Exposure - Am I exposing correctly.

[jwbryson1]

I've been shooting my DSLR regularly for about 3 years so I'm not really a "noob" per se, but I do have a question on proper exposure. In short, when I use photo editing software and hit "autocorrect" on an image for example, the photo is sometimes brightened a lot by the software. Sometimes it looks better, other times it does not. The histogram shows proper exposure, the photo looks good and so it appears that the photo is exposed properly. Nevertheless, sometimes I get these changes that may or may not look better.

Am I to assume that the photo is **not** properly exposed because some software editing tool lightened it when I hit autocorrect? That does not make sense to me.

For the record, I generally shoot direct to JPEG because I don't have the time or the inclination to shoot and revise in RAW. I'm not interested in a JPEG vs. RAW discussion either.

Thoughts?

 

[Overread36]

Auto correct is not perfect - its only applying a statistical model of changes to your photo to try and present something which is technically "better". However it ignores any artistic control or influence and often can make a photo look worse rather than better because its not able to see beyond its technical viewpoint. It's far better to take control yourself and learn to make basic changes to your photos according to what you want not what the software wants.

In addition you need to lean what a proper exposure really is;
1) First up you've got a proper technical exposure according to the histogram - this is where you've the most light data on the right side of the graph, without overexposing (ie hitting the furthest right hand side). This isn't trying to make a nice bell shaped curve like in statistics, but one shaped with the most light data weighted on the right hand side.

2) Artistic/real world - this is where you come in as the photographer - the above model for a technical exposure works, but it ignores many factors which will cause you have limits. You might need a certain shutter speed or aperture to create an artistic effect/control over your photo - you might have a complex scene with large areas of shaded components - you might want to over/under expose from the model. etc.... This is where experience, control and a bit of experimental shooting comes into its own.

 

[EmbassyProBooks]

Like Overread said, auto correct is not perfect. It is just what the computer has decided is right. You may have purposefully under or overexposed an image. It has no way of knowing that. If you hit auto exposure and you think it makes the picture "better," you might want to mess around with exposure when you are shooting. Take one photo at what you think is the correct exposure, then one a step underexposed and one a step overexposed. It woll help you see the differences side by side.

 

[photocist]

My guess is that the program is correcting contrast and saturation rather than exposure.

 

[vtf]

I stopped early on using it. I now just compare what I did manually with the auto for kicks once in awhile.

 

[jwbryson1]

Auto correct is not perfect - its only applying a statistical model of changes to your photo to try and present something which is technically "better". However it ignores any artistic control or influence and often can make a photo look worse rather than better because its not able to see beyond its technical viewpoint. It's far better to take control yourself and learn to make basic changes to your photos according to what you want not what the software wants.

In addition you need to lean what a proper exposure really is;
1) First up you've got a proper technical exposure according to the histogram - this is where you've the most light data on the right side of the graph, without overexposing (ie hitting the furthest right hand side). This isn't trying to make a nice bell shaped curve like in statistics, but one shaped with the most light data weighted on the right hand side.

2) Artistic/real world - this is where you come in as the photographer - the above model for a technical exposure works, but it ignores many factors which will cause you have limits. You might need a certain shutter speed or aperture to create an artistic effect/control over your photo - you might have a complex scene with large areas of shaded components - you might want to over/under expose from the model. etc.... This is where experience, control and a bit of experimental shooting comes into its own.

Point 1 above is VERY interesting to me. I've read in detail about using histograms and what they represent, how to read them, etc., but I've never seen this comment before or considered this to be the "correct" approach. But in light of my issue (pun intended), what you say makes some sense to me. It's not the statistical bell curve that is "correct" necessarily because there could be areas of the photo that are still too dark and perhaps that what the "autocorrect" feature is doing. I never thought about it that way. I've always thought that I had "correct" exposure when I did not hit the far left or the far right side of the histogram but only came close.

This entire discussion assumes that I'm not doing anything "artsy" and trying to get some strange effect. Let's just assume that I'm shooting a no frills landscape at 6pm and want something simple.

So assuming you are correct, how do you adjust your camera to get light skewed to the right side?:hail:

 

[KmH]

I recommend you read: http://www.adobe.com/digitalimag/pdfs/linear_gamma.pdf.

Bruce somewhat expands on that article in the introductory chapters of his book; Real World Camera Raw with Adobe Photoshop CS5.

To get into the real nitty-gritty, read: http://wwwimages.adobe.com/www.adob...ly/prophotographer/pdfs/pscs3_renderprint.pdf

 

[Overread36]

So assuming you are correct, how do you adjust your camera to get light skewed to the right side?:hail:

Well if the histogram represents exposure over the whole scene, if you want more on the right you've got to expose more of your shot. That can mean one of several possible approaches:

1) Wider aperture - lets in more light - at a cost of less depth of field
2) Higher ISO - more sensitive to light - at a cost of more noise
3) Slower shutter speed - again letting in more light - at a cost of less freezing of motion

so if you've got your camera stable (eg on tripod) and you're shooting a typical landscape scene the easiest is to let the shutter speed slip slower (either using exposure compensation or in manual mode). This brings you to the point about the camera meter itself not being perfect; understanding how its reading the light is important, but its also important to understand that is can be tricked and also has no artistic concerns - thus sometimes you do have to go against the meters reading to get the exact exposure you want - this is part about learning how your camera reads light and in what situations you have to adjust that reading.


