Film vs Digital - Dynamic Range

[helenbach]

Rishi,

 

Which side of the film do you have against the AN glass for those scans?

 

Thanks, Helen

[rishij]

Mauro:<i>"The glass surface you posted looks pretty bad/horrible. The Nikon glass holder does not have that problem."</i>

<p>

Right but you're using a LS-9000 right? So if your holder had that surface, you wouldn't know b/c the diffuser eliminates the pattern. Or rather, the lack of a collimated light source illuminating the AN glass de-emphasizes the pattern.

<p>

Indeed, when I place an optical diffuser in the path between the light source and the AN glass in my LS-4000 -- the pattern disappears! Results pending a thread on this topic :)

<p>

Helen: the light source on the LS-4000 is on the top. The CCD is below the film. I have the emulsion side facing the CCD with no glass in between the film and the CCD. The base side (shiny side) of the film is facing up, with the AN glass placed above it such that the etched side is touching the base side, and the non-etched side of the AN glass is facing up toward the light source. Hence why I don't get any Newton rings (yet).

<p>

Cheers,<br>Rishi

[mauro_franic]

That is a good point, still that pattern seems large an intrusive though. Yet it could be the difference in the light type.

 

If you want to, I can mail you the Provia frame I used for the ICE test so you can run thorugh your 4000 for comparison.

[tom_kieren]

I'm baffled by the controversies aired here as this is my first exposure to this chat group. I feel like I should get a

Ph.D. in photographic process in order to feel confortable discussing some of these issues.

 

As an architectural/interiors photographer using a Sinar F2 4x5 camera with a roll film back, I and many others in my

professional still use primarily film because either the clients request it (refersing their earlier preference for digital) or

because if it ends up being cheaper to use than a digital front end camera process - given the much greater PS time

and cost (if you charge for it) from using a prof'l level digital camera and related equipment, process. A few more

sophisticated architects can be quite fickle about the use of specific types of cameras (depending on the age or

generation of their art director or the latest buzz about new cameras) but most don't even care which front end

process the photographer uses since all they want is a CD at the end of the process and they couldn't care less how

you acheived it as long as the client's perceived required level of quality is met and evident in the final printed image

in a website, proposal or publication. I know major arch firms that remain 85% film based but even they don't discuss

the issue (as we do) whether film or digital front end equipment and their respective results are "better". It, in my

humble opinion, is very personal, situation specific, and hopefully based on the evidence we photographers have or

don't have regarding what will give the client the best results. Bottom line: what is important is which process gives

you the best level of quality for what the client says he or she needs and later applauds, and thereby also gives you

a competitive advantage in your marketplace. From a purely business point of view, what good is bulking up and

using an expensive digital camera if it doesn't ultimately give you a competitive advantage in the eyes of the

customer?

 

As a result of my limited rentals of digital cameras, my personal observation is that film is still superior to and less

expensive vs. the digital front end process. As an aside, many at B&H Photo continue their argument that "why go

digital when good professional film gives you, right out of the box, the roughly 26mp equivalent - which they add most

digital cameras can't even approximate.... Same for dynamic range, color saturation, three dimensionality". Keep in

mind that my market is to architects and construction companies, publications, designers who have little need

for 'quick turnaround' vs. art directors who want instant feedbacks as in a fashion shoot or daily sports news

newspaper environment. I might also add that the annual NPR NY Times roundtable broadcast "seminar" (by a host

of acknowledged experts) on this topic, still leans in the direction of film in terms of its technical end-results achieved

for a variety of end uses. The debate rages.

 

Having said all that, I hope to make my first purchase of a new Nikon 26mp full-frame DSLR digital camera when it

comes out in a year or so! - so I too can enter the grand experiment you folks are inmeshed in. Keep up the good

discussions. Eventually, I'll figure out a fresh way of identifying what is "right" for my clients' needs as time

progresses, as I start full scale technical experiments and evaluations. All the best. Tom Kieren

[vijay_nebhrajani]

<i>Mauro: "Vijay, film gets more resistant to light the more exposed it gets. I an over simplified example, it is

like walking into a wall,

<p>

With film the closer you are to the wall the shorter the steps you take (yes, you can always linearize later)."

