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Author Topic: lack of dynamic range  (Read 3281 times)
woodsman
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« on: April 16, 2007, 07:21:12 PM »
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I've been battling with this for ages, but not getting anywhere...

Over the past few years I've had a succession of Minolta, Konica/Minolta then Sony cameras (currently using an A2 and an A100), and have been very happy with them apart from the lack of dynamic range (as I call it).  I take a lot of pictures in woodlands, where the light range can be extreme.  I have always ended up with a series of images where either the sky is over-exposed or the shadows are under-exposed; I cannot, no matter how many fiddles I try, get the full range.  Even processing in Photoshop (although I possibly haven't explored all its possibilities) doesn't produce good images.

Is this to be expected?  Am I asking too much of my camera?
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BernardLanguillier
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« Reply #1 on: April 16, 2007, 07:30:15 PM »
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Well, there are clearly situations in which the current best offerings in terms of DR (the Canon 5D in 35 mm or better yet MFDB) will not be able to hold detail in both highlights and shadows. The situation you describe could be one of these.

The Sony A100 isn't supposed to be significantly worse/better than its 6MP competitors in this area, and you might simply be running into technological limitations. Those limitations were by the way also present in the film days, and slides would probably be even more difficult to use in these high contrast situations.

Here are however some considerations:

- it is important to distinguish lack of DR and contrasty default curve. I know that my d2x has a pretty contrasty default curve that makes it look like the DR is limited. The shadows are however in fact amazingly clean and it is fairly easy to expand that default behaviour so as to get a much softer rendition. You A100 could be similar,

- Shooting RAW helps getting all the available DR out of a camera body,

- Some RAW converters are better than others at extracting all the available DR. Adobe lightroom makes this rather easy nowadays,

- When the RAW converter cannot do wonders at once, it sometimes help to convert the image twice. Once for the highlghts, once for the shadows, and then to layer these 2 images in PS and manage contrast using masks,

- When that is not enough, you can do what is called exposure stacking. You take several images with different exposures, and the post-process them so as to increase the apparent DR. You can do this manually by overlaying/masking in PS, or use one of the available High Dynamic Range software options available on the market. PS CS2/CS3 has a function supposed to do that, although I am personnally not convinced by most of the results I see. I perfer to used to old manual technique.

For these multi-exposures to work, they need to be taken from exactly the same location, which makes the use of a tripod mandatory for perfect results.

Hope that it helps.

Cheers,
Bernard
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A few images online here!
woodsman
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« Reply #2 on: April 16, 2007, 07:44:16 PM »
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Well, there are clearly situations in which the current best offerings in terms of DR (the Canon 5D in 35 mm or better yet MFDB) will not be able to hold detail in both highlights and shadows. The situation you describe could be one of these.

The Sony A100 isn't supposed to be significantly worse/better than its 6MP competitors in this area, and you might simply be running into technological limitations. Those limitations were by the way also present in the film days, and slides would probably be even more difficult to use in these high contrast situations.

Here are however some considerations:

- it is important to distinguish lack of DR and contrasty default curve. I know that my d2x has a pretty contrasty default curve that makes it look like the DR is limited. The shadows are however in fact amazingly clean and it is fairly easy to expand that default behaviour so as to get a much softer rendition. You A100 could be similar,

- Shooting RAW helps getting all the available DR out of a camera body,

- Some RAW converters are better than others at extracting all the available DR. Adobe lightroom makes this rather easy nowadays,

- When the RAW converter cannot do wonders at once, it sometimes help to convert the image twice. Once for the highlghts, once for the shadows, and then to layer these 2 images in PS and manage contrast using masks,

- When that is not enough, you can do what is called exposure stacking. You take several images with different exposures, and the post-process them so as to increase the apparent DR. You can do this manually by overlaying/masking in PS, or use one of the available High Dynamic Range software options available on the market. PS CS2/CS3 has a function supposed to do that, although I am personnally not convinced by most of the results I see. I perfer to used to old manual technique.

For these multi-exposures to work, they need to be taken from exactly the same location, which makes the use of a tripod mandatory for perfect results.

Hope that it helps.

