1

I'm a photography newbie, and would like to know what is the basic difference between exposure control and brightness (e.g. under Picture Control on a Nikon), but specifically when changing it in-camera, e.g. when shooting JPEGs. (I've seen this question discussed many times on various forums, but they all seem to focus more on post-processing in LR, Photoshop, etc.)

The way that I understand it, is that exposure control will control the brightness of an image before it is captured by the image sensor, by changing the amount of light falling onto the image sensor, by means of aperture or shutter-speed. Brightness (e.g. under Picture Control settings) on the other hand controls the brightness of the image after it is captured, by displaying / saving colours a shade lighter or darker.

For now, I don't need to go more technical than that - just wondering about the basic difference when working in-camera.

  • Some of the Answer you are looking for might be at - photo.stackexchange.com/questions/6598/… – thebtm Feb 28 '17 at 18:06
  • btm, unfortunately that post does not really answer my question. I have edited my question above to be a bit more specific. – JdR Feb 28 '17 at 18:44
  • 1
    What, exactly, is your question for us? – Michael C Feb 28 '17 at 18:51
  • What model camera? – Michael C Feb 28 '17 at 18:52
  • I just want to confirm that EC essentially affects brightness before the image is captured, whereas "Brightness" essentially affects the brightness after the image is captured. Camera is a Nikon D3100. – JdR Feb 28 '17 at 18:56
1

I just want to confirm that EC essentially affects brightness before the image is captured, whereas "Brightness" essentially affects the brightness after the image is captured.

Basically, yes. But it is not exactly that simple. It also depends on exactly what stage in the processing pipeline is "captured." Whether you mean "captured" raw data or a "captured" JPEG image produced using that raw data determines whether the more complete answer is "yes" or "no".

Short answer:

  • If you saved an NEF file containing the raw to your memory card the answer is Yes.
  • If you only saved a JPEG to your memory card the answer is No.

Aperture and shutter duration determine how many photons strike the imaging sensor. That is, they control how much light the camera collects. Of course, the brighter the light in the scene is, the more will be collected by the same Av and Tv. Well, unless you're considering a flash strobe that has a very short duration, in which case the Tv won't matter (unless it is shorter than the camera's sync speed in which case it will matter) and only the Av will determine how much of the light from the flash is allowed into the camera. See how quickly it ceases being so simple?

ISO and the camera's signal amplification determine how the electrical charge created by photons striking the sensor are translated to digital data in the form of what we call raw data. Everything else done downstream of the raw data is based on these digitized numbers. Changes made to the way these numbers are interpreted don't change the numbers themselves, they just change the way the numbers are processed to produce a viewable image.

The preview you see on the camera's LCD right after you take the picture is a jpeg preview generated by the camera based on the camera's firmware that includes algorithms used to convert the numbers in the raw data. Things such as black point, white point, color temperature and white balance, contrast, etc. are determined by the algorithms used to demosaic and convert the raw data. The jpeg preview, along with a list of the instructions used to produce it, is then attached to the raw image data in the NEF file.

What the various Picture Controls on your camera do is alter the set of instructions the camera uses to interpret the numbers in the raw data to create a preview image or a finished JPEG. Canon calls the same thing Picture Styles.

  • If you are only saving your images as JPEGs, the Picture Control settings used when you took the picture are "baked in" and can't be reversed later. So in a sense, these settings are "captured" in the JPEG image. Any changes you make when editing a jpeg image are based on the result of the Picture Control Settings used to create the original JPEG.
  • If you save the raw data, then the Picture Control settings affect the list of instructions saved alongside the data from the sensor. But they have no direct effect on the raw numbers themselves. The instructions can be altered later and a new interpretation of the same raw data can be used to produce a very different jpeg than the original interpretation produced in the preview image.

If we decide later to edit a raw file what we change are the instructions used to convert the numbers in the raw file. Even when we "save" these changes to the raw file we don't change the numbers in the original data obtained from the sensor. What we change is the set of instructions included with those numbers.

If, on the other hand, only the information in the jpeg is preserved then any further edits change the numbers contained in the jpeg file. But since the jpeg has a lot less information than the raw data did, our ability to change the image is more limited.

  • Thanks for the comprehensive answer, Mike - that's what I was looking for. For now I'm just saving the pictures as JPEGs, since I mainly want to play around with the camera and get more solid on the basics first. In that case - and just to recap - my EC (Av & Tv settings) control how much light falls on the sensor and how bright the image is in the raw data, while the "Brightness" setting changes the way the raw data is interpreted downstream and how brightly those colours are saved in the JPEG. – JdR Mar 1 '17 at 12:32
  • Also another question - how does this equate with the days of 35mm film? Aperture and shutter obviously are the same back then as now, in principle. But what about "Brightness", "Sharpness", "Contrast", etc. under Picture Control - I suppose that that was a combination of the type of exposure in the dark room, and also of the type of film that was used? (Plus if you could still confirm my "recap" in the previous comment please [even if it is very simplified].) – JdR Mar 1 '17 at 12:42
  • Av & Tv control how much light falls on the sensor. The ISO multiplier also affects how "bright" the numbers recorded in the raw data are. I used quotes because raw data is not really a viewable image at all. When you "view" a raw image on your camera what you are actually looking at is the jpeg preview produced by applying a specific interpretation to the raw numbers. When you open a raw image file with an editor you're looking at a very jpeg-like interpretation of the raw data based on the settings active at the time. Change the settings and you get a different interpretation. – Michael C Mar 1 '17 at 19:00
  • The film question should probably be asked as a separate question, rather than in the comment to an answer of this question. – Michael C Mar 1 '17 at 19:01

Your Answer

By clicking “Post Your Answer”, you agree to our terms of service, privacy policy and cookie policy

Not the answer you're looking for? Browse other questions tagged or ask your own question.