Canon EOS20D: Under expose to prevent highlight blowout?

[mendel_leisk]

Having done about 400 exposures with my new 20D, almost all in "P"

mode, letting the camera decide exposure, I see a dismayingly high

percentage of shots have some degree of highlight blowout. Also, when

reviewing a lot of my pictures, I often find the scene as captured by

the camera seems "brighter" than my recollection.

 

I appreciate careful metering of the highlights, perhaps coupled with

bracketted exposure, could prevent blowout. Also, review of shots on

the lcd, to look for blowout and inspect the histogram, would help.

But, I think this would be awkward and cause me to miss shots.

 

Is anyone resorting to exposure override: slightly underexposing to

avoid highlight blowout, and if so:

 

1. Do you do so constantly, or just for contrasty situations?

 

2. By how much do you underexpose?

 

3. How does your shadow detail react?

[beauh44]

Hi Mendel, Here's my .02 cent's worth:

 

1) I check my histogram and never shoot in P mode. 99 percent of the time I'm in Av mode and frequently dial in plus or minus exposure compensation.

 

2) It depends on the subject, the histogram and the effect I want to achieve.

 

3) Very well when shooting in RAW mode. You'd be surprised at the shadow detail you can retrieve when shooting RAW.

 

In short I think the best advice I could give would be to abandon shooting in P mode and learn to use the histogram to your advantage. Good luck!

[bens]

shoot with a 10d. they say digital imagery is like slides, you always have to protect against blown highlights. like it or not, checking the histogram while shooting is critical to avoid too much information on eithr end of the spectrum. i almost always shoot in manual and underexpose often, such as when the histogram indicates i have a problem, or in situations where i know harsh light will be problematic. i pull out details in the shadows in photoshop. there's a fair amount of detail retained there if you are careful.

[bens]

. . . meant I shoot with a 10d.

[KenPapai]

Ditto on what Beau wrote: get OFF the P mode and shoot RAW and use software to help recover some shadow detail. You can always set up a tripod (if you're shooting outdoor scenics) and use layers by shooting three separately exposed images and then layer them over each other for an extremely high dynhamic range final image. Can you say 32-bit? ;-)

[mike_hodson]

Read up on "Expose to the right"...it basically says that the best way is to get as much exposure as you can...before you blow the highlights. Then, as said, it's fairly easy to bring up the shadow detail.

[picturesque]

I do exactly that when wanting to shoot fast. I use AV, ambient underexposure compensation coupled with the 580EX set as normal (which for me is +2/3 flash compensation when using flash evaluative mode). Typically I use between 1-2 stops of minus compensation, depending upon how contrasty the scene. Play with it and you'll soon get a feel for how much. Sometimes I compensate the flash too, knowing that above 10EV, the camera will use auto fill flash reduction. Of course, I still check my histograms and use manual mode and a hand meter if I have the time. Also, in even shade, I do not use ambient EC but pull back a lot on the flash. Shadow detail is fine--don't know what you mean exactly.

[PuppyDigs]

Beisdes using RAW and taking control of metering there is one more thing: how you judge

your images. Be sure you use a calibrated graphics quality monitor. Many monitors fall

short in this area and thus shadows appear blocked up and highlights blown, when in fact

they are fine.

 

Finally, prints can't render the full dynamic range either, so you may have to "compress"

the dynamic range to fit the display medium.

[ajweiss]

I just shoot RAW and forget about it. 99.9% of the time, the dynamic range is enough to

cover what I need. A little work in the RAW converter saves a lot of worry in the field. If I'm

really worried about the shot, I might shoot another one underexposed a half or a whole

stop. Most of the time I don't.<div></div>

[ajweiss]

100% crop, levels boosted.<div></div>

[awindsor]

Notice the histogram and blinking highlight warning depend on the converted RAW file for the preview. That is to say that the in camera parameters matter. For that reason I have my parameters set to contrast -2. This means that you don't get a warning until the highlight is pretty blown. You might be able to extract some detail with negative exposure on your RAW converter but it is not guaranteed. On the standard parameter setting blinking warnings occur in areas where it is easy to extract details using less agressive conversion parameters.

 

I have to say that except in very high contrast I find that the 20D underexposes or rather that it doesn't expose to the right. To increase the shadow detail I dial in positive exposure compensation. I almost never get blinking warnings except when in a high contrast situation (particularly shots at night) or shots into shadow during the day. In these cases there is no good solution and if possible I will blend two shots.

 

Though Puppy Face has achieved zen oneness with his camera I still chimp the histogram in tough situations.

[michael_w.]

Mendel,

 

For as long as I've been shooting with digital (whether P&S or SLR)--and as others have mentioned--I've always found it necessary to underexpose subjects lit by direct sun by up to a full stop (usually 1/3-2/3). For strongly backlit scenes you'll need to add EC if you're not using a flash, depending on what you want to expose properly.

 

It's much easier to use Photoshop to add in digital fill-flash or open up shadows than it is to bring back blown highlights, even if you're not shooting in RAW (a separate shadow/highlight function has been added in CS). How much exactly is always going to be subjective, but over a time you'll get a feel for how much EC was necessary when you look back at your exposures if you take note of what the lighting conditions were at the time. Cheers!

[mark_chappell]

I have a 10D and a 1D II. For both, I normally rely on Tv mode and usually have a 1/3

(1D) or 1/2 (10D) underexposure dialed in for routine subjects. This gives good shadow

detail and avoids highlight blowout most of the time. If there is high contrast, and I want to

presever highlight detail, I increase the underexposure.

 

I almost never use the histograms (probably a mistake, even though it is time-consuming

and distracting), but those simple rules work in the vast majority of circumstances. In

extreme conditions (high contrast, strong backlight, etc.), I bracket exposures a lot.

