Understanding HDR from a photographer's perspective.

[Helen B]

But... i still maintain my personal view that HDR as it relates to us photographers (and not computer game designers or graphic artworkers) can be used to discribe the tone mapped representation of the finished HDRI.

I'd like to clarify what I am trying to say here: I see nothing very wrong with the generic term 'HDR' for LDR renderings of HDR-originated images, or even calling things 'fake HDR' - it's an easy shorthand. As I understand it this thread is, however, specifically intended to go further than that loose, almost meaningless description. That's why I suggested that, if you wish to explain things, it may be worth being clear about the role of tone mapping because it is tone mapping that gives most photographic 'HDR' images their characteristic appearance. Moglex did, after all, invite further contributions: "I hope it will stimulate discussion and perhaps others will want to expound on some of the deeper technicalities."

Best,
Helen

 

[Moglex]

Helen is right that without the full luminance values the tone mapped output file is tachnically not a true HDRI.
But... i still maintain my personal view that HDR as it relates to us photographers (and not computer game designers or graphic artworkers) can be used to discribe the tone mapped representation of the finished HDRI.

How else would we as photographers share our HDR images?.... we couldn't.

It would be way too painful to have to go around correcting everyone who displays thier HDR images.... and to give thier images a different name... and what would those images be called?.... this is where a huge amount of confusion would begin....

A guy uses 1 RAW to create an 'HDR'... this can be called tone mapping as all the information used to create the image came from 1 file...

Another guy used 7 exposures to create a HDR.... your going to tell him his image is merly tone mapped as well?.... it may (very) technically be true but if the image was a representaion of the actual finished HDRI he has at home (provided he used all the correct methods) then how can it not be called a HDR?.... it would be very confusing to put this in the same basket as the example above.

Anyway, this is my thinking towards the subject and i have maintined this idea for over 2 years when i first started to experiment with HDR... untill another term is invented to name a tone mapped representation of a true HDR... i will continue to use these terms as i see them.

You are taking a sensible, pragmatic, approach.

It's the only way to deal with these things.

Many years ago people used to drive me to distraction by using the wrong term to describe something. I soon realised that trying to stem the tide was merely tilting at windmills.

If a 'mainfarme' was originally a name that refered to a box containing the CPU and possibly the memory and its antonym was 'peripheral' rather than 'mini' or 'micro', once sufficient people started using it in its more recent sense it was pointless trying to tell them all they were wrong.

This particular subject is complicated because HDR, as used by photographers, is fundamentally different to HDR as the term was originally defined.

There is a very significant extra process that the software must put the image through to create what we call an HDR result that simply does not exist in HDR in the original sense.

This is something that neither Helen B nor Bifurcator seem to be aware of - they certainly haven't mentioned it when defending the original definition of HDR even though it seperates photographic HDR in a very fundamental way.

 

[Moglex]

I'd like to clarify what I am trying to say here: I see nothing very wrong with the generic term 'HDR' for LDR renderings of HDR-originated images, or even calling things 'fake HDR' - it's an easy shorthand. As I understand it this thread is, however, specifically intended to go further than that loose, almost meaningless description. That's why I suggested that, if you wish to explain things, it may be worth being clear about the role of tone mapping because it is tone mapping that gives most photographic 'HDR' images their characteristic appearance. Moglex did, after all, invite further contributions: "I hope it will stimulate discussion and perhaps others will want to expound on some of the deeper technicalities."

Actually, it is not simply tone mapping that gives HDR it's distinctive appearance.

There is a further process in photographic HDR that is fundamental to producing the results we see but which neither you nor Bifurcator seem to be aware of.

Your description of HDR as used by photographers as 'loose, almost meaningless' is just a rather petulant way of disagreeing with the stance that Arch has so sensibly taken.

Photographic HDR has a clear and consistent meaning which is well understood by photographers.

It is simply pointless to try and insist that photographers are misusing a term which once had a single, somewhat different scientific meaning but which has now bifurcated into two terms that are not easily confused because of their wholly different applications.

