Ad
Ad
Ad
Pages: [1] 2 3 ... 10 »   Bottom of Page
Print
Author Topic: interesting article  (Read 62790 times)
sgwrx
Full Member
***
Offline Offline

Posts: 158


« on: April 05, 2006, 03:37:18 PM »
ReplyReply

http://www.rags-int-inc.com/PhotoTechStuff/

the one i'm referring to is called "Tones n Zones"
Logged
61Dynamic
Sr. Member
****
Offline Offline

Posts: 1442


WWW
« Reply #1 on: April 05, 2006, 10:58:52 PM »
ReplyReply

Some interesting information in the article. I didn't get a chance to give it a full read so pardon me if I missed something. If I have time latter, I'll read it in full and respond more if needed.

Quote
The most serious misconception is that because of the computer’s binary ordering...
He is misinterpreting (or reacting to someone who misinterpreted) the purpose of that chart. It is not representing anything that results from binary ordering. The chart, which I recognize from Michael's Expose to the Right and Raw file articles (I've also used it in my Bit-Depth article), describes the linear nature of how camera sensors capture data. His discussion seems to evolve around a gamma 2.2 encoded file which I didn't see anything to object to.
« Last Edit: April 05, 2006, 10:59:26 PM by 61Dynamic » Logged
Tim Gray
Sr. Member
****
Offline Offline

Posts: 2002



WWW
« Reply #2 on: April 06, 2006, 09:24:08 AM »
ReplyReply

Quote from the article:

"Over exposure will clip tonal details quickly.   Under exposure also distorts tonal values, but it retains shadow detail longer and can be recovered easier.   This should not be news to any digital photographer. "

So he's proposing an "expose to the left" strategy?
Logged
jliechty
Full Member
***
Offline Offline

Posts: 113


« Reply #3 on: April 06, 2006, 09:54:12 AM »
ReplyReply

I'm marking this for reading later, but if indeed he is proposing an expose-to-the-left priority of exposure, then I'm going to have to respectfully disagree based on my practical experience. Exposing to the left and then pulling up in RAW conversion only increases noise and posterization, while exposing normally (or better yet in most cases, to the right) does not make these issues more acute.
Logged
61Dynamic
Sr. Member
****
Offline Offline

Posts: 1442


WWW
« Reply #4 on: April 06, 2006, 10:33:02 AM »
ReplyReply

He's not proposing expose to the left, but expose for midtones.
Logged
Graeme Nattress
Sr. Member
****
Offline Offline

Posts: 582



WWW
« Reply #5 on: April 06, 2006, 03:43:16 PM »
ReplyReply

It's an interesting, but difficult to follow article, where the conclusion doesn't seem to quite follow from the body of the argument. Gamma is always an interesting subject as it usually performs the dual purpose of perceptually encoding a higher dynamic range into a lower number of bits (ie 12bit sensor to 8bit data) and being the inverse characteristic to the traditional CRT monitor.

Graeme
Logged

www.nattress.com - Plugins for Final Cut Pro and Color
www.red.com - Digital Cinema Cameras
sgwrx
Full Member
***
Offline Offline

Posts: 158


« Reply #6 on: April 06, 2006, 04:58:25 PM »
ReplyReply

i've re-read "expose to the right" and the article i've posted, i'm still working this all out.

but one question, "expose to the right" seems to be taken within context of signal to noise ratio. would the following be an accurate application / example of "expose to the right":

one takes a photograph of a black leather couch against a medium gray wall.

if one exposes so that the black couch appears black, the couch would contain noise.

if one exposed to the right, making the black couch appear more towards white or middle gray, the couch would contain much less noise.

finally, in post processing one would adjust the raw image so that the shifted-towards-white/gray couch appeared more black.

the resulting image would contain much less noise than exposing the couch according to an in-camera meter's suggestion.
« Last Edit: April 06, 2006, 05:00:28 PM by sgwrx » Logged
digitaldog
Sr. Member
****
Offline Offline

Posts: 9011



WWW
« Reply #7 on: April 06, 2006, 07:32:59 PM »
ReplyReply

Quote
i've re-read "expose to the right" and the article i've posted, i'm still working this all out.

but one question, "expose to the right" seems to be taken within context of signal to noise ratio. would the following be an accurate application / example of "expose to the right":

one takes a photograph of a black leather couch against a medium gray wall.

if one exposes so that the black couch appears black, the couch would contain noise.

if one exposed to the right, making the black couch appear more towards white or middle gray, the couch would contain much less noise.

finally, in post processing one would adjust the raw image so that the shifted-towards-white/gray couch appeared more black.

the resulting image would contain much less noise than exposing the couch according to an in-camera meter's suggestion.
[a href=\"index.php?act=findpost&pid=62039\"][{POST_SNAPBACK}][/a]

I think you've summed it up well.