[thomas_sullivan]

I would agree with the "shoot in RAW, get out of that P mode and into Av mode or Tv or even Manual, and expose to the right just below the highlite blow out" scenario.

 

Now, owning the 20D, and having used a few other digital cams of friends, I too notice what Alistair notices about the 20D. Canon must of precompensated for blow out control (maybe a bit too much), because I too, on the 20D in Av mode have my exposure compensation usually set to +1/3, and this takes care of maybe 95% of my pics. I double checked the accuracy of this by shooting a white wall and it indeed did come out exactly in the middle of my 20D histogram (as it should, as meters are designed to expose everything to an average of middle gray)

[robin_sibson1]

It's not too hard to recognise when you are going to have a problem handling a near-white highlight, like sun reflections off water, and sometimes it doesn't matter much if they do blowout a bit, since you can't really expect to capture the full dynamic range of scenes like that. In my experience there is a more subtle effect to watch for, which is single-channel blowout, most commonly in the red channel. This happens with bright orange-red colours, as found in sports clothing and flowers, and it happens surprisingly easily in scenes that look quite innocuous. The effect is to render orange-red and scarlet as bluish-red, presumably because the blue channel is still coping at the point where red has hit the stops.

[mark u]

Many people are deriding P mode as if it had something to do with metered exposure - this is only true for ambient exposure for flash - otherwise metered exposure is identical to that which you would get in any other mode. P mode simply selects an aperture and shutter speed consistent with the metered exposure according to the program line for the ISO in use. You can change the combination, and you can use exposure compensation, and you can use any metering mode. Av and Tv are about taking control of different aspects of the image such as depth of field and motion blur.

[antony_bichon]

I am back from a 2 day 18 mile hike/camping with the 20D. I shot 99% of the time using the evaluative metering system and I have to admit that this metering system tends to overexpose and blow out the highlights in full day conditions.

I was mostly in green forest, blue sky, clear ground/trail condition. I was constantly between -2/3 to -1 stop. What puzzled me and pushes me to comment here is that the histogram had room on the left hand side (luminance histogram) and clearly showed compressed highlights...

I bought the 20D new a couple of weeks ago... I am going to try it more and see if this is a thing to keep in mind.

Any comments?

[bellavance]

If you shoot in P Mode, and blow the highlights, you will blow the exact same highlights if you shoot in Av or Tv or even Manual modes.

 

I almost always shoot in P Mode, except when I want to control depth of field or use a tripod (Av) or want to control speed blur (Tv), but I also almost always use Raw Mode (to get a little more exposure leeway) and I bracket and/or check my histogram.

 

Pierre

[steve_unsworth1]

Buy an incident meter and shoot in manual mode?

[jim_larson1]

Yes, nothing wrong with "P" mode.

 

You do need to learn to check histogram after shots: It will quickly improve ALL your photos.

 

When in doubt, I just set the camera to -1 Exposure compensation. I rarely go wrong when I do that.

[mendel_leisk]

On the face of it, I too think there's nothing to be gained (regarding highlight blow-out) by using either TV or Av exposure mode instead of P. Unless you do want a particular shutter speed or aperture. Inderectly, I do think there is some benefit, in that you tend to be more aware of the exposure settings. Particularly if you've chosen a smallish aperture, and want ensure you haven't set yourself up for a time exposure :)

 

FWIW, I am shooting raw.

 

As I said at the outset, if you have the time, and the subject is static, careful manual metering, paying attention to the highlights, test and bracketed exposures, is surely the way to go.

 

Too bad the camera doesn't have a "blow-out mode":

 

*Uhoh, significant 255/255/255 area, stopping-down 1/3 stop. Still there, stopping down to 2/3 stop. Blow-out gone, take picture*

 

I think Les Sarille's comment about dslr's being similar to slr's with slide film is spot on, that's what I keep thinking when I review my shots.

 

Last week's picture of the week, the jackel with prey, was taken with a 20D, if memory serves. The photographer noted that he used 2/3 stop underexposure compensation.

 

I'm going to try stopping down, per some responder's suggestions, mabe coupled with bracketing, fill a card and see how they look. Look for shots with that little troublesome splash of sunlight, that sort of thing.

 

Thanks all!

[mendel_leisk]

Shooting an 8"X10" Kodak grey card, evenly lit by fluorescent, then displaying the the (uncached) histograms in PS CS I get the following values, with AWB:

 

Exposure adjustment Median Value

 

-1___________________89

 

-2/3_________________105

 

-1/3_________________124

 

0____________________138

 

+1/3_________________149

 

+2/3_________________157

 

+1___________________189

 

If a grey card should be 128, it looks like -1/3 exposure compensation would be closest to that value, and would slightly reduce the chance of blowout, also.

 

Perhaps someone else could try this and post their results. Maybe, for example, a different light source would change things.

[mendel_leisk]

Alistair, do you think setting processing parameter does anything to the potential information in the raw file, or is it just affecting the lcd display, how much blow-out warning, and how soon? I think you're saying the latter, am I reading it right?

 

In other words, if you have set proc. parem. 1 (more contrasty jpeg production), the display will warn of blow-out sooner than with p.p. 2 (lower contrast, more natural jpeg production), but the content of the raw is actually the same. Am I right there?

[robin_sibson1]

If you are shooting RAW, the only parameters you need to worry about are the ISO setting and the exposure. Everything else is recorded but serves at most as a default setting during post-processing. That's just one of the many attractions of RAW - you don't need to worry about making good choices of a hatful of parameters when you are actually trying to take pictures.

[mendel_leisk]

Thanks, Robin. That's what I thought, but wasn't sure.