Raw files – what affects them

There is a myriad of camera settings that affect a photograph. How many of these changes actually affect the raw files is a matter of debate for some and confusion for most. The common word is that none of the camera settings actually affect the raw files and these are only important if saving photographs as jpg. Is this true? Let’s explore in some more detail.

Raw files

Often called digital negatives, raw files are without any doubt, the best format to save photos in the camera while clicking. It does give a lot of control over photographs and post-processing is the way to ensure the best possible results (Post Processing RAW). Post-processing and photo-editing is the equivalent of darkrooms nowadays. So shift to raw if you are still clicking jpg (Image File Formats – Basics).


Factors which affect raw files

In this article, I am discussing the settings from the camera menu but for clarity’s sake, let me further emphasize what factors invariably affect your raw files. Anything and everything that affects the light reaching your sensor affects the raw files. The focus, depth of field, angle of view, movement of the subject during the time of exposure, lens distortions… everything affects the raw files. Raw processors and photo-editors have various controls to correct many of these but the fact remains that these affect the raw files.

An interesting aspect is the color temperature of the scene. Though the color temperature of any scene can be corrected by either placing the correct filter in front of the lens or by correcting the color temperature in the post-processing (Balancing Act (in Color)). This has been the convention since the film days but there is a small catch. Imagine a yellow circle on a white sheet, lit up in yellow light. The circle will fade into the background because of the incident light’s color and no amount of color temperature correction will show the circle again. The correct way is to use proper color balanced lights where possible. Changing the color of incident light (light falling on the subject) is always better than correcting the color of reflected light (light from the subject reaching the camera). Anyway, this was just a parallel thought that crossed my mind.

Coming back to the factors affecting the raw files, ISO is also a matter of confusion. There is a new generation of cameras where the noise performance within a range of ISOs is the same. In such cameras, ISO setting within this range has almost no effect on the increase in noise levels. This ISO invariance can be helpful especially while trying to recover shadow details or trying to change the exposure while processing the raw file. Though ISO invariance is present in many new cameras, I still find an increase in noise even when I increase the ISO within this range of ISO invariance. Unfortunately, camera manufacturers do not provide this range in their specifications. Do experiment and find out the effective range for your own camera. As an afterthought, when you are at it, try to find the best ISO for your camera. Quite frequently it is not the lowest even if the sensor does not show ISO invariance.

Another aspect of the way ISO works on digital cameras is the widespread wisdom of ETTR (expose to the right of histogram). Clicking raw with ETTR and then correcting the exposure back during post-processing seems to help by reducing noise (though sometimes at the expense of EV range / dynamic range).

Another variable that is sometimes overlooked is the ambient temperature and sensor heat. One of the factors that cause noise is sensor-heat. Yes, cameras are more prone to noise in summers than in winters. Try to keep your camera cool and the sensor will reciprocate by delivering better quality images.


Camera settings that affect the raw files

ISO setting may affects the raw files as I have discussed above.

Over-Exposure (by varying ISO) If the image is overexposed by varying ISO, in most new cameras, this will help in reducing noise when the overexposure is corrected back to normal while post-processing. Photographers obsessed with night photography and star trails frequently use this method. There is a small catch though. By doing so, the dynamic range suffers.

Over-Exposure (when the ISO is kept minimum) There is no effect on noise (as happens in the above method) but the loss in saturation and dynamic range will occur.

Under-Exposure – Correcting extreme under-exposure will introduce a lot of noise and colorshifts in almost all cases.

Cropping that happens while trying to use DX lenses on an FX body. The Nikon cameras shift to DX mode and the images captured are therefore smaller in size. The information from outside of this is discarded.

Long exposures lead to noise. For calculating the long exposure noise, the camera immediately after completing a long exposure captures another shot with the shutter closed. This second exposure captures only the noise since the shutter is anyway not open.  The camera’s software then uses the information from this second exposure to remove the noise from the first exposure. This second exposure and long exposure noise reduction happens on the fly and modifies the raw files.

Exposure compensation and Active D-lighting. These settings also affect raw files. Exposure compensation is self-explanatory (see the explanations above) but why Active D-lighting affects the raw files is beyond my understanding. All that I know is that using Active D-lighting mode even while clicking raw, tends to darken the overall images. Once I understand the reason behind this, I’ll update this article.


Autumn - Clicked using a compact camera and saved as jpg

(Maple trees in Autumn – Clicked using a compact camera and saved as jpg. Though the article is about raw files, inserted this photograph here to break the monotony of text)


What does not affect the raw files

Everything that I have not included above, does not affect the raw files. Color balance, saturation, sharpening, color space used, picture control settings, high ISO noise reduction, lens distortion correction, vignette correction, etc are all included as extra information with the raw file. These recommended settings do not actually alter the raw file.

These values do work as a start-up point in many compatible raw converting programs. Nikon’s nef files when opened with their own Nikon Capture NX-D software, have all these controls set. If the image is directly converted to jpg, all these settings which have been copied from the camera settings, that existed at the time of clicking the photograph, get applied. The resulting jpg, therefore, looks very similar to the raw on the camera preview screen.

And yes, the camera preview screen! This shows the raw files with all the above settings applied even though none of them actually affect the raw file. The histogram and all the relevant data shown on the preview screen are also as per the settings on the camera even though the raw file remains untouched.

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