panorama software,virtual tour software
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2006-06-18
#1

nikon 8400 - consistent exposure

Once in a while, when I do a 3 picture pan (Nikon 8400, FC-E9, MrotatorB), I get different image color tones.  One the images comes out darker or lighter and that shows when I stitch.

My settings are:

Lens:Fisheye, ISO 50, AE-Lock, Noise Reduction ON, image ajustment Auto,

White balance meter - centered -

White balance would be Sunny in the demo picture:

www.invideo.ca/demo.jpg    -  see band each side of the sun

I included a interior picture to show you picture quality with same settings (but incandescent WB)

www.invideo.ca/demo2.jpg  

Take note that both picture have already be size optimized (200-300Kb)

Questions:

-Should I use Auto Whitebalance

-Should I use 100 ISO or more when outside ? - (100 iso gives me NOISE when low light inside)

- My camera allows to take 8mb picts -  I currently set it to do 5MB.  Would it we advisable to take 8mb anyways ?

Any recommendation would be appreciated as I'm doing 250 panoramas of a Resort and I'd like to offer the best results possible.

Thank You.

 

 

 

 


I see Fragged people
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2006-06-27
#2

Well, I knew that Smooth would fall asleep again......LOL......mabey one day I will get a "brownie point" from Smooth....LOLOLOL

As far as the specific problem pointed out above with an exterior scene taken with direct sun (sun iris) in the image I disagree that the over exposure of the sun frame is caused by white balance.

It is the light that makes the exposure not the CCD or "sensor". True, white balance refers to the "temperture" of light but the reason this problem occures in direct sun is not because you are using a standard white balance setting such as "direct sun" or "incandescent". This setting will only effect the "color cast" of the image not the exposure.

This problem is about differences in exposure between frames not the color temperture. It doesn't matter what white balance you use as long as it is set the same for each frame. It could be flourescent for that matter and the frames would still be different in exposure.

The issue is how much light is collected through the lens at each frame asuming a constant shutter/aperture. When the Iris of the sun is beamed through the lens the sensor is simply getting overloaded. The diods get very excited and move tremendously fast. There movement is translated into "frequency's" that are then translated into color. White light is made of all the color spectrum and each color has a specific freaquency. When the sensor records the data anything outside of the dynamic range of the sensor or more acuratly the "frequency response" of the sensor you get no data which equals the color white. Black would be the other end where no frequency response is recorded and again there is no data.

This problem is increased with cameras that have small sensors. These cameras are just awsome at captureing color data "within their dynamic range" but that range is directly related to the size of the sensor. Bigger sensor equals more dynamic range because there are more sensors per milimeter. There are other more technical aspects that effect dynamic range but as far as "point and shoot" cameras with small sensors are concerned it is the size that matters.

Now put on a FC-E8 or E9 lens and we now are attempting to record ALL the light from a 180x180 FOV. This works great when the suns iris is not in the image. But when it is the whole situation changes.

Refration does matter. It happens to all lenses. And very wide angle lenses are especially effected by this. Refraction does effect exposure in wide angle lenses because of the amount of light that is being resolved ( the ability of a lens to squeeze or compress light waves closer together without loosing wave lengths in the process).

When refraction occurs it not only effects sharpenss as related to aperture size but also effects the exposure due to light bouncing around in the lens and then being sent back to the sensor. However this effect is more of suttle problem and not necssarily the main reason but combined with an overloaded sensor it all adds up.

I am curious to know if the kind of exposure problem occurs when shooting RAW where white balance is not an issue? I bet that it does happen. It has to according to the way the sensor records data. But I could be wrong....lol

Regarding AE-Lock - I think all other setting besides shutter and aperture should be set to something constant that you change when needed. That is why I always say to use full manual. For me AE-lock is a pain in the butt. I really is much easier to set up a "custom shooting menu" and then use manual to expose your shot.

