Luminous Landscape Forum
Equipment & Techniques => Digital Cameras & Shooting Techniques => Topic started by: OpticalMedia on July 21, 2006, 07:20:23 pm
-
I'm wonder if anyone can help put me in the spotlight. I am trying to establish the most effiecient technique I can use to get the best image quality out of my digital SLR while trying to cover the max possible dynamic range. However after studing all of michaels pages dedicated to this topic i am still confused. I Have a few questions in a specific order :
1. When would I use the expose to the right theory?
2. If i'm going to use this theory, is it not better rather to take multiple exposures and then digitally blend them?
3. What is the diffence btw the two methods?
4. Can they be used together ?
i'm sure with answers that will follow i'l have more questions.
Thank you in advance
-
Always keep your histogram as much to the right as possible withough clipping the highlights. This gives you as much postprocessing rooom as possible to manage the shadows.
If going as far right as possible still results in clipped shadows then you move into a blending mode by increasing the exposoure (time not f stop) by a half to full stop and take a second shot. Repeat until the shadows are no longer clipped.
ETTR gives you maximum latitude in processing a single shot but sometime the dynamic range can't be captured in a single shot, hence blending of 2 (or more) shots. Sometimes if you didn't bracket a scene with a _bit_ too much dynamic range you can still get a reasonable image by double processing the same raw shot and blending.
-
1. When would I use the expose to the right theory?
On every exposure you make. ETR mazimizes the Dynamic Range available from your imager.
2. If i'm going to use this theory, is it not better rather to take multiple exposures and then digitally blend them?
Not necessarily. Some subjects cannot accommodate multiple exposures. Sports, for example. Any situation with subject motion between exposures can't easily utilize blending procedures.
3. What is the diffence btw the two methods?
ETR is a way of maximizing the dynamic range available from a single exposure to an imaging system. Multiple exposure blending is a way of maximizing DR from a given photographic situation. By intentionally over and under exposing separate shots and combining the results, you can extract more information from a high contrast scene.
4. Can they be used together ?
Yes and no. Note that exposure blending requires the combination of both "under" and "over" exposed images. These may or may not fall within the ETR principle
i'm sure with answers that will follow i'l have more questions.
Thank you in advance
[a href=\"index.php?act=findpost&pid=71424\"][{POST_SNAPBACK}][/a]
-
sometimes you'll find yourself shooting a scene where the histogram shows as a big hump in the middle, nothing much down left and nothing much up right - like a bell curve. this is especially a time when you want to use ETTR.
sometimes there are scenes that contain one or two white objects like the hull of a sailboat. if it's pretty much the only thing that's pure white, and everything else in the scene is more or less mid-tone or darker, you can still use ETTR even though there might be some blowout in the hull. of course, if you want to retain detail like a small thing blue pinstripe, then it wouldn't be worth it.
-
I've seen plenty of images I've taken that are exposed to the left and they are superior to those I exposed to the right. This is because the exposure is the camera's best guess for the scene. It is many times fooled into over or underexposing and only your LCD can show you that. The histogram will not guide you because it will look like the exposure is dead on, and then be visually blown out on the LCD.
Also, if you expose to the right, you can lose color saturation that RAW processing will not recover. So this ideas in theory is correct because it helps the sensor capture more detail in the shadows, but in practice, it can play havoc with your images.
As an example, I shoot many dusk and night shots, and I almost never get a nice, accurate exposure reading from my 20D or nor now my 5D unless I use something like center weighted, aim for the most average brightness of the scene, and have a gradual light to dark transition in the scene--something like taking a picture of a boat and it's mast about 10 minutes after sunset. But then if I expose to the right, I lose color saturation, although I may save detail in the shadows.
But then again, due to inaccurate meter readings, I may be exposing to the right and not even know it. That being the case, what I do is bracket many shots in these situations. After all, you are shooting digital now. It cost nothing to shoot brackets. It does take more time though, so choose brackets logically, not willy nilly, or you will end up with 100s of images to look at. That eats hours, and hours, and h. . . . .
-
I've seen plenty of images I've taken that are exposed to the left and they are superior to those I exposed to the right. This is because the exposure is the camera's best guess for the scene. It is many times fooled into over or underexposing and only your LCD can show you that. The histogram will not guide you because it will look like the exposure is dead on, and then be visually blown out on the LCD.
Also, if you expose to the right, you can lose color saturation that RAW processing will not recover. So this ideas in theory is correct because it helps the sensor capture more detail in the shadows, but in practice, it can play havoc with your images.
ill end up with 100s of images to look at. That eats hours, and hours, and h. . . . .
[a href=\"index.php?act=findpost&pid=71456\"][{POST_SNAPBACK}][/a]
I think that the above cautions about color saturation are overblown. The sensors in most digital cameras are linear right up to the point of clipping. A few show some nonlinearity near the top. As long as you remain in the linear range and avoid clipping, there will be no loss of saturation with exposure to the right. When clipping occurs, there will be color shifts and loss of highlight detail. Often, it is the white highlights that blow first, and in this situation the green channel will blow first with daylight white balance, resulting in a magenta shift.
