DSLR Photography Forum

I'm reviewing a new camera, and seem to be having some troubles with blown out whites in some of the images. One example is this one - it wasn't an overly bright or sunny day, and the sun was behind the clouds.

The trees on the right look correctly exposed, but yet the sky and path on the left are blown out, and loses a lot of detail.



Closer view:


What do you think? Is it a camera problem or a user error (scene not metered correctly)?

Actually come to think of it, I think it's just me (or the metering...)

Or is it?

This is how the Canon Pro1 handled the same scene on a different day:



Yet you can see that the shot with the Pro1 was on a much sunnier day (look at the shadows on the ground)...

Well the first does appear to be a little overexposed. I think much depends on where you meter (and what metering mode you use.) If this was an "evaluative" or "matrix" type meter, then it doesn't appear to be doing its job very well. But if you were spot metering the darker parts of the tree, then overexposure is what you might expect.

Would have been evaluative then lol....

*type type type - review*

I have a low end digital Canon A70. I always use a manual mode and try for a one stop underexposure. I get good saturation of color but I get noise when I compensate for the lack of beta using software.

Wow Don - underexposing by one stop seems pretty aggressive. You'll really increase noise by doing that, and it's not a software problem but just the way digital sensors work. If you haven't seen this article, it's worth a look:
http://www.luminous-landscape.com/tutori...ight.shtml

Hm... instead of using manual and underexposing, how about using exposure compensation? Would that achieve the same effect? That way you could leave it on all the time and not have to meter manually...

I agree - 1 stop is a bit drastic... but if it adds to your style, then go for it

i think he may mean he uses Tv or S mode with -1 exposure compensation.

The A70 does tend to overexpose a little. I usually set it at -1/3.

as for the pictures, it's rather hard to compare the two since they were taken at different times. the shadows do look stronger on the ground in the second, but the first looks like there may have been more clouds, which reflect/diffuse the sunlight, giving the whole scene its rather flat look.

That pic does look overexposed somewhat, and the previous suggestions of underexposing slightly are useful ones IMHO.

Interestingly I was reading an article (can't remember where) recently about some of the more subtle differences between digital and film photography. One of the differences they discussed was that digital cameras really do have a tendency to wash out highlights and lose a lot of detail there (compared to film, which can maintain subtle detail in highlights better), but digital can better store detail in dark areas than film it seems. The conclusion was that to "be on the safe side" and maintain the maximum amount of detail in an image, you are better off slightly underexposing when taking a digital image (to prevent the wash-out of highlights) than over-exposing it. In contrast, you were better off doing the opposite for film (to prevent loss of detail in the shadows).
But the article did not discuss the issue of noise, which as slejhammer points out, usually becomes more of an issue with digital the darker you go.
But I'm not convinced there is a correlation between increased noise and decreased exposure. The existing noise might become slightly more visible in the dark areas of a photo, but I can't see that underexposing a photo by using a faster shutter speed or closing the aperture will actually *increase* the noise, unless the signal has to then be amplified in post-processing.
Certainly when you are taking photos where there is less light and you need to switch to higher ISO's you will get more noise, as the noise is being amplified along with the signal, and is most visible in the dark areas of the photo. Similarly when you need to lighten parts of an image in photoshop or whatever, it will enhance the noise along with the actual detail you want.
But in a well-lit scene where you can use the lowest ISO setting then noise shouldn't really be a problem in most cases, and the benefit of increased highlight detail could be well worth it.
There will always be dark areas in photos (with or without any noise problem), and underexposing a bit will just mean there is slightly more of them
You can always use Noise Ninja to remove noise, but there is no easy way to put detail back into a big washed out section of a photo where every pixel is 255,255,255 (or 65535,65535,65535 if you are working in 16-bit).

To get an idea of the amount of over-exposure your pic has, take that pic and put it into your favorite image editing suite and run whatever "auto-equalize" or "auto-level" function it has, and you'll see it dramatically darkens the shadows and gives heaps more contrast (but still leaves the sky washed out). Run that other image taken on the Canon through the same process and you'll find it won't change it as much because it was better exposed to start with.

