Nikon's ActiveD Lighting that has been around for a long time. Curves are applied at the shoulder and heel of the data to allow more data to be shown in the extreme highlights and extreme shadow areas to produce more detail and reduce areas that are clipped or blocked. My Panasonic video cameras have similar functionality.

This does work, but on Nikon at least, only in the jpeg output, but as Robin has pointed out, to get that effect, the camera changes the raw capture and "compromises" that in order to produce more acceptable jpegs.

I don't use this functionality as I prefer making my own corrections in PP by creating the curve that works best for the scene, rather a generic calculation done by the camera.

[DanK]

I never use this, so I may be off base, but my understanding is that HTP drops exposure by one stop by changing ISO (which is why it can't be used with base ISO) and the expanding the highlights, basically giving you highlight detail at the expense of compressing shadows. One can do this easily without HTP: expose a stop to the left and expand the highlights in post. According to Chuck Westfall, HPT, unlike ALO, does affect the raw image: http://digitaljournalist.org/issue0902/tech-tips.html..

[rpcrowe]

Canon also has Auto Lighting Optimizer (ALO)

http://cpn.canon-europe.com/content/...g_optimizer.do

From my research, ALO is somewhat akin to Nikon's Adaptive D-Lighting.

https://digital-photography-school.c...ing-optimizer/

At least Canon provides the information that ALO can be used with RAW captures if those captures are processed in Canon DPP. However, it doesn't mention that ALO is "ONLY" compatible with RAW captures if those captures are opened in DPP.

It appears that when processed in DPP the ALO brings out shadows while the Highlight Tone Priority (HTP) works on the highlight areas.

Although, I do like achieving the best image possible in-camera to minimize the post processing necessary, I would certainly not want anything that I did not control to work on my RAW files. The great advantage of a RAW file is that it is just that - RAW. I can then apply any PP I desire in any magnitude but, I will still have the RAW file virgin and unmolested on my hard drive.

OTOH... (and that's a big other hand) since the image you view on the LCD is generated by a JPEG - using either of these "tricks" might come closer to showing you what you "could" get with a RAW image "after" some post processing.

I guess, as always, I will have to do some testing.

I was first introduced to HTP at a Canon seminar where nothing was said about JPEG-DPP-ACR differences. I tried HTP shooting my white coated rescue dogs and it "seemed" to help keep the highlight values in line. However, it could be that I am just used to shooting the white coated dogs and it is my exposure/lighting, rather than any "magic formula" that does the trick.

But, since it doesn't seem to hurt a bit (and may even help a bit), I will keep using it on my RAW images of white dogs. Whether I use it for other types of images, only time and experimenting will tell.

[Adzman808]

Sounds like how the Fuji one works where the camera underexposes by one or two stops, then applies a dark and mid tone brightening curve post ADC to the resultant jpeg file (which is already explained in this thread)

The snag with the Fuji one and RAW is twofold

1) you get more DR at base ISO exposing for critical highlights and lifting shadows in post
2) various RAW convertors interpret the DR function in different ways. For example at one time LR (maybe it still does) would work ok if you’d manually set a DR “expansion” mode, but not if you’d used auto. Another snag on the Fuji system is that the latest bodies (X-T2 etc) won’t give you an accurate histogram in DR auto mode, only manual DR mode. The earlier Fujis wouldn’t show you an DR expanded histogram at all

I appreciate that Fuji is not Canon, and a similar sounding feature doesn’t mean that both brands operate in the same way. But equally my OPINION (so YMMV) is that s/he who shoots raw is best served by doing their own editing and not using the camera jpeg functions. But that’s probably just me!

For jpeg shooters (incl those who edit their jpegs) DR expansion is a really good thing. For RAW shooters not so much

[rpcrowe]

I am going to try to get the answer "straight from the horse's mouth". I will attend an Introduction to Canon EOS Cameras, presented by Canon. Hopefully the Canon Guru presenting the seminar will know about Highlight Tone Priority when shooting RAW and opening in Adobe Camera RAW rather than shooting JPEG or shooting RAW and opening in DPP.
I also hope to find out basically the same information regarding the Lens Aberration Corrections when shooting with the 6D2...
Of course, when I attended another Canon presentation on flash a few years ago, the presented
r did not know that with Canon flash units, with HSS selected, the camera/flash will revert to standard sync automatically when the camera's shutter speed is at or below the camera's maximum sync speed.

[DanK]

A number of times in the past, I have sent technical questions to Canon support via e-mail. In every case but one, they promptly sent a reasonably clear response. The one exception was that I wanted the pupil entry diameter for a macro lens, and they replied that they don't provide that information. You could try that in this case.

Re lens aberration: I'd bet you good money that this is simply metadata and that the raw file isn't changed. Some Canon webpages actually refer to this as a feature of DPP. I don't know whether Adobe's lens profiles make use of this, but I suspect not, since the lens profiles don't adjust for CA.