When exposing low key subjects to the right, the picture will appear too light, and a negative exposure compensation in the raw converter will be needed. Since digital capture is linear in all channels, no color shifts or changes in saturation will occur. However, the shadows in the image will have less noise because of the ETTR.
Bill
-
If going as far right as possible still results in clipped shadows[a href=\"index.php?act=findpost&pid=71432\"][{POST_SNAPBACK}][/a]
Eeek! That phrase "clipped shadows" sounds like nails on a blackboard to me. Shadows don't clip in camera captures; only in Levels and Curves tools in post-processing.
In capture, shadows get obscurred in noise, they don't get clipped. They're still there; just hard to see.
-
Always keep your histogram as much to the right as possible withough clipping the highlights. This gives you as much postprocessing rooom as possible to manage the shadows.
If going as far right as possible still results in clipped shadows then you move into a blending mode by increasing the exposoure (time not f stop) by a half to full stop and take a second shot. Repeat until the shadows are no longer clipped.
ETTR gives you maximum latitude in processing a single shot but sometime the dynamic range can't be captured in a single shot, hence blending of 2 (or more) shots. Sometimes if you didn't bracket a scene with a _bit_ too much dynamic range you can still get a reasonable image by double processing the same raw shot and blending.
[a href=\"index.php?act=findpost&pid=71432\"][{POST_SNAPBACK}][/a]
-
[attachment=885:attachment][attachment=886:attachment]
Always keep your histogram as much to the right as possible withough clipping the highlights. This gives you as much postprocessing rooom as possible to manage the shadows.
If going as far right as possible still results in clipped shadows then you move into a blending mode by increasing the exposoure (time not f stop) by a half to full stop and take a second shot. Repeat until the shadows are no longer clipped.
ETTR gives you maximum latitude in processing a single shot but sometime the dynamic range can't be captured in a single shot, hence blending of 2 (or more) shots. Sometimes if you didn't bracket a scene with a _bit_ too much dynamic range you can still get a reasonable image by double processing the same raw shot and blending.
[a href=\"index.php?act=findpost&pid=71432\"][{POST_SNAPBACK}][/a]
The "Understanding Digital Blending" tutorial has been the most helpful shortcut. I have been using it on single scanned negs, and even the attached digital camera photo. The process is brilliant. In many cases, especially with color negs, I don't need to make multiple exposures.
-
I think that the above cautions about color saturation are overblown. The sensors in most digital cameras are linear right up to the point of clipping. A few show some nonlinearity near the top. As long as you remain in the linear range and avoid clipping, there will be no loss of saturation with exposure to the right. When clipping occurs, there will be color shifts and loss of highlight detail. Often, it is the white highlights that blow first, and in this situation the green channel will blow first with daylight white balance, resulting in a magenta shift.
When exposing low key subjects to the right, the picture will appear too light, and a negative exposure compensation in the raw converter will be needed. Since digital capture is linear in all channels, no color shifts or changes in saturation will occur. However, the shadows in the image will have less noise because of the ETTR.
Bill
[a href=\"index.php?act=findpost&pid=71461\"][{POST_SNAPBACK}][/a]
That is inaccurate in my practical experience given my specific explanation. Your technical explanation seems true enough, but in practice, it is not that easy. First, your camera may not be giving you an accurate exposure. In my case shooting highly contrasted sunsets and night shots, sometimes exposing to the right would mean blowing the entire scene to white. Using the histogram, it looks like it's bunched up to the left side. When I get home, it's near perfect. The only way to get around this inaccurate in camera exposure is to use a light meter, measure the highlights and the darkest areas, and set your camera manually for the exposure inbetween those two measurements. And still, this may not produce the "best" exposure in high contrast situations. Even using the cameras spot meter for measuring distant areas of a scene sometimes does not work. What is true is that the more negative exposure you take, the less detail you will have in shadows, and more noise, as you point out.
If shadow details are more important than your mid tones and highlights, take that into consideration and expose as needed, and vice-versa. In many of my shots, the shadows will be black anyway, as in forground silhouettes against a brightly colored sunset, and the colors and highlights are critical. However, I have the advantage of taking left and right exposures because of the situation, so I do take advantage of that.
Also note that in some images, you don't want a human eye like contrast between your highlights and shadows. You want that film/digital contrast, from darker to lighter to pull the eye into the scene. I have a friend who blends all of his sunset shots and I've heard many say that they lack something that keeps them interested in the images, but they all say that the colors are very pretty and the details are all very nice. I think part of that is becsaue the entire image has very little contrast from the highlights to the shadows--everything is very detialed and visible. Best thing to do is bracket and see which ones appeal to you the most for the effect you want, and then composite if needed. Be aware of the technical aspects, that Bill points out, are pretty much fact--you will lose detail in the shadows the more underexposed you get. And you will lose highlights and color if you over expose too much. I do not think there is anyway for a human operating a camera to get the "perfect" exposure by simply exposing to the right. But that is my opinion and I will not try to support that assertion.