</i><p>

No, yes - I actually understand what you were saying before, I was pointing out that film is actually linear, not

log.

What you are describing now is "soft clipping"; digital has "hard clipping", I suppose, but nothing prevents

engineers from designing in soft clipping either. However, that does not increase the <i>dynamic range</i>. In

fact soft clipping is obtained at the expense of the linear region, and can actually be considered detrimental in

linear systems. I can't for a moment imagine the clipping characteristics to matter much (or at all) for the

purpose of

discussing dynamic range.

<p>

<i>Rishi: "Digital sensors don't do this, AFAIK, because I'm not all-knowing. No one is. Except for Feynman."</i>

<p>

Of course digital sensors do this, and so do all physical systems. As you wind a spring, it gets harder towards

the end (soft clipping), and as you fill up a glass, the last drop causes it to overflow (hard clipping). With

digital sensors, it is a bit of both, depending on the actual circuits, but generally if you consider charge in a

reverse biased photodiode (or photogate) it will clip "soft". Think of how a flash charges - initially it makes a

loud, low pitch sound, and as it gets more and more charged, it makes a higher pitch sound. This is actually the

current charging the capacitors; initially it is high, and as time goes on, it becomes lesser and lesser; this

kind of behavior is called "asymptotic". The charging current asymptotically approaches zero.

<p>

All nice and fun, but doesn't affect dynamic range one bit. Dynamic range is a ratio: the max to min value of

whatever. In our specific case, it is the response of a medium to light. This has little to do with how many bits

you use to represent the values, or how the response varies (log curve, sine curve, who cares). The only thing

that matters is the final max/min ratio. The only exception is if you can actually convert "soft clipping" to

useful dynamic range - unfortunately this barely results in a third to half stop extra with film, and this is

perhaps unavailable with digital. Nevertheless, it is a tiny fraction of the actual dynamic range.

<p>

It would appear that for Ektar 100, Mauro found that this ratio is upwards of 8000:1; 2^13 is 8192, so this is a

dynamic range of upwards of 13 stops. In dB terms, a ratio of 10,000:1 is (since log_10(10,000) = 4) 4 * 20 dB or

80 dB. Digital, with about 9 stops is around 512:1, which is around 55 dB.

<p>

55 dB is quite low, and I am quite sure that the current generation of imagers being designed should have at

least 80 dB or more (I've seen some papers that claim 115 dB) and we will start seeing these sensors come in

fairly soon

- 2-3 years, I think.

<p>

And finally if you want to test dynamic range, you don't have to plot response versus exposure or whatever; just

find two points, one for underexposure and one for overexposure at which detail either disappears into all black

or all white. The ratio of these is the dynamic range. Simple.

[rishij]

Vijay:<i>"The only exception is if you can actually convert "soft clipping" to useful dynamic range -

unfortunately this barely results in a third to half stop extra with film, and this is perhaps unavailable with

digital. Nevertheless, it is a tiny fraction of the actual dynamic range."</i>

<p>

<b>Reference??</b>

<p>

We had the same problem in the binary vs analog thread -- if you're gonna claim something that

goes against observation, you gotta back it up with some explanation for the observation... in this case the

observation being that there's clearly more stops recorded by negative film, yet here you are saying that they

all respond linearly to light. That doesn't explain the observations. Furthermore, if layers of film start

blackening when exposed, how does that NOT lead to a logarithmic response, or a more 'spread out' <i>soft

clipping</i> (in your terminology)? If the film layers get blacker, it becomes harder for photons to penetrate

(b/c they can be non-productively absorbed), which might explain the large latitude of exposure we see... yes?

<p>

Thanks for the example with the capacitor, but please translate that to how it is relevant with a photocell. If

you could explain or point me to a reference for how exactly the photon encounter dislodges electrons, etc.,

that'd be appreciated. Most Google searches lead to non-technical references, which I'm tired of reading.