Expose to the right isn't about over exposing (duh), it's about exposing for a linear encoded file. That's kind of unique with RAW (everything else is gamma corrected). So ensuring you're not blowing out highlights and placing as much good data within that linear scale is what you want to try to accomplish. Film (the old stuff we're used to) wasn't linear encoded (remember those good old H&D curves?).
Logged

Andrew Rodney
Author “Color Management for Photographers”
http://digitaldog.net/
Chris_T
Sr. Member
****
Offline Offline

Posts: 541


« Reply #8 on: April 10, 2006, 07:20:16 AM »
ReplyReply

Quote
I think you've summed it up well.

Expose to the right isn't about over exposing (duh), it's about exposing for a linear encoded file. That's kind of unique with RAW (everything else is gamma corrected). So ensuring you're not blowing out highlights and placing as much good data within that linear scale is what you want to try to accomplish. Film (the old stuff we're used to) wasn't linear encoded (remember those good old H&D curves?).
[a href=\"index.php?act=findpost&pid=62054\"][{POST_SNAPBACK}][/a]

For a digital camera that only supports jpeg and not RAW, can you clarify the following:

- can this "expose to the right" technigue still be used?

- can the RAW conversion sw and methods (e.g. merging to expand dynamic range, etc.) be used on jpegs?

Thanks.
Logged
digitaldog
Sr. Member
****
Offline Offline

Posts: 9011



WWW
« Reply #9 on: April 10, 2006, 10:11:18 AM »
ReplyReply

Quote
For a digital camera that only supports jpeg and not RAW, can you clarify the following:

- can this "expose to the right" technigue still be used?

- can the RAW conversion sw and methods (e.g. merging to expand dynamic range, etc.) be used on jpegs?

Thanks.
[a href=\"index.php?act=findpost&pid=62272\"][{POST_SNAPBACK}][/a]

No, the expose to the right is specifically for linear encoded data (RAW). A JPEG is an existing rendered 8-bit file. You get what you get. That's the beauty of RAW.
Logged

Andrew Rodney
Author “Color Management for Photographers”
http://digitaldog.net/
BJL
Sr. Member
****
Offline Offline

Posts: 5124


« Reply #10 on: April 10, 2006, 12:52:05 PM »
ReplyReply

Quote
For a digital camera that only supports jpeg and not RAW, can you clarify the following:

- can this "expose to the right" technigue still be used?

- can the RAW conversion sw and methods (e.g. merging to expand dynamic range, etc.) be used on jpegs?

Thanks.
[a href=\"index.php?act=findpost&pid=62272\"][{POST_SNAPBACK}][/a]
"Expose to the right" can still be used; I was doing it this weekend in sand-dunes. Basically, if you check the histogram and a substantial part at the right is flat zero, and a longer exposure time is acceptable, then you try again with increased exposure (+ compensation?) to improve shadow handling. You might then need to do some post-processing to bring tones down.

I believe that merging multiple frames to expand dynamic range is also possible; there is no fundamental reason why that would not be possible with JPEG.
Logged
DiaAzul
Sr. Member
****
Offline Offline

Posts: 777



WWW
« Reply #11 on: April 10, 2006, 01:21:52 PM »
ReplyReply

Quote
I believe that merging multiple frames to expand dynamic range is also possible; there is no fundamental reason why that would not be possible with JPEG.
[a href=\"index.php?act=findpost&pid=62296\"][{POST_SNAPBACK}][/a]

There is a great chunk of high dynamic range software that only works with JPEG files - I think even CS2 does some conversion on the RAW files, whether that is to JPEG or not I can't remember. Prior to merging successive frames the software needs to convert the  JPEG data gamma corrected and post application of tone curve to linear data (a kind of 'unbending' the data). RAW, linear, JPEG, TIFF it is possible to use all types of files as input for high dynamic range images.
Logged

David Plummer    http://photo.tanzo.org/
Schewe
Sr. Member
****
Offline Offline

Posts: 5469


WWW
« Reply #12 on: April 13, 2006, 04:54:52 PM »
ReplyReply

Quote
http://www.rags-int-inc.com/PhotoTechStuff/

the one i'm referring to is called "Tones n Zones"
[a href=\"index.php?act=findpost&pid=61937\"][{POST_SNAPBACK}][/a]



Rags Gardner unfortunately likes to take an engineer's background and apply it to something he really doesn't understand-photographic exposure. He still thinks that digital should be "exposed for the mid-tones" ala film and the "old Zone System".