-
I do not think there is anyway for a human operating a camera to get the "perfect" exposure by simply exposing to the right. But that is my opinion and I will not try to support that assertion.
[a href=\"index.php?act=findpost&pid=78734\"][{POST_SNAPBACK}][/a]
Linear data benefits nothing from under-exposure, except to avoid clipping of highlights. Any problem due to high, non-clipped/saturated exposure is the fault of the RAW converter, or the parameters used.
Unfortunately, popular converters like ACR provide no way for the user to simply scale the exposure before the rest of the conversion. Loss of color saturation in highlights, other than from clipping, is from converter contrast reduction of what it assumes, incorrectly, to be specular highlights.
-
Linear data benefits nothing from under-exposure, except to avoid clipping of highlights. Any problem due to high, non-clipped/saturated exposure is the fault of the RAW converter, or the parameters used.
Unfortunately, popular converters like ACR provide no way for the user to simply scale the exposure before the rest of the conversion. Loss of color saturation in highlights, other than from clipping, is from converter contrast reduction of what it assumes, incorrectly, to be specular highlights.
[a href=\"index.php?act=findpost&pid=78783\"][{POST_SNAPBACK}][/a]
hehe. There's always more to the story than meets the eye. Thanks for that information.
-
Linear data benefits nothing from under-exposure, except to avoid clipping of highlights. Any problem due to high, non-clipped/saturated exposure is the fault of the RAW converter, or the parameters used.
Unfortunately, popular converters like ACR provide no way for the user to simply scale the exposure before the rest of the conversion. Loss of color saturation in highlights, other than from clipping, is from converter contrast reduction of what it assumes, incorrectly, to be specular highlights.
[a href=\"index.php?act=findpost&pid=78783\"][{POST_SNAPBACK}][/a]
OK, Your right, but how to easily recover saturation using ACR
-
OK, Your right, but how to easily recover saturation using ACR
[a href=\"index.php?act=findpost&pid=78876\"][{POST_SNAPBACK}][/a]
If the data did not record due to technological limitations, you can't. It's not there to begin with.
-
Sorry for the previous post, the word "loss" is missing which change all the meaning.
Linear data benefits nothing from under-exposure, except to avoid clipping of highlights. Any problem due to high, non-clipped/saturated exposure is the fault of the RAW converter, or the parameters used.
Unfortunately, popular converters like ACR provide no way for the user to simply scale the exposure before the rest of the conversion. Loss of color saturation in highlights, other than from clipping, is from converter contrast reduction of what it assumes, incorrectly, to be specular highlights.
[a href=\"index.php?act=findpost&pid=78783\"][{POST_SNAPBACK}][/a]
OK, but how to easily recover loss of saturation in the highlights without affecting saturation in the "mid and dark areas" with ACR
-
Sorry for the previous post, the word "loss" is missing which change all the meaning.
OK, but how to easily recover loss of saturation in the highlights without affecting saturation in the "mid and dark areas" with ACR
[a href=\"index.php?act=findpost&pid=79042\"][{POST_SNAPBACK}][/a]
My point is that there isn't an easy way. You have to play with the exposure, brightness, contrast and shadow sliders until you get what you want.
-
My point is that there isn't an easy way. You have to play with the exposure, brightness, contrast and shadow sliders until you get what you want.
[a href=\"index.php?act=findpost&pid=79072\"][{POST_SNAPBACK}][/a]
Yes, that's what I do.
But it can take a lot of time !
So, when I have a "shallow bell" histogram, I prefer not to expose to the right, but expose more in the center.
Results are often better !
The same problem can occur when you have to play with curves in order to decrease local contrast. You loose color saturation in that area.
And if you increase color saturation, you obtain too much color saturated dark areas !
-
I'm surprised no-one has mentioned auto exposure bracketing. If you really want to get the maximum dynamic range from a single exposure you are probably either going to have to mess around with an external light meter, or use the camera's histogram and highlight warning to assess the accuracy of the exposure, and then retake the shot if there's any doubt.
The histogram is based on a jpeg conversion and the jpeg conversion and the appearance of the histogram is influenced by the in-camera contrast settings. The RAW image, however, is not influenced by such settings.
I find the best approach is to do one's best to get an ETTR exposure but auto bracket +/- 2/3rds of a stop or so, or plus 1/3rd and minus 1 stop, whatever, as an insurance policy. If you are using 4gb flash cards there should be no problem.
I think the default setting is 'normal' exposure first and it's probably best to keep it that way because the normal exposure should be right most of the time. When trying to capture the moment within a very small time frame, the other 2 shots might not be ideal even though one is better exposed. On the other hand, it's not always possible to anticipate the best moment and there's still a possibility of getting both the perfect moment and the perfect exposure when using auto bracketing.
I can't see there's anything to lose by adopting the practice, except storage space.
-
I'm surprised no-one has mentioned auto exposure bracketing.
