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RAW vs. JPG: Correcting under/over-exposure

I was reading a discussion over at Flickr the other day about how shooting in RAW mode saved some under-exposed shots. Accepted wisdom seems to be that correcting under and over exposure is much easier/better with RAW than JPG. Without making any judgments, I decided to try it out and see if it was true.

I shot the same scene from a tripod 19 times. The first shot was with the correct exposure as a baseline. From there I shot 6 frames, each under-exposed by one full stop from the previous shot (i.e. the last shot was 6 stops under-exposed). I did that in JPG Fine and then in RAW. I also shot 3 over exposed in both JPG and RAW (last shot was 3 stops over-exposed). Then I attempted to correct each of the under/over-exposed images using Adobe Lightroom. For the under-exposed shots, I just let Lightroom figure out the exposure by clicking the Auto Exposure button. For each of the over-exposed shots, I manually adjusted the exposure and highlight recovery sliders until I got the best result. No other adjustments were made (e.g. color or white balance). JPG optimization settings in camera were set to Normal, white balance was Sunlight. The camera is a Nikon D70.

Here are the results. Each of the images below is the JPG version. Roll your mouse over the images to see the RAW version. One thing you’ll notice aside from the exposure differences, is that the color of the JPG versions is more vibrant. It’s a visible example of the kind of processing your camera does to an image during the JPG conversion process. Pay more attention to the exposure, detail, and noise levels in the comparison images.

Exposure test target
Correctly exposed baseline 1/30 @ f/2.8

Under-exposed

Roll over image for RAW version.

Exposure test
1-stop under
Exposure test
2-stops under
Exposure test
3-stops under
Exposure test
4-stops under
Exposure test
5-stops under
Exposure test
6-stops under

Over-exposed

Roll over image for RAW version.

Exposure test
1-stop over
Exposure test
2-stops over
Exposure test
3-stops over

Conclusions

It should be immediately apparent that the ability of the D70 to capture low-light detail is much better than its ability to capture highlight detail. Even at six full stops under-exposed, we’re still able to make out the subject. The 3-under photo looks much better than the 3-over photo. This makes sense since digital sensors are typically much better at recording detail in dark areas than in highlights.

Overall, I give a slight edge to RAW for recovering detail in under-exposed photographs. I say “slight” because you have to under-expose by four stops or more before it becomes an important factor. At 3-stops under, the corrected JPG still looks okay.

However, RAW is apparently much better than JPG at recording highlight detail, even at just one stop over. The over-exposed RAW images revealed much more detail in post-processing than the JPG versions. Even in the highlights of the under-exposed photos, the RAW version reveals more detail.

So, which is better? Well, if you routinely under-expose by four or more stops or over-expose by one or more, then shooting in RAW could help you correct those photos. Also, if you’re not sure how you should expose, then you should err on the side of under-exposure since under-exposed shots are easier to correct. But, if you expose correctly in the first place (or even within one stop either direction), you should be able to get great shots out of the camera no matter what file format you use.

John Watson

John is the original founder of Photodoto, but after running it for 4 years he had to focus on different things. If you're interested in what John has been up to recently, you can check is personal blog or browse his photo blog.
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