Also remember the idea of exposing to the right is about light gathering - you gather as much of the light as you can an then - in editing - you can always tone back the brighter areas (not overexposed areas of course as these only have white data and no details to restore - note RAW mode will give you a bit more of a window on this than JPEGs will). The concept here is that you can darken areas without cost in your photo - but adding light (ie making areas brighter) in editing reveals more noise in your photo.
Also remember that getting the whole photo to hit the right hand side of the histogram is not always possible - shaded and bright areas in a photo will nearly always be present - this is where (if one desires) one can use methods such as HDR to get a full even exposure over all areas from combined shots - it is also a good method to use when the scene itself cannot easily fit into the cameras dynamic range (the range from the brightest to the darkest spots).

 

[subscuck]

You also have to be aware that sometimes what you're shooting may be mostly shadow and mid tones with very little high light. In this case your histogram will be towards the left for correct exposure. In a case like that, if you try to force it to the right, you'd be massively overexposing.

 

[clanthar]

So assuming you are correct, how do you adjust your camera to get light skewed to the right side?:hail:

He's correct -- you can stop assuming.

To get max benefit from a digital camera exposure you want to expose as much as possible while retaining detail and color in your diffuse highlights. This get's tricky because the worst exposure error you can make is to blow those highlights. The word then is precision.

Terms like expose to the right concern me as they seem to suggest that there's another way to go. The original question here is: am I getting correct exposure? You are if you're exposing as much as possible without blowing the highlights. Don't call it exposing to the right call it correct exposure.

You can trust that the engineers who built your camera know the above and have done their best to get you there within what they consider reasonable limits. In other words the meter in your camera has been designed to get you a correct exposure. Use the camera's histogram display and consider activating the clipping warning for additional support.

All this still leaves you hanging however for three reasons:

1. Your camera meter is reading the light reflecting back from your subject and as such works on the assumption that your subject meets the criterion of "average reflectance" that the meter is programmed for. When your subject deviates from the assumed average you get a degree of error.

1. a) If your subject includes a backlight does your camera know that? A light source is not the same as a reflective subject -- your meter will err.

2. You're shooting in camera JPEGs. The data captured by the sensor is being handed over to a collection of software algorithms in your camera known as the camera image processor. Camera image processors -- bottom line: they don't work very well. You can expect this to happen regularly: You'll get a good exposure, the RAW data will contain the necessary detail and color in your diffuse highlights and the camera image processor will trash the exposure and blow the highlights for you.

3. You can't capture everything you see. Dynamic range (lighting contrast) is variable. Think about the light on an overcast day. The contrast is low and the scene is easy to capture -- no problem getting correct exposure. The dynamic range in a scene can easily expand beyond our hardware's ability to deal with it. Dappled sunlight breaking through to the dark forest floor -- there is no correct exposure for that, and your poor camera won't know what to do with it. Then the image processor will trash it twice just out of spite.

Joe

 

[jwbryson1]

KmH, I printed this yesterday and read it and found it very interesting. Thanks for the post. "Expose to the right." I like that.

 

[jwbryson1]

So assuming you are correct, how do you adjust your camera to get light skewed to the right side?:hail:

He's correct -- you can stop assuming.

To get max benefit from a digital camera exposure you want to expose as much as possible while retaining detail and color in your diffuse highlights. This get's tricky because the worst exposure error you can make is to blow those highlights. The word then is precision.

Terms like expose to the right concern me as they seem to suggest that there's another way to go. The original question here is: am I getting correct exposure? You are if you're exposing as much as possible without blowing the highlights. Don't call it exposing to the right call it correct exposure.

You can trust that the engineers who built your camera know the above and have done their best to get you there within what they consider reasonable limits. In other words the meter in your camera has been designed to get you a correct exposure. Use the camera's histogram display and consider activating the clipping warning for additional support.

All this still leaves you hanging however for three reasons:

1. Your camera meter is reading the light reflecting back from your subject and as such works on the assumption that your subject meets the criterion of "average reflectance" that the meter is programmed for. When your subject deviates from the assumed average you get a degree of error.

1. a) If your subject includes a backlight does your camera know that? A light source is not the same as a reflective subject -- your meter will err.

2. You're shooting in camera JPEGs. The data captured by the sensor is being handed over to a collection of software algorithms in your camera known as the camera image processor. Camera image processors -- bottom line: they don't work very well. You can expect this to happen regularly: You'll get a good exposure, the RAW data will contain the necessary detail and color in your diffuse highlights and the camera image processor will trash the exposure and blow the highlights for you.

3. You can't capture everything you see. Dynamic range (lighting contrast) is variable. Think about the light on an overcast day. The contrast is low and the scene is easy to capture -- no problem getting correct exposure. The dynamic range in a scene can easily expand beyond our hardware's ability to deal with it. Dappled sunlight breaking through to the dark forest floor -- there is no correct exposure for that, and your poor camera won't know what to do with it. Then the image processor will trash it twice just out of spite.

Joe

Joe, understood completely. Good point with the forest/light scenario in which there is no "correct exposure" for this--you either expose for the forest and blow out the light or expose for the light and the forest is left in the dark. In that case, it appears that taking a photo is nearly pointless.

 

[Dao]

I know it has been discuss. But the following links show why sometimes Auto is not a good idea since the computer do not know what the photographer want to show on the photos.

Juza Nature Photography