<p>

Finally, explain to me how, if negative, positive and digital sensors are all linear, why it's almost impossible

to overexpose negatives ('logarithmic' response to light, as I've read, I'm not just making this up, so blame all

the carriers of misinformation out there if I'm wrong), too easy to overexpose positives (exponential response to

light), and digital somewhere in between...??

<p>

Thanks,<br>Rishi

[vijay_nebhrajani]

Nice, Rishi - attack before you research.

<p>

First, a google search of "soft clipping" turns up 38,500 hits if you put the

phrase in quotes, otherwise 870,000 hits. Go read some of them, including the wikipedia articles at the top. My

terminology? You don't know what you are talking about at all, do you?

<p>

Second, don't spread FUD, please. Linearity has nothing to do with dynamic range. The first is the shape of a

transfer curve, the second is a ratio. This thread is about dynamic range, not about linearity. Look at the

thread title.

<p>

Third, a photogate is a capacitor. So is a CCD. Go look up how they work.

<p>

Fourth, you should know better, after interminable arguments in the other thread, that silver halides mostly

don't get

converted to silver until after developing. How is it that silver that doesn't exist block light?

<p>

Fifth, the response of film (black and white, slide, color) is all linear (or closely linear). If you have any

doubts about this, pull up film data sheets and look at the characteristic curves. Then go look up exponential or

log curves.

<p>

Sixth, you asked for references. Here's one. The definition of dynamic range. Look it up. <a

href="http://en.wikipedia.org/wiki/Dynamic_range">http://en.wikipedia.org/wiki/Dynamic_range</a>

<p>

Seventh, don't go off on a tirade of "how" before the "what".

<p>

Lastly Mauro, I really don't want to hijack your thread; but this is a discussion about dynamic range (at least

what I am doing). So if you want me to stop, I shall; and if you are interested in letting me put forward the

reality, I can do that as well.

[vijay_nebhrajani]

References:

<p>

Clipping, hard and soft: <a href="http://en.wikipedia.org/wiki/Clipping_(signal_processing)">Clipping (signal processing)</a>

<p>

Sensor technology: <a href="http://en.wikipedia.org/wiki/Active_pixel_sensor">Active Pixel Sensor</a>

<p>

Pixels: <a href="http://en.wikipedia.org/wiki/Active_pixel_sensor#Pixel">Pixel Circuit</a> - talks about the transistor M_sf - "an amplifier which allows the pixel voltage to be observed without removing the accumulated charge". A device that stores charge is called a capacitor. A zero biased photodiode is essentially a capacitor whose charge is proportional to the light striking the junction.

[vijay_nebhrajani]

References:

<p>

CCD is a capacitor (the light capturing part): <a

href="http://en.wikipedia.org/wiki/Charge-coupled_device#Basics_of_operation">Charge Coupled Device</a>

[mauro_franic]

Here is another example I shot today of some dead roses on the ground with TMX (35mm) where the dynamic range of the scene even exceeded the film! (This was developed with Xtol 60/40. If I had intended to expand the highlights and the shadows pass 15 stops I would have used TMAX developer but I consciously opted to go for the midtones -Xtol- instead).

 

This picture would have been literally impossible with my 40D.

 

http://shutterclick.smugmug.com/gallery/4811519_F9MBv#427771770_c45Yh-X3-LB

[mauro_franic]

Vijay, "What you are describing now is "soft clipping"; digital has "hard clipping", I suppose, but nothing prevents engineers from designing in soft clipping either. However, that does not increase the dynamic range. In fact soft clipping is obtained at the expense of the linear region, and can actually be considered detrimental in linear systems."

 

No offense intended at all, but you are confused. You are thinking like "Photoshop" when you think that changing curves does not affect dynamic range. We are talking about the "effect" a non-linear capture has on the number of stops recorded.

 

In my "walking into the wall example" if you take steps half the distance to reach the wall then how many "steps" can you take? Obviously infinite.

