디지털 카메라로 사진을 찍을 때 가장 주의 해야할 문제 중 하나는 바로 highlight clipping이다. 필름에 비해 관용도가 좁은 디지털 이미지의 특성상 명부가 확 날아가 버리는 것이다. 필름의 경우 버닝 작업을 통해 어떻게든 표현할 수 있지만 애초부터 데이터가 0인 명부 사진을 보정하는 건 불가능하다. 우연히 즐겨 읽는 온라인 저널에서 다음과 같은 글을 발견할 수 있었다.
(빌 피어스는 최근 포토저널리스트들의 주요 관심사인 디지털 카메라의 문제점들을 다루고 있다. 지난 10월에 마침 M8의 이미지 프로세싱에 대한 내용을 게시하여 기억해 두었는데 정보를 공유하고자 한다. 나의 결론은 밑에서 확인 하시길.)
Nuts & Bolts
The Digital Journalist, October 2007
This goes against all we have been told about raw digital images containing the majority of their information in the brighter areas of the record and suffering in quality when dark images are brightened in image-processing programs. The common wisdom has always been to expose as much as you can without losing highlight detail and tame the brightness when you convert the raw file to a TIFF or JPG.
The problem for photojournalists has always been that it has taken careful metering and checking the histogram to make sure that you have that bright image that still maintains highlight detail. In covering breaking news, an experience often so hectic that your entire being is on autopilot, it is unlikely that you are going to use a handheld incident meter, check your histogram or bracket. And, just like you, the camera is going to be on autopilot – excuse me, program mode.
Underexposing the raw and correcting the JPG looked like it might be a good way to deal with digital photography's limited exposure latitude and informationless overexposed highlights. I ran some tests with an M8 and Capture One Pro and it worked.
The next question was, would it work with other cameras and other image-processing programs? The answer ... Well, sort of. OK, really, no. Photoshop offered the strongest corrections in the exposure and saturation categories, but you could see the image beginning to fall apart. Capture One didn't look as bad, but probably because you couldn't increase the exposure and saturation levels as much. Certainly you could salvage a shot in an emergency, but you wouldn't want to do it on a regular basis.
There has been a lot of speculation about the Leica M8 raw file. There is some reason to believe it is a 14-bit file converted to 8 bit, but with a difference.
An article about the M8 in KammaGamma states, "Obviously when converting 14 bits (or 16 bits) into 8 bits, data gets compressed all over the scale. This LUT compresses data in such a way that data from the shadows gets compressed less than data from the highlights."
In other words, if I understand the article, and don't presume I do, the Leica raw file has more information in the shadow areas than some. Expose at the native speed of 160 and you have the possibility of expanding the tone range of those dark images without them totally falling apart. It may do it better than some DSLRs, but there are limits. And those advantages will diminish as more cameras move to a 14-bit raw.
What does this mean in practical terms? When I'm on autopilot and my camera is on programmed auto exposure, I set the "film" speed down a notch, adjust the raw file as necessary and decrease my chances of blowing out the highlights to detail-less garbage.
My TTL meters on my DSLRs are always set to expose a third of a stop less than the conventional exposure. (With the M8, I've always reduced the exposure by two-thirds of a stop.) This parallels Kodak's old recommendation for transparency films where they suggested the third of a stop reduction for "professionals." Transparency films with their limited exposure latitude and the possibility of turning highlights into detail-less cellophane have always paralleled some of the characteristics of the digital camera image.
As to what to do the next time you're covering a demonstration/riot that gets out of hand and you want to increase your exposure latitude ... well, there are too many variables between cameras, TTL meters, image processing programs, etc., to come up with some fixed recommendation. If I can use the lowest "film" speeds on the camera and shoot raw, I set the M8 down a full two stops and my Canon 5Ds down a stop.
요는 조리개 우선 설정으로 촬영할 경우 노출을 한 스톱 정도 낮춰서 촬영한 다음에 DNG를 열어서 노출 보정을 하라는 것이다. 개인적으로 노출부족 사진을 보정할 경우 발생하는 깨짐 현상이 불만족스럽고, 무엇보다 슬라이드 필름과 같은 뚜렷한 대비를 즐기는 성격이라 기본적으로 -1 stop 세팅을 권하고 싶지 않다. (위에 사진들은 저 글을 읽고 -2/3 stop으로 사무실 건물을 돌아 다니며 촬영한 스냅인데 예시로 적합하지 못한 것 같아 괜히 미안하네...)