Although the sun might have been behind clouds, common sense tells us that an overcast day can still have a lot of glare, and the clouds act like light diffusers. When you look at the sky on a sunny day with just a few clouds present... which is lighter, the sky or the clouds? The clouds obviously are, so when the sky is full of clouds, although the total amount of light falling through the clouds onto the trees might be less, the sky itself could be a lot lighter because it is full of clouds.

Other things that may be affecting the photo are possibly infra-red and/or UV light. sensors are often by nature quite sensitive to light outside the visible spectrum. This is used as a feature with "0-lux" or "night vision" functions on video cameras and so on, but is usually seen as a problem for digital still cameras as it can interfere with the image produced. Most cameras these days have built-in filters to block out this light (particularly infra-red), but perhaps the one you were testing did not?
I actually enjoy taking infra-red landscape photos, and ironically this filtering "feature" that is included in most digicams these days is a hindrance for such photos. In fact I think Canon has released a special version of their 20D in Japan which *doesn't* have a filter that blocks out Infra-red light, specifically for this niche market.

Anyway, just my 2c. I am still learning this stuff myself, so feel free to shoot me down if I'm just regurgitating rubbish But please be gentle, this is my first post here.

Cheers
Adrian

Hiya Adrian,

Welcome aboard! (I feel like Captain Stubing)

There are a couple of techniques for repairing blown out images, the best method I find is shooting raw and then combining the under and overexposed images. The biggest problem with lightening an image too dark is the amount of noise you can get.

Thanks for the welcome StudioJ

Unfortunately I haven't yet been able to work with "raw" images (I have been using mainly an Olympus C-750UZ which doesn't support them), so although I can't wait to play with the added flexibility they allow (I've been waiting for the EOS350D to be released, which was supposed to be today!), I can't comment on them with any experience except to say "I'm sure you can do lots more stuff with them, and I can't wait to have a fiddle".
But having said that, I can see your point about combining an under and over-exposed image of the same scene to put detail into the blown-out areas. I have manually used a similar technique to add colour to some of my infra-red photos (ie using a tripod, take an infra-red photo of a scene, then carefully remove the filter without disturbing the camera and take a normal photo of the same scene, then combine the two images in various ways on the PC). It can give interesting results in certain situations.

I absolutely agree that lightening an existing image will increase noise propotionally to the lightening (as it simply amplifies everything), but perhaps I wasn't clear... as I meant that if you can avoid lighting the image afterwards then you should get no increase in noise simply by under-exposing it. The image of the trees given as an example at the start of this thread was over-exposed to start with, so reducing the exposure it would not necessitate lightening later.

I guess my point should have been that it is important to get the exposure as close to what you want as possible when taking the photo... if you need to lighten it later then it will increase noise (as stated by you and others), but the other side of the coin is that if you need to darken it later then you might have lost detail in the highlights - and digital could be more prone to this than film.
Would that be a fairer and clearer statement? Perhaps a little obvious stating that "correct exposure is important"
I guess that's why bracketing was invented. I'll just crawl back in my hole now. hehe

Cheers
Adrian

ps: I noticed you are in Perth also. I am hoping to buy a Canon 350D this week, and if you can suggest anywhere local I should try then I'd be most grateful. So far, Camera-Land Camera House (In Leederville) seem to be my best bet. They have given me a "rough" price around $1699 but can't confirm it until they have stock. I bought my Olympus C750 and an EOS 300 film camera from them previously, and they were the cheapest I could find in both cases (and I could get the olympus at wholesale prices from DMA, but these guys were still cheaper at the time). I've also noticed however that some of their other cameras are NOT so cheap as they used to be, so I'll wait and see.

Hey there Kombisaurus! Welcome to Shuttertalk!

Thanks for all the info... lots of considerations there. I used to shoot film too, and I always had the impression too that digital tended to overexpose a bit. Good to see it's not just me...

Regarding shops in perth - I'm from Melbourne myself, but we've got a few members from perth. There's a thread here talking about some shops:
http://www.shuttertalk.com/forums/viewtopic.php?id=1580


Once again welcome to the forums - hope you enjoy yourself here. If you need anything, just PM me.