Cheers,
Bernard
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Thanks Bernard. You've raised some techniques that wasn't aware of.  I shall try your last two tricks and see what happens. Thanks again.
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francois
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« Reply #3 on: April 17, 2007, 02:39:55 AM »
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You may want to read Michael's Digital Blending tutorial (here) and Highlight Recovery article (PDF: here). It will give you valuable info about stacking RAW files (either 2 or more different RAW captures or same RAW file with different treatment) to get expanded DR.
« Last Edit: April 17, 2007, 02:41:23 AM by francois » Logged

Francois
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« Reply #4 on: April 17, 2007, 06:36:39 AM »
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I take a lot of pictures in woodlands, where the light range can be extreme. I have always ended up with a series of images where either the sky is over-exposed or the shadows are under-exposed; I cannot, no matter how many fiddles I try, get the full range.
When you are inside a forest and a beam of sunlight intrudes you have one of the greatest exposure challenges I know of. One might almost think of the sunlight as representing specular glare. Even the somewhat less extreme case of trying to expose for both sky and a forest interior can easily push film or sensor to the limit.

And you don't even need to leave the house to match this degree of exposure latitude. During the daytime simply take a photo indoors that includes the interior of a room plus a view through a window. A room lit only by a single smallish window (perhaps a bathroom?) is ideal. If you happen to have a spot meter on or off camera, use it to meter the scene outside through the window and the wall of the room about a foot to the left or right of the window. Your eyes+brain easily handle both brightness levels in the same scene, but few cameras can, since we're easily talking 10 stops here, if memory serves.

Even if you do have a sensor or film stock with that kind of latitude, exposing so that the scene through the window is not entirely blown results in so little exposure to the interior that the level of noise or film graininess becomes highly problematic.

The upshot is: no, neither your cameras nor your exposure technique is lacking; and yes, some form of multiple exposure is required.
« Last Edit: April 17, 2007, 07:27:44 AM by Dale Cotton » Logged
woodsman
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« Reply #5 on: April 19, 2007, 05:03:39 PM »
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many thanks for all your comments and suggestions.  I've followed the links given by francois and found them very, very helpful, and have made some much improved versions of some of my favourite compositions which were previously really too poor for words! It would be good to take a tripod out, but practicalities really exclude this most of the time, so the software options that blend different versions of the RAW images is my best option.  Many thanks again.
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francois
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« Reply #6 on: April 20, 2007, 02:49:27 AM »
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many thanks for all your comments and suggestions. I've followed the links given by francois and found them very, very helpful, and have made some much improved versions of some of my favourite compositions which were previously really too poor for words! It would be good to take a tripod out, but practicalities really exclude this most of the time, so the software options that blend different versions of the RAW images is my best option. Many thanks again.
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You may also try Tim Gray's [a href=\"http://luminous-landscape.com/forum/index.php?showtopic=15795&view=findpost&p=110697]technique[/url] to blend the same RAW file:

Try this simple technique.

Process the original RAW 2 times, adjusting the exposure - one over exposed to bring out the shadows and one underexposed to reduce highlight clipping.

Open the under exposed image and copy the over exposed image on top.

With the top layer selected (the over exposed one), hit ctrl alt ~ this selects the brightest pixels of the over exposed layer, then Delete. (after ctrl alt ~ you could hit the mask icon and go from there).


It can speed up blending and give good results.
Good luck!
« Last Edit: April 20, 2007, 02:50:10 AM by francois » Logged

Francois
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« Reply #7 on: April 20, 2007, 03:10:16 AM »
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You may also try Tim Gray's technique to blend the same RAW file:

Try this simple technique.

Process the original RAW 2 times, adjusting the exposure - one over exposed to bring out the shadows and one underexposed to reduce highlight clipping.

Open the under exposed image and copy the over exposed image on top.

With the top layer selected (the over exposed one), hit ctrl alt ~ this selects the brightest pixels of the over exposed layer, then Delete. (after ctrl alt ~ you could hit the mask icon and go from there).


It can speed up blending and give good results.
Good luck!
[a href=\"index.php?act=findpost&pid=113365\"][{POST_SNAPBACK}][/a]

Any idea what the equivalent keystroke is on a Mac?

Jeremy
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francois
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« Reply #8 on: April 20, 2007, 03:47:49 AM »
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Any idea what the equivalent keystroke is on a Mac?

Jeremy
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it's CMD (Apple key) + Option + ~

You can also do it by selecting the Channels palette and click in the RGB channel while holding the Apple key (CMD).
« Last Edit: April 20, 2007, 03:48:35 AM by francois » Logged

Francois
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