Tips & Techniques - Highlight Tone Priority

For us Canon users and D-Light Control (I believe) for the Nikonites is a feature that can be found on the more recent bodies..

I mentioned about this feature on a forum recently and it was suggested that should feature as a blogpost - so here you go Calum!!

Firstly, I did a little bit of web searching as you do to check it out - it is remarkable how little information there actually is around. Which suggests that either people don't know what it is for, don't use it much, or that anyone has been that much interested in it.

Well I am no techno geek when it comes to some of these finer points - I use what is available to me, and try to find out it's limitations.

Using the Canon 1Dmk111 as an example, Highlight Tone Priority (HTP) can be found in the Custom Function setting, in the second group under Image/Flash exp./Disp and scroll through to C.Fn 11. You have the option to enable or disable.

I leave mine as disabled unless I am working in certain lighting and subject conditions.

So what does the manual advise us?

By using this setting, we will get improved highlight detail. The dynamic range is expanded from the standard 18% grey to the bright highlights. The gradation between the greys (or grays if you are US I guess) and the highlights become smoother.

There is a caution that with setting 1 (i.e. enabled) that noise in the shadows may be slightly more than usual.

The main visual clue is that the ISO setting on the top plate goes from upper case to lower case on the zeros. So for example ISO 400 with the HTP setting will appear as ISO 4oo. The minimum ISO becomes ISO200, as the camera is effectively carrying out a split exposure processing between the areas above and below 18% grey.

I understand that the selection of this feature will affect frame rate or buffer capacity, although I cannot confirm that from my own experiences.

Here is a bit of info I cribbed from a Google search which is attributed to the fine work by Arthur Morris on his BIRDS AS ART blog

"Canon has not publicly disclosed all the details of the method used to achieve Highlight Tone Priority. I can confirm that Canon’s method involves lowering the gain on the image sensor and modifying the image processing algorithm to simulate the ISO speed set by the user, but the details of the algorithm are confidential. Since HTP does involve lower gain than standard camera settings, it affects both RAW data and JPEG images. Although it would be possible for users to come close to simulating the effects of HTP for RAW images by shooting at a lower ISO speed and altering the tone curve of the image during post-processing, this method requires advance planning and furthermore offers no advantages in terms of noise reduction compared to setting HTP on the camera. Finally, as stated in the camera instruction manuals, “noise in the shadow areas may be slightly more than usual” when HTP is activated. Therefore, it’s basically up to users to decide if the benefits of HTP outweigh the potential drawbacks.” - all as written by Chuck Westfall of Canon USA

So does it work in RAW and jpeg. It clearly works in jpeg, and I understand to get the best of the results you should process your RAW images via Canon's own Digital Photo Professional software (DPP). This would make sense as the the software is designed specifically for Canon files.

Does it work with Adobe products to get the full benefit? Maybe somebody can answer that one. I do understand that it works correctly with Breezebrowser Pro - but you all know that Dave and I are big fans of that particular software.

Here are a couple of image that with and with HTP on. I used manual exposure to ensure that the settings remained the same. Certainly on the back of the camera, the black 'blinkies' were showing on the version that didn't use HTP. You will note that the shadows are clipped on both versions from the little blue triangle.

The main thing to note though is the shift leftwards of the highlights on the histogram with the HTP on version., and that the red clipping warning is extinguished on that version.

So when and where would I use it?

Bright light conditions, with very light subjects - so Egrets for starters, plus Kingfishers in the sunshine, when the sun is beating down on their white neck patch Calum :-).

When wouldn't I use it? - the rest of the time - as I said before I set it to default OFF.

So try for yourself and see what you find.

Without HTP (blown highlights)

With HTP on (clean highlights)

Martin

Techniques-Metering my way

Firstly there is no right way of metering a scene, As long as you get the right exposure in your image whether using Manual, Evaluative/matrix, Spot, Centre weighted or whatever its the final image that matters, I know that Martin is a fan of manual metering where he sets both shutter speed and aperture as he mentioned in his post, Well i am a fan of using AV and matrix metering where i set the aperture and control the depth of field but i allow the camera to set the shutter speed although i control this by using exposure compensation if needed, When i used the Canon 1D MK3 i used to start by flicking on the live view feature and view the live histogram,check this and adjust as needed, This way i knew that when i took a shot the exposure would be spot on, A great feature and one i really miss on the Nikon,These days Camera metering is extremely accurate and using both the Canon and Nikon systems i can say that the Nikon system is between 1/3 and 2/3 of a stop better in keeping whites from blowing, I noticed this when shooting side by side with another Canon photographer who was compensating more than me to stop his whites from blowing, This all helps when processing meaning that you need to adjust less to bring the whites or shadows up, I do in certain circumstances use manual mode,These would normally be in heavy snow where i set the camera to manual and spot metering, After i have set the aperture that i want i will then take a reading off of the snow and add 2 stops, This keeps the whites nice and white, I always do a test shot after setting up and then compensate as necessary, I also use manual when shooting at night for badgers, Here i am using flashguns to emualte daylight and know that the light will be constant which is the important thing when using this mode, I have in the past used manual mode in constant light for birds in flight but this is more of a whim for me as i get just as good results using AV, When i set up for manual like Martin i tend to look for a mid toned object (doesn't have to be grey-Could be mid Red,Blue,Green) and meter off of that but if you understand tones you can meter off of parts of the sky and add +2/3,Off of a white subject like a cloud and add between 1.5 and 2 stops or even off of a black subject and take away 2 stops, Its all down to the tone, The histogram that you get with a digital camera is your best friend along with the flashing highlights you should always have a correct or near as damn it exposure, I am a fan of exposing to the right and started to slightly over expose my images before i had ever read about it, It started when shooting Chamois in snow, By slightly over exposing but making sure i didnt blow the whites i noticed that i had better detail in the dark fur, You need to learn to read a histogram and understand what the tones are that are in it, By exposing to the right you are making sure that the maximum amount of tones are present in the image and can then adjust the exposure in processing, Adjusting slight over exposure doesnt cause grain to appear in the final image but bringing up a dark exposure does,This becomes more important when using high ISO where grain can start to show, Careful exposure means that there will be less processing and as such less grain, Once you have used your choice of metering for a while things will start to come naturally and when you look at your subject say a swan you will know of using AV/Evaluative metering that you will need to compensate by say -1/3 or -2/3 to stop the whites blowing-practice,practice and then practice some more and keep an eye on your best friend-the histogram

Dave