Camerahouse in Leederville should give a good price for it, they have a pretty high turnover of stock. You could try Camera Electronic Sales as they seem to be cheap for quite a bit of gear lately too.

Love that Kombi! I wanted one for a surfy girl shoot a few months ago and couldn't find anyone with one where the heck were you!

Hi Julian,

Thanks for the welcome.
I'll try to dig up where I read that article, it was quite interesting reading.

I am fairly new to photography, but have been playing around with computer imaging and graphics for quite some time as a hobby going back to the mid-80's (using Deluxe Paint on an Amiga 500!) hahaha.. those were the days... I remember causing a bit of a stir with the external examiners who discovered my entire year 11 art portfolio comprised of digital images. People wouldn't bat an eyelid about that today, but back in 1987 when I was in year 11, quite a few people didn't know what to make of it.

I still can't quite work out why it took me so long to get into photography, but I guess it had a lot to do with the fact that decent affordable digital cameras are still a fairly recent phenomenon, and before digital cameras, the line between computer imaging and photography was a lot more distinct than it is today.
Anyway, the end result is that I feel quite comfortable working with digital media, but am still coming to terms with many of the issues specific to photography.

I hope I can contribute something to this forum, but I also hope I can learn a lot from other people's experiences and the advice they give.
Thanks for having me.

Cheers
Adrian

ps: Thanks also for the link to that thread.

Hey StudioJ,

Thanks for that info about Camera Electronic Sales - I'll check them out.

It's so frustrating... the official release date for the 350D was today, but I expect most places won't have them in stock until the end of the week or longer.

I was all set to buy a Nikon D70, then just stumbled across a rumour that Canon would be superceding the 300D, and the more I dug around the more it seemed I should wait for the 350D.
I guess even if the 350D isn't as good as everyone seems to expect it to be, it should at least mean the 300D and likely D70 will drop in price more.

StudioJ Wrote:Love that Kombi! I wanted one for a surfy girl shoot a few months ago and couldn't find anyone with one where the heck were you!

haha.. Thanks. My poor old kombi is a bit rough around the edges these days, but the thought of a bunch of skimpy surfy girls draped all over it would certainly cheer it up a bit
I have been meaning to repaint it again soon, and am planning a camoflage theme this time (ie it would have camo colours where it is currently blue, but I'd keep the cream colour above the window line).
Next time you need one, let me know

I can also help hook you up with some faster cars if you need them for shoots and have trouble finding them - particularly jap imports (Supras, 180SX's, GT-Four Celicas, etc). As well as my kombi, I've also got a Supra and am active on a few forums with other people in perth who drive similar cars.
In fact, the supra guys had a meet last weekend (I wasn't in Perth so couldn't attend), but they posted pics of the cars that were there:

http://www.waix.net/~mofo/main/pictures/...%20Cruise/

Cheers
Adrian

Kombisaurus Wrote:But I'm not convinced there is a correlation between increased noise and decreased exposure
... unless the signal has to then be amplified in post-processing.

Whether you amplify the signal in post-processing (adjusting the image tone curve or levels) or in-camera (increasing ISO), the result is the same. Actually, it can be worse if you underexpose and then bring up exposure in post-processing, because there is simply less "signal" or information in the shadow areas. GIGO.

P.S. Welcome!

Hi slejhamer,

Thanks also for the welcome. You're a very welcoming lot here.

I think perhaps I wasn't too clear in my original post.
I happily accept what you say, that switching to a higher ISO will simply amplify the signal (and noise) in-camera and so effectively give the same result (and noise levels) as brightening the image in photoshop afterwards. In fact, in my mind I would tentatively include almost all processing the camera does to the image between leaving the sensor and being written to the memory card as being a form of post-processing, which I guess is why DSLR's almost all have the ability to write unprocessed raw image files. Of course when discussing it with other people, it is less confusing to seperate "in-camera processing" from "post-processing", where the latter is what happens on a PC after taking the images off the camera.