...
I can't see there's anything to lose by adopting the practice, except storage space.
[a href=\"index.php?act=findpost&pid=79197\"][{POST_SNAPBACK}][/a]
I'm a big fan of bracketing, but more often than not at least for marginal DR problems I find that the "well exposed" shot of the 3 gives me all the latitude I need, notwithstanding some flashing on the display or an "iffy" histogram.
Although hard disk storage isn't an issue, CF storage is, as is processing time - which includes downloading the redundant files, building the thumbnails and actually executing some kind of mental judgement process against the files all of which chews up "real" time.
IMHO the "best" solution would be a histogram/display that accurately reflects the DR captured by the RAW file.
-
Perhaps a bit "analog" but I still use my Cokin graduated neutral density filters!. when the dynamic range is to big for my 5D. IMHO its much better to create a 100%image on fore hand than to fidle your way in Photoshop with Digital blending.
Henk
-
The histogram is based on a jpeg conversion and the jpeg conversion and the appearance of the histogram is influenced by the in-camera contrast settings. The RAW image, however, is not influenced by such settings.
That's why I'm using "+1 color saturation" and minimum contrast in Jpeg settings, wich gives me more accurate histograms.
But it's not the perfect solution.
Still trying to know when to use luminance and RGB histogram for the more accurate results.
And discovered that Silkypix has a very good recovery feature for blown sky.
Want to compare it with Lightroom revovery to know which is the best.
Thierry
-
Although hard disk storage isn't an issue, CF storage is, as is processing time - which includes downloading the redundant files, building the thumbnails and actually executing some kind of mental judgement process against the files all of which chews up "real" time.
[a href=\"index.php?act=findpost&pid=79217\"][{POST_SNAPBACK}][/a]
Tim,
I can see that CF storage might be an issue (as well as write speed) if you are, for example, in the habit of taking multiple shots at the same exposure to capture the perfect moment in a football game. But for landscape shots, there should be no problem. At present I'm in Siem Reap photographing the temples at Angkor Wat. I have 2x4gb cards, 2x2gb cards and 2x1gb cards. Despite this place being a photographer's paradise (and I bracket everything), I rarely fill in 12 hours of shooting more than 2x4gb cards, with my 12.8mp 5D. Downloading to my laptop takes more time of course, but not my time. It's an automatic process.
Sorting and assessing the images does take more time, but Hey!, you don't want something for nothing, do you?
-
That's why I'm using "+1 color saturation" and minimum contrast in Jpeg settings, wich gives me more accurate histograms.
[a href=\"index.php?act=findpost&pid=79281\"][{POST_SNAPBACK}][/a]
+1 saturation is going to cause saturated colors to blow out in the review/histogram much faster than the RAW.
-
IMHO the "best" solution would be a histogram/display that accurately reflects the DR captured by the RAW file.
[a href=\"index.php?act=findpost&pid=79217\"][{POST_SNAPBACK}][/a]
That should have been on the very first digital to offer RAW output. I'm still waiting. These manufacturers play us for idiots.
-
That should have been on the very first digital to offer RAW output. I'm still waiting. These manufacturers play us for idiots.
[a href=\"index.php?act=findpost&pid=79308\"][{POST_SNAPBACK}][/a]
It's surprising how many people still shoot jpegs with their DSLR. If they want good sky detail, they'll simply underexpose the shot, which is not good for the shadows of course.
Whilst a RAW based histogram would be an improvement, it would not necessarily be a complete solution without a live preview, as you get with EVFs on P&S cameras. If you don't have a live histogram and you have the time to take a shot, study the RAW histogram and decide the exposure needs fine tuning and take another shot, then you're just as well off estimating exposure from the current rather inaccurate histogram and autobracketing. In fact, you're probably better off.
I'd rather have a shot that is over or underexposed by a small amount (with respect to ETR) that accidentally captured the best moment, than a perfectly exposed shot that missed the moment by a 5th of a second. If you're in aperture priority mode, there's also the possibility of misjudging the shutter speed required to freeze subject movement. The underexposed shot with its faster shutter speed might sometimes be the preferred one. Some of one's best shots can be unexpected, unanticipated or simply sheer accidents.
....and I didn't even mention the potential of composite images from the bracketed shots. Normally, blending different exposures to increase dynamic range requires the use of a tripod. However, mixing feathered selections can sometimes be done seamlessly without affecting the integrity of the scene. I'd be interested in any suggestions forum memebers might have as to the best methods of doing this. I've not yet come across a program that can successfully align hand-held shots for pixel sharp blending. There often seems to be a certain amount of rotation and twisting that takes place between hand-held bracketed shots within that full second or so time frame, especially when one is precariously perched on a slippery, moss-covered rock slab at a 45 degree angle to the ground.
-
My point is that there isn't an easy way. You have to play with the exposure, brightness, contrast and shadow sliders until you get what you want.
[a href=\"index.php?act=findpost&pid=79072\"][{POST_SNAPBACK}][/a]
Actually, it isn't all that hard, nor need it be very time-consuming at all, if the work-flow is designed logically and efficiently.
