Metering

[paulph]

Hi folks,
I took two identical photos, in Live View and P, of bananas on the table. First photo spot-metered, second one centre-weighted. The spot-metered pic is lighter to look at - but the exposure details for the two photos are exactly the same, no difference at all! How can this be?

[paulph]

I'm using a D7000 by the way. Thanks for any insights!

[xpatUSA]

One of the odd things about mid grey is that sometimes 18% grey is mentioned.

John
-

Apparently 12.7% can get a mention, too. Something to do with headroom or summat.

Even odder when mid-gray in sRGB is 118/255 or 119/255 (I forget which, duh).

The well-respected Doug Kerr goes on about it quite a bit here:

http://dougkerr.net/Pumpkin/articles...eflectance.pdf
.

[dem]

Hi folks,
I took two identical photos, in Live View and P, of bananas on the table. First photo spot-metered, second one centre-weighted. The spot-metered pic is lighter to look at - but the exposure details for the two photos are exactly the same, no difference at all! How can this be?

Is it possible that the camera had changed the JPEG processing between the shots? This can happen in auto mode when the camera automatically picks up a "scene": one shot could have been treated as "indoors" and the other as "landscape", for example.

[Mike Buckley]

It would help if you would post both photos with EXIF information intact.

[Manfred M]

I've moved these posts from a two-year old thread and into a new one.

It would of course be helpful to see the images you are asking about, but I think I can make a fairly educated guess, based on how camera metering systems work. I'm going to oversimplify a bit.

Cameras use a reflected light metering system that requires a built-in assumption of what an average scene looks like, and if it were a monochrome meter, it would give you a "middle gray" as the "ideal exposure", regardless of what metering mode you are using. When metering a whole scene, this assumption is often fairly good, but if it is not, your shot will be either over exposed or under exposed. Trying shooting a scene that is predominantly blue sky, a white sand beach or a snowscape, and these will tend to be overexposed. Shoot a night scene and it will end up looking lighter than it really was. That is simply an issue with reflective metering and why your camera has exposure compensation capabilities.

So if your spot meter reading was on a point that was significantly darker or lighter than the the centre weighted metering area, the two exposures would be different. As the spot metered image was lighter than the centre weighted image, the spot you were metering would have been darker than the the centre weighted scene.

This is one reason that incident light meters are used for product and portrait photography. They measure the amount falling on a subject and are not "fooled" by the differences in reflected light.

[Dave Humphries]

Paul,

We need to see the photos and EXIF data so we can be certain of what you say.

What I think you're saying is that you have two photos, with same ISO, shutter speed and aperture, but one looks lighter than the other.

This is effectively renders the question of the metering mode used irrelevant.

Question is; was the framing (and hence image content) exactly identical? (e.g. was it shot from a tripod?)
Also that the light level didn't change momentarily; e.g. was that daylight, artificial or even flash?
Is it possible that this changed between/during exposures, unnoticed by you at the time?

Hence we need to see them both, with embedded EXIF data, so we can satisfy ourselves of some of these factors, at least.

Manfred is suggesting valid reasons why the two metering modes might give different answers, but I'm not sure that's what you're asking.

I have to say I believe I have also seen inexplicable differences in two exposures myself very occasionally.
What camera are you using?
Shooting RAW or jpg?
I could ask more, but the images with EXIF embedded would save a lot of time.

Thanks in advance, Dave

[paulph]

Paul,

We need to see the photos and EXIF data so we can be certain of what you say.

What I think you're saying is that you have two photos, with same ISO, shutter speed and aperture, but one looks lighter than the other.

This is effectively renders the question of the metering mode used irrelevant.

Question is; was the framing (and hence image content) exactly identical? (e.g. was it shot from a tripod?)
Also that the light level didn't change momentarily; e.g. was that daylight, artificial or even flash?
Is it possible that this changed between/during exposures, unnoticed by you at the time?

Hence we need to see them both, with embedded EXIF data, so we can satisfy ourselves of some of these factors, at least.

Manfred is suggesting valid reasons why the two metering modes might give different answers, but I'm not sure that's what you're asking.

I have to say I believe I have also seen inexplicable differences in two exposures myself very occasionally.
What camera are you using?
Shooting RAW or jpg?
I could ask more, but the images with EXIF embedded would save a lot of time.

Thanks in advance, Dave

Thanks everyone. I'll upload the pics - how do I embed the EXIF data? (first attempt) -Paul

[paulph]

Thanks everyone. I'll upload the pics - how do I embed the EXIF data? (first attempt) -Paul (apologies for double reply)

[Mike Buckley]

The EXIF info will already be embedded unless you or another site that you uploaded the images to stripped it from the files.

[Dave Humphries]

The method of producing a jpg for upload may also strip the EXIF data.

Just give it a go and we'll see what we can see

... but it would help if you tell us the software used; e.g. LR (LightRoom), PS (Photoshop) or something else.

[paulph]

Pic 1, spot meter.

[paulph]

Hi Dave,
I uploaded the two photos for comparison (I'm not sure where they ended up; I'm learning this site as I go along).
I'm using a D7000 and Photoshop. Even on the camera screen the pics look different from each other...my puzzlement is that the data are exactly the same!

[Mike Buckley]

Follow the upload information very carefully. If you used the TinyPic method, my guess is that you forgot the last step, which requires you to copy and paste the URL into the body of the post.

[paulph]

Actually Jpegs in iphoto.

[xpatUSA]

I'm using a D7000 and Photoshop. Even on the camera screen the pics look different from each other...my puzzlement is that the data are exactly the same!

Not possible unless the light changed between shots. Thing is, most cameras show only a tiny fraction of the "the data" that is in the file, so please don't be puzzled. When you upload the two images, I'll be glad to look at them with Phil Harvey's ExifTool which shows everything.

Actually Jpegs in iphoto.

What?

[Manfred M]

Not possible unless the light changed between shots

The light may not have changed between shots, but that doesn't mean that the different metering modes came up with the same exposure. This would account for the exposure differences.

Take a shot of a white card that completely fills the frame and then do the same with a black card that completely fills the frame. Chances are that both exposures will be just about identical (middle gray), rather than being what the subject looked like to you. This is of course the issue of using a reflective meter and why we have exposure compensation controls to over ride the meter reading. If the shot had been evaluated by an incident light meter, both would have come out looking right.

If the spot meter is pointed at a part of the image that is substantially darker or lighter than the whole scene, I would expect the two exposures to look quite different.

[Dave Humphries]

Actually Jpegs in iphoto.

There is no link to the photo in the post Paul.

The instructions you need are here, specifically; you have apparently not done steps 4 and 5.

Try again?