 

[Bifurcator]

@Helen,
That's how I see all threads where the person is specifically asking about HDR from a state of confusion.


It's not a case of both sides being right. It's a case of fact vrs. fantasy. But like Helen, in regular discussion if the photo-group wants to misuse a term or two it's no sweat to me. As long as they don't start calling cameras WMDs I'm good.

 

[Helen B]

I'm sorry. I really wasn't trying to be condescending.

When you posted:



It really did demonstrate that you are confused about the part played by resolution and the part played by range and how they interrelate.

I shall cease trying to discuss the matter with you so as not to cause further offence.

You won't leave it alone, will you? As you still maintained your stance that you are right and I am wrong in two posts after I suggested discontinuing the discussion, I'll explain my point further. I do realise that there is a link between range, detail, tonal resolution and bit depth - in fact there are a number of my posts on the web about that issue, particularly as I am interested in making prints with a very high density range (in excess of 2.5 OD) that are challenging for 8 bpp printing systems.

Nowhere in you original post do you mention bit depth. Bit depth has a lot to do with shadow detail and shadow tonal resolution, but rarely causes a problem with highlight detail - it was the mention of loss of highlight detail that suggested to me that you were referring to a dynamic range problem rather than a bit depth (tonal resolution) problem.

If the sensor has an adequate dynamic range (ie the shadow and highlight luminances are clear of the sensor's threshold above the noise floor and saturation values respectively) then the ability to record detail in the shadows, but not the highlights, will be limited by the bit depth of the ADC (not always the sensor itself, but I appreciate that you are using 'sensor' to mean the sensor-ADC combination, as is common practice). The over-riding factor is that the sensor must have adequate dynamic range.

Best,
Helen

 

[Moglex]

@Helen,

There's a PM facility for personal messages.

That's how I see all threads where the person is specifically asking about HDR from a state of confusion. It's not a case of both sides being right. It's a case fact vrs. fantasy.

All you are saying here is that you are taking a dog in a manger approach and insisting that you and only you are correct when that simply isn't the case.

You are insisting that HDR means one thing: a specific scientific meaning that cannot really relate to photography as practiced by the members of this group since there is no current, practical, way to display the result.

In actual fact the term long ago bifurcated to mean, in addition to its original meaning: a series of processes to allow an photographic output to represent a Higher Dynamic Range than it would otherwise be able to. (Personally I consider the 'dynamic' to be little more than a noise word originally included to make the TLA more impressive :mrgreen.

I wonder what sort of a state you get into when someone used the term 'ATM' to mean 'Asynchronous Transfer Method'.

Do you jump up and down telling them that it means 'Adobe Type Manager' (or Automatic Teller Machine) and they are living in a fantasy world?

 

[Bifurcator]

What if you did not tone map the HDR image?

Could you post an example of a before tone-map and after tone-map image please?

Thanks.

This is an EXR formatted HDR: http://tesselator.gpmod.com/Private_/PICT4482_PIZ_hdri.exr Load this into CS3 or another HDR editor (there are many) and select the exposure tool. Load it into Photomatrix and look ad the HDR histogram or use the exposure up/down tool in Photomatrix.


Had I saved it as a Radiance file it would have an .hdr file extension - as HDR is a file format. The difference between EXR and HDR is that the EXR format has more compression options, it's a little more robust (in terms of options), and it's an "open" file format meaning us developers can get twisted. See: www.OpenEXR.org


And here's the tone-mapped jpeg as requested:

 

[Helen B]

As we're all chatting away so nicely here, I'd love to see some of Moglex's photos. Where might I find some on the web? That's what photography is all about, after all, and it helps to give a perspective.

Many thanks,
Helen

 

[Bifurcator]

As we're all chatting away so nicely here, I'd love to see some of Moglex's photos. Where might I find some on the web? That's what photography is all about, after all, and it helps to give a perspective.

Many thanks,
Helen

Is he raising a ruckus again? I still have him on ignore so I can't see anything except what you quote.

 

[Moglex]

You won't leave it alone, will you? As you still maintained your stance that you are right and I am wrong in two posts after I suggested discontinuing the discussion, I'll explain my point further.