First I agree there is no loss of data unless an ETTR is clipped. Second, apparent over-exposure or apparent loss of saturation is easily compensated in PS because the information is there. Third, images with desirable data in the quartertones can become posterized without ETTR because there is not enough information to provide smooth tonal transitions so far to the left on the histogram. This is well explained in Michael's tutorial on the subject and verified from experience. It's correct most of the time.
ETTR exposures can look like crap in ACR, but I find the adjustments are usually quite straight-forward for a wide variety of images:
(1) If there is a bit of clipping, use Exposure to rescue some tonality, unless it is specular highlights which are often best left ignored;
(2) Use the linear version of Curves in ACR to bring out contrast by dragging the upper and lower end points of the curve to their corresponding end points of the histogram without clipping anything.
(3) If need be, go back to Adjust and tweak the brightness slider to improve the mid-tones.
(4) Check for CA, etc., then convert.
(5) If saturation still needs a boost, fix it in PS with an HSB Adjustment Layer or a Selective Color Adjustment Layer. The effect can be limited to a certain colour range, or using a layer mask limited to certain parts of the image.
Another way of improving the vibrancy of really flat images is before doing anything else, convert them to Lab and steepen the A and B curves insuring that they always pass through the center point of the matrix. But do it carefully - these are highly leveraged adjustments. The optimal way of doing this is to duplicate the background layer, add a Curves Adjustment layer with clipping path linked to the duplicated layer, adjust A and B, merge the two layers, then re-convert to RGB without flattening. This way you can adjust the strength of the new "Lab layer" in RGB mode by altering its opacity to taste. The reason for this procedure is that Adjustment Layers cannot survive mode changes between colour working spaces.
-
+1 saturation is going to cause saturated colors to blow out in the review/histogram much faster than the RAW.
[a href=\"index.php?act=findpost&pid=79307\"][{POST_SNAPBACK}][/a]
+1 saturation is to compensate for desaturation due to minimum contrast !!!
-
+1 saturation is to compensate for desaturation due to minimum contrast !!!
[a href=\"index.php?act=findpost&pid=79400\"][{POST_SNAPBACK}][/a]
General saturation affects all tonal ranges, though.
The saturation setting in the camera only affects the camera's conversion, or an external conversion, if it honors the file's defaults.
In-camera saturation settings have no effect on RAW capture. RAW capture always has the same saturation, at all levels except as affected by noise in the shadows, or hard-clipping or non-linearities in the highlights. The second-lowest ISO any camera can do is pretty much guaranteed not to have non-linear RAW highlights. It is usually only the lowest ISO that has non-linear highlights (if the camera has them at all).
-
Unfortunately, popular converters like ACR provide no way for the user to simply scale the exposure before the rest of the conversion.
John, doesn't the exposure slider in ACR linearly scale the exposure (in contrast to the brightness slider which applies a non-clipping curve)?
-
1. When would I use the expose to the right theory?
2. If i'm going to use this theory, is it not better rather to take multiple exposures and then digitally blend them?
3. What is the diffence btw the two methods?
4. Can they be used together ?
My two cents,
ETTR when taking a shot involving action (ie sports), otherwise bracket and digitaly blend. You can effectively remove all noise in a digital capture (even when appling a graduated neutral density filter digitally) by blending 5 to 7 exposures spaced 1 stop apart starting with the proper (non-clipping exposure) and overexposing. Larger exposure spacing and blending less exposures will result more noise, example below,
http://www.farrarfocus.com/ffdd/blog20060926.htm (http://www.farrarfocus.com/ffdd/blog20060926.htm)
I've found for landscapes, bracketing can faster then metering and checking for proper exposure or the right amount of ETTR.
-
I've seen plenty of images I've taken that are exposed to the left and they are superior to those I exposed to the right. This is because the exposure is the camera's best guess for the scene. It is many times fooled into over or underexposing and only your LCD can show you that. The histogram will not guide you because it will look like the exposure is dead on, and then be visually blown out on the LCD.
If you are seriously proposing that the appearance of the image on the little non-color-managed LCD on the back of the camera is a more reliable indicator of proper exposure than the histogram, you are sadly mistaken.
Also, if you expose to the right, you can lose color saturation that RAW processing will not recover. So this ideas in theory is correct because it helps the sensor capture more detail in the shadows, but in practice, it can play havoc with your images.
As an example, I shoot many dusk and night shots, and I almost never get a nice, accurate exposure reading from my 20D or nor now my 5D unless I use something like center weighted, aim for the most average brightness of the scene, and have a gradual light to dark transition in the scene--something like taking a picture of a boat and it's mast about 10 minutes after sunset. But then if I expose to the right, I lose color saturation, although I may save detail in the shadows.
This is utter balderdash. If you're "losing color saturation" you are either overexposing and clipping at least one color channel, or adjusting image brightness in Photoshop instead of using the exposure control in the RAW converter, or doing something else wrong. I've shot over 120,000 frames with digital cameras, and I have yet to find a situation where a frame with less exposure was superior to a frame with more exposure, unless the frame with more exposure had clipping.