 

In the same example if you take equally spaced steps say 9 (a la 40D) and you hit the wall, yes you can plot the number of steps against the distance using a logarithmic scale if you want to, but pass the last step and before you hit the wall there is nothing.

 

 

And you are probably right that a digital system could be created to have a non linear capture to expand dynamic range. But here we are comparing current existing technologies.

[andrew_hopkins2]

hmm seems italics dont work

 

Quote PHOTO.NET has several main threads that have been rehashed over the last decade many thousands of times.

 

No doubt they have been rehashed Kelly and if you are spending a great deal of time on the forums then you would be sick of it. But as strange as it may seem, digital is new to me (I just shoot film, I have an old 2Mp digital camera that is the size of a house (well maybe a caravan ;) , but its horrible so I never use it, the one on my phone is better). Considering the technology of digital is always advancing, old discussions aren’t as relevant as new discussions. On occasion in the past and again now I am considering buying into digital. But before I consider spending the huge amount of money buying into it and all that goes with it, computers, hard drive storage, scanners, printer, camera, lens, surge protectors and software ect. I would like to know some of these obvious things that are discussed. So I can weigh up whether it’s right for me given the latest improvements and whether I really want to spend the huge money.

 

I can’t say I enjoy these threads that get taken over with all the techno babble at all, but I don’t mind as much so long as someone eventually comes to a straight forward easy to understand conclusion, that I can relate to in everyday use and the finished print. I don’t have the benefit to hire equipment in my location.

 

Quote(1) Folks buy a gooberflex digital and ask how BIG can I enlarge the image.

 

As lame as this type question is, it does make me wonder sometimes as well. When I go to the camera store they have some picture of a scantly clad girl enlarged to 6x4 foot poster and say ,see this is digital. I don’t get much of an explanation out of them how they achieved it (and they usually come from Canon or Nikon reps anyway) so I eventually brush it aside as sales pitch. Another shop told me I am wasting my time with 8x10 large format negs as digital is just as good as that too…I find that impossible to believe and think it is just them wanting to sell me digital equipment. I do get lost and frustrated with biased advice.

 

Quote(2) Folks learn that slides have less dynamic range than a negative.

 

Well I guess if they don’t know they find out by people saying so, even tho some can understand just by looking at the prints others may appreciate the explanation.

 

Quote(3) Folks learn that many digital sensors have a less dynamic range than a negative.

 

That seems to be what this thread is about and just a few posts have been straight forward enough to understand why. I find it useful.

 

Quote(4)Folks learn that a raw digital file can have more range than a jpeg

 

seems obvious

 

Quote(5) Folks who post giant images on the web and learn that they got borrowed and stolen

 

yeah well duh, but basic good advice given inst any skin of your nose

 

Quote(6)Folks who learn that having more ram makes their Photoshop computer work better

 

may seem obvious, but considering I don’t have photoshop its still a reasonable question if i would like to know just how much ram others find that works with the latest release computer, PS and large (files) negs scanned .

 

Quote(7)Folks who learn that a high contrast lens test shot with camera bolted to a granite block give great resolution numbers to brag about.

 

Quote(8) Folks who learn that disc drive can carsh and "learn" that they should havce had a duplicate file

 

its still useful information; it seems to relate to just how huge a cost I will need to spend on raid storage to hold medium and large format files/scans

 

Quote(9) ZILLIONS OF FOLKs who are are lost souls; who crave an exact megapixel equalvalent for 35mm film; often posting results. The same folks probably want and can prove the number of MP3's per 13 year old girl; shoes per woman, lenses per photo.neter, or beers per football game.

 

Like I say I don’t much like all the techno babble and fine nit picking but I do like to know how 35mm, 120, 4x5 and 8x10 film compare in terms of digital. What cameras or formats can be replaced if I go digital and is it cost effective to me ect.