Come on now, be fair, you started up again after you said we should agree to differ by arguing with Arch's very sensible post trying to insinuate you were right and everyone else was wrong by using expressions like: 'loose, almost meaningless description'.

I do realise that there is a link between range, detail, tonal resolution and bit depth

Good, that's a start.

Nowhere in you original post do you mention bit depth.

Indeed.

That is because I was trying to make the explanation as simple as possible and it is not actually necessary to refer to bit depth to give a simple explanation of what is going on.

Bit depth has a lot to do with shadow detail and shadow tonal resolution, but rarely causes a problem with highlight detail - it was the mention of loss of highlight detail that suggested to me that you were referring to a dynamic range problem rather than a bit depth (tonal resolution) problem.

If the sensor has an adequate dynamic range (ie the shadow and highlight luminances are clear of the sensor's threshold above the noise floor and saturation values respectively) then the ability to record detail in the shadows, but not the highlights, will be limited by the bit depth of the ADC (not always the sensor itself, but I appreciate that you are using 'sensor' to mean the sensor-ADC combination, as is common practice) {Moglex: "Indeed - as I have said I was trying to make the explanation as simple as possible, not show off my knowledge with irrelevant pedantry"}. The over-riding factor is that the sensor must have adequate dynamic range.

I'm sorry to have to say this and run the risk of getting accused of condescention again, but you still don't seem to realise how 'dynamic range' relates to resolution.

Once again, you inject a raftload of impressive technical sounding terms: "luminances are clear of the sensor's threshold above the noise floor and saturation values respectively" (BTW, I assume you intended below the saturation levels rather than above?), without seeming to grasp the underlying truth:

The sensor is mounted in a camera so it's raw range is irrelevant. What is important is its resolution because that is what determines the amount of shadow detail it can capture at the point that highlight detail is about to be lost.

 

[Helen B]

Come on now, be fair, you started up again after you said we should agree to differ by arguing with Arch's very sensible post trying to insinuate you were right and everyone else was wrong by using expressions like: 'loose, almost meaningless description'.

I wasn't arguing with Arch, I was agreeing with him: "I'd like to clarify what I am trying to say here: I see nothing very wrong with the generic term 'HDR' for LDR renderings of HDR-originated images, or even calling things 'fake HDR' - it's an easy shorthand."

Best,
Helen

 

[Bifurcator]

Wow... a butt kiss to the admin and throwing you under the bus all in the same sentence.

I guess Arch is smarter than that. He types like an intelligent guy anyway. I guess he knows we're all just here trying to communicate our ideas. It's all good, it's all fun, it's all good fun.

 

[Moglex]

Wow... a butt kiss to the admin ...

I guess Arch is smarter than that. He types like an intelligent guy ...

ROFLMAO.

Did you mean to be that funny?

 

[tirediron]

As we're all chatting away so nicely here, I'd love to see some of Moglex's photos. Where might I find some on the web? That's what photography is all about, after all, and it helps to give a perspective.

Many thanks,
Helen

I'll second this.

Moglex you are certainly using some very impressive terminology, and I have to admit that when we start getting into the technical aspects of how sensors actually 'sense' I start to get out of my depth. I'd like to see some supporting references for your statements. Not saying I don't believe you, but I have seen Helen's work and I know from other posts she's made that she is extremely knoweldgable, and I'm more than a little reticent to doubt her.

I'd also like to comment on a statement made earlier in the post refering to the distinctive appearance of HDRs. A properly executed HDR should NOT have a distinctive appearance. Discussions of bit-depth, dynamic range and so forth aside, just because you can produce an image with a mind-boggling dynamic range doesn't mean it's a good image.

 

[Arch]

come on guys.. im sure we are all smart enough to know that disagreeing with someone only makes you learn more about looking at the subject from another perspective, even if you think the other person is dead wrong.... after all disagreeing is where real progress is made... however it doesn't need to get personal... im sure we can all agree that.

So please show a little self restraint and bite your toungs