-
If you are seriously proposing that the appearance of the image on the little non-color-managed LCD on the back of the camera is a more reliable indicator of proper exposure than the histogram, you are sadly mistaken.
This is utter balderdash. If you're "losing color saturation" you are either overexposing and clipping at least one color channel, or adjusting image brightness in Photoshop instead of using the exposure control in the RAW converter, or doing something else wrong. I've shot over 120,000 frames with digital cameras, and I have yet to find a situation where a frame with less exposure was superior to a frame with more exposure, unless the frame with more exposure had clipping.
[a href=\"index.php?act=findpost&pid=80974\"][{POST_SNAPBACK}][/a]
If you had read the previous replies, you'd understand that I meant yes, if you expose too much to the right, you can lose information from over exposing. And this can pose a problem is you rely on your histogram in high contrast settings.
It is only my experience that my histogram is unaccurate in many high contrast instances, either under or over exposing as shown comparatively in the LCD. Is the LCD more accurate than the histogram--I'm not interested in that argument because there are too many variables to account for and definitions to go voer before we can even start. Also, I can fix the problem using exposure comp and bracketing. But when I see a nearly black LCD image--except for the sunlight clouds--and the histogram shows a "correct" exposure, then I know it's lying--period.
I don't know what else to say on that subject except that my eyes may be very bad, or my camera is broken and will not expose corectly in high contrast situations.
-
More likely, your camera is set in such a way that the histogram isn't as useful as it might be. Read this article (http://www.visual-vacations.com/Photography/exposure_metering_strategies.htm) and tweak your camera settings and do the test under "Using The Histogram To Properly Judge Exposure". It may help your camera histogram be more useful to you.
-
More likely, your camera is set in such a way that the histogram isn't as useful as it might be. Read this article (http://www.visual-vacations.com/Photography/exposure_metering_strategies.htm) and tweak your camera settings and do the test under "Using The Histogram To Properly Judge Exposure". It may help your camera histogram be more useful to you.
[a href=\"index.php?act=findpost&pid=86146\"][{POST_SNAPBACK}][/a]
Going there now. Thanks for the link.
OK, I have some questions for you. The article says, "I recommend setting contrast to its minimum value. . . ." Does this mean set it to negative numbers, or just 0?
I have all my jpg settings at faithful, which is 0 all the way across.
-
Going there now. Thanks for the link.
OK, I have some questions for you. The article says, "I recommend setting contrast to its minimum value. . . ." Does this mean set it to negative numbers, or just 0?
I have all my jpg settings at faithful, which is 0 all the way across.
[a href=\"index.php?act=findpost&pid=86319\"][{POST_SNAPBACK}][/a]
I think it is minimum possible value, it depends of your camera firmware.
Some have negative number, other scale from 0.
Thierry
-
That should have been on the very first digital to offer RAW output. I'm still waiting. These manufacturers play us for idiots.
[a href=\"index.php?act=findpost&pid=79308\"][{POST_SNAPBACK}][/a]
The problem is complicated by the fact that WB will change the blown status of the channels, won't it?
To be able to use a RAW histogram in the field fully would implicely require us to think about WB at that time... if we don't, then it won't be much more accurate than a jpg based histogram... but we like RAW because we think that we can forget about WB in the field... argh... :-)
OK, AWB used as a base for RAW histogram would probably be a good approximation...
Regards,
Bernard
-
The problem is complicated by the fact that WB will change the blown status of the channels, won't it?
To be able to use a RAW histogram in the field fully would implicely require us to think about WB at that time... if we don't, then it won't be much more accurate than a jpg based histogram... but we like RAW because we think that we can forget about WB in the field... argh... :-)
OK, AWB used as a base for RAW histogram would probably be a good approximation...
Regards,
Bernard
[a href=\"index.php?act=findpost&pid=86361\"][{POST_SNAPBACK}][/a]
Bernard, I like to think - based on what I do when I remember - that WB when shooting RAW is essentially a non-issue. I carry both an ExpoDisc and a credit-card size Gretag COlor Checker. Snapping a frame with either one of them every couple of hours during a shoot, or whenever the lighting conditions change appreciably provides the data need to adjust all the photos taken around it. There doesn't need to be an issue about getting the "right" colour with this approach. The only remaining issue is whether that is the DESIRED colour, and at this point judgment intervenes over science. You can neutralize the warm glow of a snowy mountain at sunrise, but who would want to do that? At least RAW capture gives us the choice to be as mechanical or artistic as we wish.
-
To be able to use a RAW histogram in the field fully would implicely require us to think about WB at that time...[a href=\"index.php?act=findpost&pid=86361\"][{POST_SNAPBACK}][/a]
Not at all. Camera WB settings have no effect on RAW captures in most cameras. A RAW RGB histogram would only tell you how you're exposing each channel.