 

Quote(10) Folks who buy a lens with a dinky scratch and ask others if it a matters; but do not have the ability to shoot few frames as their own test

 

yeah well you get that, seems obvious to me as well but who knows what goes on in the minds of others. Maybe they just want to know if it didn’t have any marks would their images look better

 

Quote(11) Folks who crave ratings on posted photos; but complain when they get negative feedback.

 

Doesn’t concern me, I guess its bothers people whom spend more time on the forums.

 

Quote(12) More threads about film versus digital; posted like its a new subject; when its several decades old now.

 

It is new to me, old posts a near irrelevant to me as the comparisons are to older digital cameras. I cant say I appreciate the bickering that goes on , I just want simple straight forward answers on the differences, advantages and disadvantages

 

Quote(13) Folks who discover that scanning takes time; when its a 2 decade old known fact.

 

seems obvious

 

Quote(14) Folks who think that cleaning off fungus from a lens "magically" removes the potholes that are etched in advanced cases of fungus.

 

some people just don’t know, it doesn’t help to dismiss

 

Quote(15) Folks who worry about Macs versus PC's instead of worrying about results delivered to clients.

 

This is actually something I was interested in lately so i read up on it. I am due for a new computer and if I have to spend up to $4000 ish then I would be stupid not to gain information and ask a simple question or read posts on the latest equipment available.

 

 

 

 

[mauro_franic]

Vijay also, "I actually understand what you were saying before, I was pointing out that film is actually linear, not log"

 

 

Please read Ektar's publication. Look at the gain chart... it looks linear right? well now look at the scale it says log.

 

http://www.kodak.com/global/en/professional/support/techPubs/e4046/e4046.pdf

[bernardwest]

<i>No offense intended at all, but you are confused</i><P>

 

Oh Mauro.... now you've gone and done it....

[vijay_nebhrajani]

Mauro - the chart you pointed out to me is that of density vs log-exposure. Density is itself a logarithm. So it

is a log-log chart, meaning that the shape of the curve is exactly as it appears - i.e., linear. Take the inverse

logarithm on both axes - the curve shape won't change one bit. No offense taken, Mauro - please don't take any

when I point out that you are in error here.

 

As for the walking into a wall example, it doesn't apply. You have maybe 13 stops of completely linear transfer

function, and maybe a quarter stop on the top and bottom parts of the S-curve. This half stop is "curved" (just

the knee parts of the curve), akin to your walking into a wall thing. If you were to "straighten" it out thereby

extending the linear range, you could get back that half stop or so. Beyond that, it's all lost, because the film

response has become "flat" - change in exposure results in no change in density.

 

And finally, dynamic range is a simple ratio. Nothing to do with curve shape at all. If you can linearize and

extract an extra half stop, then fine - the dynamic range is now 13.5 stops; that is the final max/min ratio.

Thats all.

[rishij]

Thanks for the references Vijay. Re-read my post -- I was asking for explanations of the observations & references for your broad claim that clipping only saves 1/3 to 1/2 a stop for film. Do you expect us to just take your word for it?

 

And why does it always come down to a game of semantics with you? Previously I had to spend hours explaining to you why perceived resolution and tonal range of the image forming element *were* related, while you simply touted that tonality & resolution are unrelated -- which they are, in the broader sense, but not in the sense we were discussing.

 

Same thing here. Yes I know the linearity, or slope, or whatever of the actual curve *does not have to be related* to the overall range of intensities recorded; HOWEVER, if the response of your light-responding element, which may otherwise be linear, encounters a phenomenon such as darkening of the layers of film to an extent where subsequent penetration of photons become more and more difficult, THEN you would increase the latitude of exposure because in any given spot that, were response entirely linear, would have been entirely exposed so as to result in a fully developed grain but that, now, experienced less productive photon hits and so therefore will stop just short of being fully reduced to a grain of ENTIRELY metallic silver.

 

In which case, exposure latitude of the film would change due to its nonlinear response.

 

Happy?

