An idea for cutting down levels of grain

[Laurent Andrieux]

there is opportunity for a small ammount of correction, but maybe only a stop of underexposure and a half stop of overexposure

 

It all depends on the subject's contrast...

[Filip Plesha]

As to come back to Daniel's first post, I was wondering if the fact that reversal is considered like "zeo latitude" is not only due to the fact that, originally, reversal is designed to be projected after processing, and since there is no printing, there is no possibility for correcting the original...

 

I wonder if this approach of "zero latitude" is not linked to this and not to the reversal stock caracteristics. I read somewhere that when you duplicate or print an intermediate from a reversal, both giving the ability of correcting the exposure, then you get a huge latitude with it...

<{POST_SNAPBACK}>

 

 

It's not just about reversal film. Any image digital or analog (video tape formats, digital photographs (exported, not raw), printed pictures, chromes, film prints) that can be viewed without any corrections basicly has "zero latitude".

It means that there is no information beyond the range that you see with your eyes.

 

When you look at a paper print of a photograph, the black appears as black

and white as white. You can't have whiter than white on paper.

So every shade of color on the paper is intended for you to see with your eyes

as it is.

 

Systems like negative film, or high dynamic range electornic imaging record

more ranges of brightness that you need for viewing, so you have a choice in

post production. Negative film, or HDR digital images are not ment for viewing,

they need special treatment (extraction of a portion of the dynamic range)

to be viewed.

 

Any image material that is intended for direct viewing can not have any

latitude in theory becuase black is intended to be black and white is intended to be white, there is no headroom and any elementary manipulation will result

in loss of pure black or pure white levels. Thatis zero latitude.

 

Now of course in practice you CAN manipulate zero latitude images, but

you have to cheat.

For example, if you want a brighter image, you can use curves to boost the midrange without affecting the blacks and highlights.

Or you can compensate for the loss of black with boosing contrast.

So you can say that you can distort the range so that it looks brighter or darker,

but you are not bringing any new information into the image.

 

On the other hand, with HDR images or negative film, you can choose your portion of the full dynamic range with simple movement of your white and black points

up or down. That the curve is untouched and stays linear, there no artefacts, becuase everything is done "naturaly" without having to force the curve into being something it is not, and by moving your white and black points up or down, you

introduce NEW information into the print/digital image that wasn't there in the final image with previous setting of printer/software

 

So with zero latitude images you can distort the curve and make an illusion

that you were printing up/down the image the regular way, but you are not doing that, you are just faking it to a certain point (until you start getting artefacts),

and there is no real new information introduced.

With HDR images, you can "print up/down" the image the real way (by moving

the limits of your printing range), there is no interpolation, no distortion, no faking.

That is what latitude is all about.

 

 

And of course, as David mentioned, due to the "definite" (it is made as a finished image) nature of reversal image, there can not be any more additional information than that you see when it is projected.

Pure white is transperent base with no color, how can you store additional highlights that are supose to be whiter than projector lamp seen through the transperent base? Impossible.

The brightest part of the transperecy will always be seen as the brightest spot on the screen. This is why it is said that reversal has zero latitude.

[Filip Plesha]

I asked this question in a still photography class once, and I remember there is opportunity for a small ammount of correction, but maybe only a stop of underexposure and a half stop of overexposure.  This is with something like 7250.  With the 100D reversal film that's out, there is probably even less latitude than that.  With Kodachrome 40A, there's almost no latitude at all.  You'd be lucky to correct 1/3 of a stop in either direction.

 

Regards.

~Karl Borowski

<{POST_SNAPBACK}>

 

Like I said, this is not real latitude, it is more of a "tolarance for cheating and getting away with it".

As soon as you try to print down reversal in copying, you loose the power of your white, and it apperas as gray on the copy.

The only way to do it is in electronic manipulation, there you can make it appear as if you printed down without loosing highlights.