For cameras that alter amplification per channel based on the WB setting, the data would still be useful, and can only help.
-
The problem is complicated by the fact that WB will change the blown status of the channels, won't it?
To be able to use a RAW histogram in the field fully would implicely require us to think about WB at that time... if we don't, then it won't be much more accurate than a jpg based histogram... but we like RAW because we think that we can forget about WB in the field... argh... :-)
Which is why I recommend using a fixed white balance that matches the JPEG-based histogram to the RAW data as closely as possible. A RAW histogram won't require you to worry about WB while shooting, it will simply accurately inform you which channel(s) are about to blow out.
-
Which is why I recommend using a fixed white balance that matches the JPEG-based histogram to the RAW data as closely as possible. A RAW histogram won't require you to worry about WB while shooting, it will simply accurately inform you which channel(s) are about to blow out.
[a href=\"index.php?act=findpost&pid=86380\"][{POST_SNAPBACK}][/a]
Yep, you are correct, WB isn't an issue. My bad.
Regards,
Bernard
-
Which is why I recommend using a fixed white balance that matches the JPEG-based histogram to the RAW data as closely as possible. A RAW histogram won't require you to worry about WB while shooting, it will simply accurately inform you which channel(s) are about to blow out.
[a href=\"index.php?act=findpost&pid=86380\"][{POST_SNAPBACK}][/a]
Upon furter thinking about this, I think you are completely correct in this regard, with one caveat. The histogram must be able to accurately tell you when you are about to blow out highlights. If so, then you would want to expose to the right as much as possible, which would render your highlights as good as you can get, and your shadows as good as you can get. Then you can always under expose, if you need to--as when shooting high contrast scenese, such as a sunset--to bring out more color in the sky and clouds, and clip the shadows to black if necesary. Put another way, if you can get an accurate reading using your camera and histogram, expose to the right to retain as much dynamic information as you can.
-
Upon furter thinking about this, I think you are completely correct in this regard, with one caveat. The histogram must be able to accurately tell you when you are about to blow out highlights. If so, then you would want to expose to the right as much as possible, which would render your highlights as good as you can get, and your shadows as good as you can get. Then you can always under expose, if you need to--as when shooting high contrast scenese, such as a sunset--to bring out more color in the sky and clouds, and clip the shadows to black if necesary. Put another way, if you can get an accurate reading using your camera and histogram, expose to the right to retain as much dynamic information as you can.
That's the purpose of the test I described in my article; figuring out the exact exposure interval between the histogram indicating blown highlights and RAW clipping. As long as RAW isn't clipped, there is zero benefit to reducing exposure any further; you do not lose color saturation if you expose just below RAW clipping and then use a negative exposure setting in your RAW converter.
-
Yep, you are correct, WB isn't an issue. My bad.
Pobody's nerfect...
-
That's the purpose of the test I described in my article; figuring out the exact exposure interval between the histogram indicating blown highlights and RAW clipping. As long as RAW isn't clipped, there is zero benefit to reducing exposure any further; you do not lose color saturation if you expose just below RAW clipping and then use a negative exposure setting in your RAW converter.
[a href=\"index.php?act=findpost&pid=86543\"][{POST_SNAPBACK}][/a]
This is generally true of high-key and normal-to-high-contrast subjects. Converters don't always deal gracefully with exposure adjustments below -1 or so, though. They don't seem to understand the concept of exposing to the right, at least for low-contrast subjects where you can go way to the right. -4 exposure in ACR should theoretically render clipped RAW data at mid-grey or a little darker, but will render it at 255, anyway, stretching the extreme highlights like bubble-gum stuck to the ceiling. An "Exposure" control, IMO, should just be a scaling of the RAW data, not a combination of that and a Curves tool, which is what ACR seems to do.
-
Something I think you all will find very usefull, expecially for those who shoot action and therefor cannot blend exposures,
Back to the topic of White Balance (WB) and improving the Expose to the Right (ETTR) method.
The point of ETTR is to maximize the amount of the exposure which is in the most sensitive part of the camera's sensor without clipping the highlights to the point where the image is not salvageable.
There is a way to improve upon this --- apply the ETTR method to each color channel seperatly using a colored filter on the camera.
Ever notice that the noise levels in the shadows seem to be different for each channel?
We know that the RAW data is captured the same regardless of the WB setting in the camera. However we also know that the true WB of the scene does effect the ratio of light hitting the Red, Green, and Blue pixel elements in the camera.
Also, I suspect that there is another larger factor at play, the camera's Red, Green, and Blue pixel elements might have a different base sensitivity to light.
So I did a test. I took some RAW files (from the Canon 5D), one captured before dawn (blue white point) and one captured with indoor lighting at night (yellow/orange white point), and converted them using dcraw (http://cybercom.net/~dcoffin/dcraw/), which can be used to simply dump the raw linear data from the capture with no white balance adjustments (into a 16bit tif). Basically so I could see exactly what the camera was capturing.