I guess when I wrote that original post I was thinking in relation to the original image used as an example - that of the over-exposed trees with the washed-out sky (sorry, I know Julian thought the trees were correctly exposed, but I think they are over-exposed).
That image could probably benefit from having less overall exposure, and would not need any signal amplification as it would not need to be lightened either by increasing ISO in-camera or on the PC afterwards (ie: it was too bright to begin with). In the case of that example photo, giving it less exposure by closing up the aperture or going for a faster shutter, or ideally by decreasing the ISO, should address the problem of the sky without introducing more noise (in fact there would be less noise if the ISO was decreased), but only as long as the image did not then need to be lightened to make it acceptable.

Or alternatively the photo might have simply been taken on a rubbish camera! hehe.. if in doubt, blame the gear!

Cheers
Adrian

Kombisaurus Wrote:blame the gear!

When my wife cooks something that doesn't taste right, she blames the pans!

Apologies to slej, I didn't click on his link (http://www.luminous-landscape.com/tutori...ight.shtml) and read that article.

Of course I forgot that digital sensors are linear, yet the way the human eye perceives light is exponential (each stop is double/half the light of the previous/next one) - so of course digital cameras *do* capture more detail in the lighter areas than in the darker areas, as the highest stop represents 1/2 the entire sensor's dynamic range, the 2nd highest stop represents 1/4, and so on - the low stops are much more susceptible to posterisation and noise.
So in this sense, Slej is absolutely correct in suggesting that the signal-to-noise ratio tends to be much lower in the darker areas (simply because of the way the signal gets converted from a 12-bit linear representation into an 8-bit exponential representation) - so as far as reducing noise goes, you are better off to over-expose and then tone it down in post-processing - and this result can even produce less noise than a "properly" exposed image with no post-processing.

But the original problem at the start of this thread was with the highlights.
With film, as the light reaches the extreme highlights, the film gradually becomes less sensitive to this change in brightness. The result is that detail remains in the highlights, just with a reduction in contrast.
Digital sensors however have no such "shoulder", and simply represent all levels linearly up to their maximum, at which point they clip the signal abruptly.
the result is increased contrast in the highlights right up to the limit of the sensor, and then they are clipped and suddenly become totally blown out and lose *all* detail.

So blowing out highlights is a big no-no for digital, as once a signal is clipped at the sensor, the details cannot be salvaged.
But there is some help at hand, as it appears that most RAW images actually contain more dynamic range than is represented in the JPG output, so often you can extract up to 1/2 stop more detail out of the highlights if you work with the RAW image instead of the JPG. Half a stop is better than nothing, but certainly not enough to make you throw caution to the wind.

So the "Epose to the Right" lesson in that luminous landscape tutorial that Slej pointed to really would give you better results - in theory anyway.

But... is it worth all that effort for each photo to save a bit of noise? If you could automate the workflow - perhaps re-flash the camera with a reprogrammed exposure algorhythym and script something on the PC to expose the pics properly later - then maybe it is? Sounds like a lot of hard work though...
I love working in Photoshop and can see the benefit in working with good RAW software, but I also love it when good photos come out of the camera without needing anything done to them.
My Olympus C750UZ is pretty ordinary when it comes to noisey low-light and high-ISO photos... I keep it stuck on 50 ISO and switch to 100 when I need to. 200 is for emergencies only and if I need 400 then I'll just walk away shaking my head. My tripod and remote are my best friends in low-light. Even if it had a RAW mode, it would still only improve things slightly.
There is another much simpler approach to solving this problem if you, like me are suffering from noisy pics - buy a better camera!

hahaha.. see, it really does come back to "blame the gear"!

Well, actually it comes down to "take advantage of the technology". Something like a 350D can take photos at 1600 ISO with less noise than my C750 does at 50 ISO in low light...
Things have come a loooong way in the last couple of years, and while you might think its unfair to compare a 350D to an Olympus P&S, the fact is that my C750 retailed at AU$1200 when I bought it, and I just ordered a 350D for AU$1470. Both cameras fill a similar price-bracket, yet they are worlds apart in most other aspects.

...if only I could buy new skills as easily (and cheaply) I think I need to stop talking and go out and actually take some photos now.

Cheers
Adrian