 

And no, I didn't know the TERM 'soft clipping', though I know very well what it is. I'm not afraid to admit it. What am I an EE? Chemistry & biology, dude, but at least I take a stab at subjects out of my field, so don't poke fun because I don't know your terminology. I'm here to learn & maybe, just maybe, in the process contribute. Your arrogance is truly astounding. When's the last time you picked up a Chem Rev. article like the one I posted and asked you to read in the last thread? Mees? Baines?

 

Finally, you dog me for misunderstanding 'dynamic range'. WTF? Where have I mentioned 'dynamic range' in my post?! I was speaking of 'exposure latitude'. Read before you attack.

 

And while we're on specifics -- fine, it's not a 'logarithmic' response... that's just the term people seem to be throwing around & I jumped on the bandwagon. It's a sigmoidal shaped curve with a toe & a shoulder... i.e. the Hurter Driffield curve.

 

The more interesting question to answer is this: is the greater exposure latitude of negative film due to the shoulder of the H&D curve? And is this shoulder replicated on digital sensors?

 

Finally, Vijay, re: your comment about how silver that doesn't exist blocking light -- don't be a smart alec. How can it? It *can*; now the extent to which it affects exposure, I couldn't tell you (but it's an interesting question I'd like to find out the answer to). We learned from all our research in the last thread that you could have hundreds to thousands of sensitivity specks per grain. Each of these specks could, upon exposure, yield up to 50 or more (I don't think we ever determined the largest number) reduced silver metal atoms clumped up around the sulfide electron trap. Multiply this by all the sensitivity specks per grain. Multiply this by all the billions of grains in an emulsion. These clumps are BLACK because they consist of metallic silver. So yes they *could* theoretically block light from reaching an underlying sensitivity speck. This MIGHT explain that shoulder that gives the extended exposure latitude of film... I DON'T KNOW, but don't discount it with some smart comment and no thought.

 

Rishi

[vijay_nebhrajani]

And Mauro, what you are talking about (non-linear capture that extends dynamic range) is actually called companding. See the relevant <a href="http://en.wikipedia.org/wiki/Companding">wikipedia article on companding</a>.

<p>

Companding needs a variable gain amplifier in the path - which amplifies small signals a lot, and large signals less. Film don't have no variable amp. If it did, you couldn't have nice geometric apertures and shutter speeds (geometric as in geometric progressions).

[rishij]

What I meant to say at the beginning of my last post was: Re-read my post -- I was asking for explanations... NOT ATTACKING YOU.

 

Forgot to add that last bit in CAPS.

[rishij]

<i>"And Mauro, what you are talking about (non-linear capture that extends dynamic range) is actually called companding. See the relevant wikipedia article on companding."</i>

<p>

<b>YES!!</b> That's what I was talking about! Sorry I didn't know the technical term back then. Now do you retract your comment that linearity (or non-linearity) of capture is absolutely unrelated to the range of intensities recordable??

<p>

Sure a digital sensor would need a variable gain amplifier in the path that amplifies larger signals less -- duh, that was already stated above that that's what'd be needed to extend the exposure latitude of digital sensors. Canon's trying their own implementation in 'highlight tone priority', but I believe it only tries to simulate the effects of a variable gain amplifier.

<p>

The other way to achieve it, <i>in film</i>, would be to employ exactly the technique that I mentioned before -- clumps of silver increasing local density at sensitivity specks, blocking photon penetration to sites directly below. Or negative charge buildup at sulfide electron traps, though, in my opinion, that effect would be small.

<p>

Rishi

[mauro_franic]

Vijay, "Companding needs a variable gain amplifier in the path - which amplifies small signals a lot, and large signals less. Film don't have no variable amp. If it did, you couldn't have nice geometric apertures and shutter speeds (geometric as in geometric progressions)"

 

Vijay, you are getting confused to a more simple level now. Yes you can have geometric apertures (each lets twice/half the amount of light through with every single stop) - THAT DOESN'T MEAN THAT WHEN THEY IMPACT THE FILM WITH THE SAME PROGRESSION. i.e., the negative does not get twice as dense when when you go from f11 to f8. It gets denser but not twice.