Metering with the camera-----if you have to...The camera aint that smart most of the time. You will get much more accurate expusures if you do two things. #1 learn how to read a histogram and #2 pay attention to the lighting and remember what kinds of scenes need what exposre settings. If you take


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2006-06-27
#3

Gen. Lee,

You may have a brownie point. This is not to encourage you into longer novels though! But to teach you that you can be rewarded for getting to the point. (LOL)

You yanks must get paid by the word or something? I bet this comes from your education system where teachers tell you no less than "X" about of words for this essay.......

All you say is correct and articulate. Congratulations you get a

Doing, is the best learning - get on with it.

Regards, Smooth


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2006-06-27
#4

Well put General.  Light intensity and Histograms.. yes

OH  and Smooth IS a wake and reading the forum.. good on ya !

Ah now lets see.. quietly counting the words !

Dave


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2006-06-27
#5

Yeah and it's now 4.55 am in Australia!

fifty five, fifty six, fifty seven, fifty yawn.... (LOL)

Regards, Smooth


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2006-06-27
#6
  SUN RISE  in Land of the Oz
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2006-06-18
#7

Good morning Digital,

Hmm the indoor and outdoor image you might try this approach.  The Sun or bright wall lights are called Primary Light.  Bright windows fall in this catagory too.

Setup your tripod and put your back to the prime light  Turn the camera 90 degrees left or right for image #1.  Turn on or reset the AE Lock.  This 90 degree position will be your first image.  Automatic Exposure Lock then will light meter 50% of the  of bright and dark scene area.  The average light meter (bright and dark) and shutter speed settings will then be reused in image #2 and 3.  Be sure to RESET the AE Lock for the next panorama location.  An indoor setting will not be good for an outdoor scene.  Usually I RESET the AE lock after taking the 3rd image.. then the camera will be ready for the next scene.

In Panoweaver click on the TOOLS menu item.. and tell it to blend the widest overlap area.  I think the widest setting is 15 pixel seam area for a 3 shot.

If you are doing commercial - then BIGGER images are ALWAYS better. 

RAW images are called a digital negative image.  What the sensor saw is what you will get.

In Adobe PSCS2 and Adobe Camera RAW converter, load ALL 3 .NEF  images at one time.  Then you can WHITE BALANCE adjust ALL images to be the same value.  For example, click through all 3 images to see their values.  #1 4800  #2 5200  #3 5000.  Then add them together and divide by 3 or an average white balance of 5000.  Then manually make all 3 images 5000.

You can also adjust the EXPOSURE  balance to help provide even blending.

Hope that helps.


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2006-06-18
#8

WARNING - This is a long post. Don't read it if you rnot interested in the finer points of this problem. The solutions are at the end if you are in a hurry.

Never use Auto white balance. This can change between frames and cause exposure problems.

With non DSLR cameras avoid upping the ISO at all costs. This will introduce noticeable noise. ISO is a setting to make the CCD more sensitve to light. It is used only in low light or very fast shutter speeds in combonation with small apertures to capture stop motion in bright light or manage depth of field in motion shots. In low light Use 50 ISO and choose a larger aperture and slower shutter speed.

Always take the largest megapixel image you can.The more data the better your final image will be. If you want clear, crisp images you need to start with the most amount of data possible. When sizing down or resampling you will be loosing data so starting with more data in the beggining means more data at the end. Actually it means more "quality" data not necessarily raw megapixels.

AE-lock will work as many use this feature, however you really should learn how to use the camera in full manual mode and choose your aperture and shutter speed according to the situation. Meter if you like first to see what the camera "thinks" is the proper exposure and then go to manual and set the aperture and shutter to that reading. Then start shooting. This will cause the camera to use the setting you picked on every shot until you change them. AE-lock simply locks the aperture and shutter speed to what the camera picked on the first shot so that the other shots are taken with the same settings.

Do not use auto focus. Set focus to infinity. If you use auto focus and you get closer than say 2 or 3 feet to an object like the corner of a wall that shot will be out of focus at distance. This refers to the "hyperfocal distance" of the lens. Look that term up for a better explanation.

Note: Sun iris focusing onto the CCD is really a problem for NON slr cameras because they do not have a shutter mirror but this can still occur in DSLR cameras if shooting repeatedly in direct sun.

