My camera says snow is gray color – a beginners guide to camera's in-built metering

My cousin recently came back from Kashmir and Simla annual vacation. Needless to say, armed with the latest digital camera, she came back with tons of pictures and was excited to show them to us.

I had seen pictures of Kashmir in magazines and television with it's snow capped mountain peaks, beautiful landscapes covered with snow, children playing in white fluffy snow, and pristine crystal clear rivers cutting through the landscape!!!!

I was quite disappointed when I saw the pictures that were taken during the vacation. It presented quite a different story to what I was expecting. The pictures were dull, colors did not look right, and lacked that “punch” in them.

My cousin, determined to impress everyone with the pictures, immediately started her favorite photo editing program and started fidgeting with levels, brightness, contrast and other functions of a modern day post processing tools. She clearly was relying on visual changes that were happening on her monitor to decide that pictures to look as good as the scene she had seen.

After updating 150+ pictures and spending close to 20 hours in front of the computer salvaging the pictures, she asked me why this happened and if there was something wrong with the camera.

She asked me a few questions:

“Why did the snow look gray in pictures and not white as it was actually.” “Why did the black color wooden cottage look gray and not near to black”

I explained to her that this was due to how “your camera's meter” saw the snow and determined the amount of light needed to expose it correctly versus what you “thought” it saw and registered.

Camera's in-built meter are designed to work with “reflected light” off the scene (majority of them). The design takes some assumption that all subjects are average color and will reflect average light off the subject to meter and there will be more then one color in the frame. This assumption works in most cases as normally you will have shades of multiple colors in a scene. This gives you near to correct exposure.

Things get tricky when you have dominance of one color in a scene. Meter gets fooled in believing that there is too much or too little light and result is over or under exposure.

Most noticeable are the whites and blacks as our eyes are trained to see black as pure black and white as pure white. We can very easily make out if white or black color is not looking like what it did when you shot the scene.

I shared a simple trick with her that my father shared with me when I was very new to photography. "In order to get correct exposure, over expose by a stop or two when shooting white subjects and under expose by a stop or two when shooting black subjects."

She clearly looked confused, so I did a little experiment to explain her what I was trying to say. I tried to replicate the environment in which she took pictures by using “near to white” and “near to black” subjects and shooting them individually on same color background.

Here is the test setup and settings:

White Subjects:
1) 3 to 4 mint capsules
2) iPod docking station
3) white paper with a white cloth for base material on which subjects were placed

Black Subjects:
1) My phone
2) Ear phones
3) black cloth for base material on which subjects were placed

Camera settings:
1) Canon 350D with 18-55mm lens (Tripod Mounted)
2) Focal length: 35mm
3) Aperture (Av): f/8
4) ISO: 100
5) Camera to subject angle: 30 – 45 degrees
6) Metering Mode: Evaluative (as this is the default in most cameras)
7) White Balance: Auto

Post processing:
1) RAW to JPG Conversion using UFRaw
2) Resized images using GIMP batch processing


White Subject: Test results & Observations:

Image 1: Exposure as per camera's in-built meter Shutter Speed (Tv): 1/30s
Heavily under exposed

This picture turned out to be pretty dull and clearly under exposed. This shows that the camera meter did not understand that the subject itself is white and it need not reduce the light reaching the sensor. In this case, since the frame is filled with white subject, meter thinks that there is too much light in the frame and sends less of it to the sensor thinking that it is avoiding over exposure.

In order to get the desired results, I started moving away from the suggested exposure as per the meter. Since it is white subject and meter is under exposing (sending less light to sensor), I intentionally started over exposing (sending more light to sensor).

I increased the exposure by 1 stop and 1/3rd stops thereafter to get the following results.

Image 2: Meter +1 stop Shutter Speed (Tv): 1/15s
Better than metered, but still under exposed

Image 3: Shutter Speed (Tv): 1/13s
Correct exposure very near to what was seen by eye
Image 4: Shutter Speed (Tv): 1/10s
Over exposure seen in some areas

Image 5: Meter +2 stops Shutter Speed (Tv): 1/8s
Over exposure seen in most areas
Observation:
While shooting white / near to white subjects, over exposing between +1 and +1 ½ stops, I got accurate reproduction of lighting and colors. Image # 3 above is correct exposure for this test.

Moment I reached near the +2 mark, over exposure was seen and I lost details in the subject.

Black Subject: Test results & Observations:

Image 1: Exposure as per camera's in-built meter Shutter Speed (Tv): 1/4s
Over exposure seen in most areas - black is looking washed out and more towards gray



This picture turned out to be clearly over exposed. This shows that the camera meter did not understand that the subject itself is black and it need not increase the light reaching the sensor. In this case, since the frame is filled with black subject, meter thinks that there is way too less light in the frame and sends more light to the sensor thinking that it is avoiding under exposure.

In order to get the desired results, I started moving away from the suggested exposure as per the meter. Since it is black subject and meter is over exposing (sending more light to sensor), I intentionally started under exposing (sending less light to sensor).

I reduced the exposure by 1 stop and 1/3rd stops thereafter to get the following results.

Image 2: Meter -1 stop Shutter Speed (Tv): 1/8s
Black is seen as near to black




Image 3: Shutter Speed (Tv): 1/10s
Black is seen as near to black - little more improvement from earlier shot




Image 4: Shutter Speed (Tv): 1/13s
Perfect exposure - black is looking pure black as seen by eye



Image 5: Meter +2 stops Shutter Speed (Tv): 1/15s
Black is seen as black, but we start loosing details in subject



Observation:
While shooting black / near to black subjects, under exposing between -1 and -1 ½ stops, I got accurate reproduction of lighting and colors. Image #4 is the correct exposure for this test.

Moment I reached near the -2 mark, under exposure was seen and I lost details in the subject.

Conclusion:
Metering is a tricky subject and mastering it will take some study and lot of practice for all of us. I hope with this post, I have cleared some basic doubts of how in-built meters work and some simple ways in which we can avoid under and over exposure.

Do share if you have any tips or suggestions on this topic.

Other related readings:
http://www.kodak.com/cluster/global/en/consumer/products/techInfo/af9/index.shtml