Let's see...on one hand we have Thomas Knoll, Bruce Fraser, Michael Reichmann. On the other side is Rags Gardner-who do you believe? I think I'll go with Thomas...in my experience he knows this stuff inside and out from the standpoint of digital sensors.

Rags writes: "So, let’s start with the fact that an image can be divided into lighting zones, as taught by Ansel Adams."

Well, that's where his whole argument falls down. You can't get to the zones until AFTER you apply a tone curve and that's where the distribution of tones from a linear capture gets turned into a gamma encoded image. Ever see a linear capture processed for linear gamma? Looks really dark and under exposed. It bares no relationship to a standard gamma encoded image whether digital or film.

Rags wrote this, uh, piece of uh, whatever in direct response to an online dispute with Bruce Fraser at the Adobe Camera Raw forums...it looks authoritative, but it's fundamentally flawed. Digital capture is recorded in linear manner and it's not until the linear image is demosaiced and tone curved that it represents an image one can see and use. Rags wants to try to convince people to meter and expose for zone V which worked with B&W film but for digital capture you should meter to just maintain textural highlight detail-much more like zone IX if anything.
« Last Edit: April 13, 2006, 04:57:29 PM by Schewe » Logged
Graeme Nattress
Sr. Member
****
Offline Offline

Posts: 582



WWW
« Reply #13 on: April 13, 2006, 05:00:19 PM »
ReplyReply

It is correct to expose for highlight and ensure they don't clip, but don't waste bits either. You're right that linear gamma images look dark and underexposed, and that they need both a gamma correction and a s-curve to look correct.

Graeme
Logged

www.nattress.com - Plugins for Final Cut Pro and Color
www.red.com - Digital Cinema Cameras
digitaldog
Sr. Member
****
Offline Offline

Posts: 9011



WWW
« Reply #14 on: April 13, 2006, 05:50:31 PM »
ReplyReply

Quote
It is correct to expose for highlight and ensure they don't clip, but don't waste bits either. You're right that linear gamma images look dark and underexposed, and that they need both a gamma correction and a s-curve to look correct.

Graeme
[a href=\"index.php?act=findpost&pid=62501\"][{POST_SNAPBACK}][/a]

The don't look dark when you assign a profile for that capture. But the Histogram looks all pushed to one side due to the gamma encoding (which after a proper conversion to a working space levels out). I have linear encoded RGB files that look dark and ugly only up to the point I assign the proper profile, then they look just fine.
Logged

Andrew Rodney
Author “Color Management for Photographers”
http://digitaldog.net/
Graeme Nattress
Sr. Member
****
Offline Offline

Posts: 582



WWW
« Reply #15 on: April 13, 2006, 06:58:11 PM »
ReplyReply

Quote
The don't look dark when you assign a profile for that capture. But the Histogram looks all pushed to one side due to the gamma encoding (which after a proper conversion to a working space levels out). I have linear encoded RGB files that look dark and ugly only up to the point I assign the proper profile, then they look just fine.

But what is that assigning of a profile doing, image processing-wise?

Graeme
Logged

www.nattress.com - Plugins for Final Cut Pro and Color
www.red.com - Digital Cinema Cameras
digitaldog
Sr. Member
****
Offline Offline

Posts: 9011



WWW
« Reply #16 on: April 13, 2006, 07:49:02 PM »
ReplyReply

Quote
But what is that assigning of a profile doing, image processing-wise?

Graeme
[a href=\"index.php?act=findpost&pid=62512\"][{POST_SNAPBACK}][/a]

It defines the scale of the numbers so Photoshop properly previews the numbers. That's all a profile does (define numbers within a scale of human vision).
Logged

Andrew Rodney
Author “Color Management for Photographers”
http://digitaldog.net/
bjanes
Sr. Member
****
Offline Offline

Posts: 2785



« Reply #17 on: April 13, 2006, 09:24:52 PM »
ReplyReply

Quote
Rags Gardner unfortunately likes to take an engineer's background and apply it to something he really doesn't understand-photographic exposure. He still thinks that digital should be "exposed for the mid-tones" ala film and the "old Zone System".