This is a classic example of "light refraction" within the lens and an overworked ccd sensor.

Wide angle lenses especially one at 8mm gather the light from a 180 circle. Next comes the "resolving" power of the lens. This takes the light and compresses it into an area that is rendered onto the CCD. The more resolving power the crisper the image will be. All of this light is being compressed and when it is invariably refraction occures. Most of the time we hear of refraction as related to aperture performance. For example small apertures (large f numbers) on wide angel lenses generate refraction at the sharp edges of the aperture blades. This is due to the oblique angle at which light is bent through the lens. Some of it cant quite make it through the aperture hole and strikes the edges instead of passing directly through the aperture hole. The light is striking these edges and bouncing around in the lens. This can cause a "soft image" in ALL situations but it is the direct sun at issue here because of the AMOUNT of light not necessarily the aperture size.

In this case the light or rather the brightness and more importantly "amount" of light is the one of the culpits. The sheer volume of light is huge. Think of it like playing with a magnifying glass. On a bright sunny day you can focus the light through the glass to the point at which it will burn a hole in a leaf or fry an ant (for you "Sid's out there- lol). On a cloudy day there is not enough light to generate enough heat to burn. The dot is the same size but there simply is not "enough" of it.

When you push this much light through a lens invariably this brings out the inherint faults of the lens itself. The other end of the scale is low light and again faults in the lens will rear their ugly head.

Lens makers attempt to coat the elements within the lens with non reflective materials in an attempt to allow as much light as possible to pass through the elements without actually reflecting off the elements. Their is a point at which some light will still be reflected and this is related to the amount and brightness of the light. When this reflection occurs you get "refraction" within the lens. The refracted light is bounced around in the lens at can again be sent back through the lens. If this happens you will sort of over expose the image somewhat. With non wide angle lenses something say around 35mm or higher this is not usually a problem because you would rarely if ever point the lens directly at the sun. And if you did you would use some kind of light restricting filter anyway.

But on a wide angle lens this is not something you can control because the lens is "wide angle" and will therefor most likly get the sun in the image. At least as far as panoramic images are concerned.

Note for Sigma users: The sigma 8mm actually generates a full circular image but on 1.5x sensors this circle is cropped creating what we call a "drum image". When the lens is pointed or alighned vertically with the sun this cropping also contributes to the exposure problem. If you looked at two circular images from this lens one being taken directly at the sun and the other not at the sun both images would appear normal with normal exposure according to your choosen settings. Even if both images were taken with a corresponding aperture/shutter speed comb ( meaning an equal exposre for both) the sun image would still be over exposed compared to the second image.......culprit is again light refraction. When you crop a circular image you are taking out some of the light distrubution in the image circle. The image was meant to make a circular image not a drum image. This is a contributing factor but not the real reason for the problem.

The REAL culprit is the CCD in this case. The CCD heats up when it is working. Heat is the enemy of the CCD. The CCD begins to heat up as it is used and ambient heat from the camera body will further intensify this problem. You have about 5 minutes in direct sunlight before you camera will start to suffer from heat stress. It will even cause the camera to just suddenly shut off if you let it get too hot. Use a white towel to shield the camera until you are ready to shoot and when done immediatly cover it up or you are asking for trouble.

When the lens is aligned vertically with the sun and slightly off center as well the direct sun will be focused onto the ccd. The spot on the CCD will "immediatly" and I mean immedialty begin to heat up tremendously. The CCD becomes the ant and the lens becomes the magnifying glass. When this occures that spot transfers heat to the rest of the CCD. As the CCD gets hot it causes the electron collection diodes to basically stop working and when this happens they can not properly record color data. You loose data just like you do if you over expose an image. You can avoid this somehwhat by choosing a really fast shutter speed of  1/3000 or higher but not entirely because you still have to shoot 4 or more frames to complete the shot.  Another option is to use a gel filter (for sigma 8mm and nikon 10.5) on the back of the lens to control the amount of light in combonation with a fast shutter speed. It is worth noting that this prolem can occur in doors as well and does when using long shutter speeds in a dark room with poor lighting. The more you over expose the scene the worse this problem will be. It is best to go for a slightly under exposed image and color correct this later than to shoot what should be a"correct" exposure.