 

Please read the publication I gave you the link for.

[bernardwest]

<i>Canon's trying their own implementation in 'highlight tone priority', but I believe it only tries to simulate the effects of a variable gain amplifier.</i><p>

 

Rishi... last time I saw HTP beaten to death on a forum (LL), it was agreed that HTP was nothing more than underexposure by 1 stop, then boosting the shadow data. You can implement it manually by dialling in -1 EC and then applying a bit of "fill light" in LR/ACR.<p>

 

I am going to tentatively have a crack at this non-linear shoulder thing, but until I get home and check the references, I will leave it as a discussion point. Hopefully Rishi you have covered it in your reading and can confirm if my memory is serving me correctly. I seem to remember it stated somewhere that as more silver ions are converted to silver metal at sensitivity centres, the less sensitive those centres become. When I get home I'll try and find out if this is a correct recollection. Cheers.

[mauro_franic]

Top of page 5.

 

http://www.kodak.com/global/en/professional/support/techPubs/e4046/e4046.pdf

[mauro_franic]

Bernie, you are right, Canon's highlight priority is nothing more (so far) than underexposure with curves.

 

There is no debate there. To simulate film you would need a log gain AT THE PIXEL LEVEL.

[vijay_nebhrajani]

OK Rishi - your tone was quite, umm shall we say - hostile. If that wasn't your intention, then I misread it and

apologize for that. I wasn't being arrogant or trying to make fun of you. I was pointing out several realities

that don't quite jive with the negative film/exposure latitude theory being floated on this thread.

 

I wasn't specifically pointing out at you that you didn't know about dynamic range. It was a general comment -

dynamic range is a ratio.

 

Now you deflect to exposure latitude. Let me take a stab at defining that. Let's say a scene has a dynamic range

of 6 stops. Let's say your film has a dynamic range of 10 stops. The difference is the exposure latitude. You can

err by 4 stops (2 stops in each direction), and will be able to recover a perfectly fine image. This is because

you can place the 6 stops (zones) of the scene in any part of a 10 stop available range.

 

On the other hand, if the scene has a 15 stop range, and your system has 13 stops of dynamic range, then your

latitude is negative - no matter what you do, you will lose detail.

 

Latitude is not a characteristic of a system; it is just what happens when a signal (light) has less dynamic

range than the channel (film in this case). Talking about latitude as if it were a system characteristic (i.e., a

property of film) is an exercise in meaninglessness.

 

Now for getting back half stop from the curved portions of the Hurter Driffield curve - look at the curves for,

say Ektar 100. How much is the length of the toe before the density hits Dmin? Barely a third of a stop. This is

all you could theoretically straighten out. The rest is already linear - the linear part of the sensitometric

curve. You need a reference for something as straightforward as this?

 

And lastly, if the accumulated silver blocks light to a significant degree, then it would make the response of

film non-linear. As we know from the Hurter Driffield curve you pointed out, that is not the case. The already

formed latent image can't significantly affect further formation of the latent image because that would make the

response non-linear, which it is not.

[vijay_nebhrajani]

<i>Mauro: "Vijay, you are getting confused to a more simple level now. Yes you can have geometric apertures (each

lets twice/half the amount of light through with every single stop) - THAT DOESN'T MEAN THAT WHEN THEY IMPACT THE

FILM WITH THE SAME PROGRESSION. i.e., the negative does not get twice as dense when when you go from f11 to f8.

It gets denser but not twice. "</i>

<p>

You miss the point that if the negative gets (say) 1.5 times as dense going from f/2.8 to f/2, it also gets 1.5

times as dense going from f/11 to f/8.

<p>

Companding would require that the negative gets (say) 1.8 times as dense going from f/11 to f/8 but 1.2 times

going from f/2.8 to f/2 (more light, less gain).

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Sorry Mauro, the former is not a variable gain amp - it's just an "amp" with gain of 1.5. The latter is; but you

know as well as I do that film does not behave like that.