What I found was that the output tifs have a very green tint to them regardless of the scene's true WB. Also I have noticed that with the Canon 5D most of the noise seems to be in the Red and Blue channels (try shooting with the 5D's long exposure noise reduction turned off). The data supports the theory that the camera is much more sensitive in the Greens.
When you use ETTR, at least with the 5D, it is simply the Greens that limit how far you can push your exposure to the right. The Reds and Blues will still be exposed to the left and hence have much more noise than the Greens. The RAW converter when adjusting the WB is simply scaling the Reds and the Blues to increase the intensity to match the Green channel to the proper WB.
Now if I had used a Magenta filter on the camera to drop the exposure level of the Greens, it would push the exposure of the Reds and Blues to the right as well, providing a much better capture in terms of noise (at the expense of a slightly longer exposure time or larger apature, and having to hand correct the WB later in the RAW conversion).
Each type of camera, not sharing the same type of CCD or CMOS sensor array, probably has a different base sensitivity to the RGB channels. So you could probably run through the same method I did, and figure out the perfect type of colored filter for a given range of scene WB, to maximize the ETTR method for all color channels and get a much lower noise image.
-
What I found was that the output tifs have a very green tint to them regardless of the scene's true WB. Also I have noticed that with the Canon 5D most of the noise seems to be in the Red and Blue channels (try shooting with the 5D's long exposure noise reduction turned off). The data supports the theory that the camera is much more sensitive in the Greens.
[a href=\"index.php?act=findpost&pid=86580\"][{POST_SNAPBACK}][/a]
A Bayer array filter found in almost all digital consumer cameras results in 50% green, 25% red and 25% blue pixels. These are combined by the RAW-processing app. This might be the reason for the green tint in the minimally processed dcraw output, although it's impossible to say without knowing how dcraw does the processing. It also explains why digital cameras are more sensitive to green - it's not the sensor itself but the filter.
-
A Bayer array filter found in almost all digital consumer cameras results in 50% green, 25% red and 25% blue pixels. These are combined by the RAW-processing app. This might be the reason for the green tint in the minimally processed dcraw output, although it's impossible to say without knowing how dcraw does the processing. It also explains why digital cameras are more sensitive to green - it's not the sensor itself but the filter.
[a href=\"index.php?act=findpost&pid=86610\"][{POST_SNAPBACK}][/a]
The RAW data has a green or cyanish-green bias in most DSLRs, because the combination of the sensor and IR-cut and Bayer matrix filters causes a difference in sensitivity between the three color channels with full-spectrum white light. The green is usually about a stop more sensitive than the red, and 1/4 to 1/2 stop more sensitive than the blue. The fact that there are more green-filtered sensors has absolutely nothing to do with this. Green was chosen to be doubled because it is most sensitive (and most light sources have plenty of green, but may be deficient in red or blue), and therefore the most light will be collected. If there were 98% red pixels, 1% blue, and 1% green, the green channel would still be the most sensitive, and the RAW data would still have a cyan-ish green cast. There would just be extremely poor resolution in the green and blue channels.
-
Green was chosen to be doubled because it is most sensitive (and most light sources have plenty of green, but may be deficient in red or blue), and therefore the most light will be collected. If there were 98% red pixels, 1% blue, and 1% green, the green channel would still be the most sensitive, and the RAW data would still have a cyan-ish green cast. There would just be extremely poor resolution in the green and blue channels.
[a href=\"index.php?act=findpost&pid=86630\"][{POST_SNAPBACK}][/a]
Another reason for more green pixels is that the eye is most sensitive to green.
-
Something I think you all will find very usefull, expecially for those who shoot action and therefor cannot blend exposures,
Action is the hardest place to use color filters, unfortunately, since you are often running on a tight photon budget, needing a fast shutter speed, and possibly also some DOF for sudden changes in subject distance. If, however, you were already operating successfully at a lower ISO, you could go up an ISO and still get better results, I think, as the image is only as strong as the noisiest color channel.
Each type of camera, not sharing the same type of CCD or CMOS sensor array, probably has a different base sensitivity to the RGB channels. So you could probably run through the same method I did, and figure out the perfect type of colored filter for a given range of scene WB, to maximize the ETTR method for all color channels and get a much lower noise image.
[a href=\"index.php?act=findpost&pid=86580\"][{POST_SNAPBACK}][/a]
I've been aware of the magenta native WB for a few years now, and I've stopped holding my breath, waiting for filter companies to come out with digital versions of daylight and tungsten filters. Falsehood propagates faster than truth, and one of the fastest propagating falsehoods is that "digital eliminates the need for color filters". Most DSLRs have very similar native white balances, even Canon CMOS vs Nikon CCD (multiplying the red channel by 1.9 and the blue by 1.4 in the RAW data of almost any DSLR should get you close enough for exposure purposes; small tweaks in the converter can make up for any differences). A single series of filters for most DSLRs should work well for many of them.
Again, filters don't help unless you can get a good exposure with them. Better to have the red channel one stop from "the right" than to have all three channels one and a half stops from "the right" with a filter.