Rags writes: "So, let’s start with the fact that an image can be divided into lighting zones, as taught by Ansel Adams."

Well, that's where his whole argument falls down. You can't get to the zones until AFTER you apply a tone curve and that's where the distribution of tones from a linear capture gets turned into a gamma encoded image. Ever see a linear capture processed for linear gamma? Looks really dark and under exposed. It bares no relationship to a standard gamma encoded image whether digital or film.

If anything, the zones are easier to work with in linear since each zone is exactly twice the value of the preceeding. Each stop of extra exposure doubles the pixel value. The relationships are well demonstrated on Norman Koren's site:

http://www.normankoren.com/digital_tonality.html

As Mr. Rodney noted, a gamma one image looks just fine in Photoshop if the proper profile is attached, but that is true for other spaces as well.
Logged
Schewe
Sr. Member
****
Offline Offline

Posts: 5469


WWW
« Reply #18 on: April 13, 2006, 09:57:50 PM »
ReplyReply

Quote
If anything, the zones are easier to work with in linear since each zone is exactly twice the value of the preceeding.
[a href=\"index.php?act=findpost&pid=62523\"][{POST_SNAPBACK}][/a]

If you want to work in a linear space and make a custom Photoshop working space with a gamma 1.0, then yes. But the big point of failure with Rag's 18% midtone approach is in linear space, a middle grey-the target Rag's says to shoot for is about level 50 in an 8 bit linear file. Way too low to do any kind of "normal" tone curve and it's pretty far south of optimal in terms of midtone. And if you examine the relative levels consentration of a gamma 1.0 image there is WAY too many levels packed into the brightest bits (the expose to the right concept) and a gamma 1.0 image in 8 bit/channel would be extremely prone to breaking.

The raw image capture is in linear and has far more bits (levels) to deal with in the highlights. The shadows far less bits. Therefore it makes far more sense to expose for the textural highlights and make use of all those bits. It's far easier and produces much better signal to noise to keep the midtone up the scale not down the scale. You can easily make things darker without adding noise than the other way around.
Logged
Ray
Sr. Member
****
Offline Offline

Posts: 8880


« Reply #19 on: April 13, 2006, 11:35:52 PM »
ReplyReply

A big breakthrough in dynamic range is long overdue. The current linear capture system provides far too many levels for the brighter parts of the image and far too few levels for the darker tones. If the scene is of relatively low dynamic range, consisting mainly of midtones, there's no great need to expose to the right. Correct exposure for the mid tones will suffice. If the DR of the scene is wide, as many landscape shots are which include sky or sunlit areas, then exposing to the right is pretty essential for noise-free shadow detail.

Since I'm not an engineer, I find it difficult to appreciate the difficulties involved in devising a capture system which compresses the DR. That is, one which redistributes the levels through a process of selective augmentation of low level signals.

We already have an example of excellent noise reduction with Canon DSLRs at high ISO. Take two shots using the same exposure, but one at ISO 100 and the other at ISO 1600, then compare the shadows. The ISO 1600 shot will likely have much better shadow detail, yet those shadows (on the sensor) in both shots have received the same amount of light. It seems that amplification of the analog signal prior to digitisation allows for dramatic noise reduction. Of course, if the exposure at ISO 100 was a full exposure to the right, then the same exposure at ISO 1600 would blow the highlights by 4 stops of overexposure.

But supposing there was a way of diminishing the intensity of those 4 stops, ie. the darker tones are augmented and the brighter tones are simultaneously diminished. We would then have a compression of dynamic range which, when unpacked, could be very wide indeed.

I'm reminded of developments in vinyl LP audio recording prior to the audio CD. The dynamic range of LP discs used to be typically around 50dB until a system called dbx was invented which compressed the signal at the recording stage, uncompressed it during playback producing a significant boost to DR which, as I recall, was around 80dB. However, CD audio gave us around 90dB and greater, so the dbx technology was too late.
Logged
Pages: [1] 2 3 ... 10 »   Top of Page
Print
Jump to:  

Ad
Ad
Ad