So my friends the problem stems from four things.

1. light refration

2. Amount of light being resolved

3. CCD temperture

and 4 (which I havent mentioned yet). - The angle or obliqueness at which the primary light source (ie sun) is being collected. When the sun is placed at the edge of the lens circle refration is increased. Light will bounce of the lens elements more easily at a sharper angle than strait on at the center of the lens.

Solutions:

1. As Dave states above set up the shot so that two of the images are evenly spaced as related to the sun. If this was a two shot situation you would "split" the sun by putting it directly at the edge of the frame so that the primary light source is evenly split between two frames. In three shot this is not possible. So you must split it between three frames. To achieve this one must make a judgemnt about how the light in the scene is being reflected from the environment. Examples are scenes with snow or white sand vs non reflective surfaces such as pavement and bricks or a white wall of a building that you happen to be next to. In four shot you have an easyier job because you have more overlap in frames and blending of the the images is easyier. In fact you are in luck if there is a bright reflective surface in the scene because this will help in reducing  differences in light refracton between frames. But solution 4 below is by far the best.

2. Use a gel filter in combonation with fast shutter speed.

3. Use only a fast shutter speed and be quick about shooting the scene. Cover the camera before shooting and immediatly after the scene is shot.

4. Find something to obsure the suns iris such as a tree trunk, light pole, tree limb, tree leaves, building overhang or some other natural obstruction.

By the way. Direct sun focused through your lens can in fact damage your CCD if allowed to be there to long. I never leave my lens uncapped outside while moving to different locations. You can get distracted by an inquisitve person or get caught up in composing you scene and all this time the sun is beaming onto your CCD.....bad...bad.

I hope you enjoyed this little short story. or Novel if smooth is reading this LOL

General Lee


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2006-06-19
#9

*Yawn*  lol

But what if you camera doesn't have a CCD?

No really, most of your issue comes from your white balance settings. Simply selecting "Sunny" or Incandescent" is not the answer and as was written in Gen. Lee's "novel" above you should never use "Auto White Balance".

You're best to set a "Custom" white balance for each panorama scene you wish to shoot. This can be done very easily with just a plan piece of white A4 copy paper. Take a shot of this white piece of paper in the most evenly lit area of your panorama scene whilst the camera is in "White Balance Learning Mode" (this set up procedure can vary from camera to camera) this educates the camera as to what is pure white under these shooting conditions. Once this is set. You can then following Dave's advise split the light over the lens when composing your shot for lighting conditions.

AE-L should be used as this not only locks aperture and shutter speed on the Nikon Coolpix cameras but also the ISO and colour temperature (Not so on DSLR's).

Be sure when setting your shutter speed to make sure you set it by your internal "Light Meter" on the shot that shows even light or split light as discussed above and then leave and lock (AE-L) for the consecutive panorama shots.

Shooting in manual focus or automatic focus will matter not unless you have objects closer to the lens from one shot to another. To play it safe set to manual "Infinity".

I will also stress that you will yield far superior results if you shoot RAW (.nef) and correct the images using Photoshop RAW converter. Doing this you can adjust the Exposure, White Balance, Vignetting, Chromatic Aberration across the series of shots. Yes it is more work but the results will always be far superior to those of .jpg's processed by your cameras inbuilt processor.

Good luck and we all hope to see your results soon.

Regards, Smooth


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2006-06-19
#10

WOW - You guys are awesome,  I'll try the proposed methods asap

Thank You.  


I see Fragged people
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2006-06-20
#11
Slightly hijacking the thread but I was wondering;

how do people cope with setting the white balance with a fisheye lens and a piece of white paper?

I always find a peice of a4 even held right up to it looks fairly small not covering/filling the frame and with 180 degrees your never going to fill the frame? Do you assume it only checks the balance on the center or set it with a different lens or something?