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Taking Photographs

(10 - End of this Evolution - Image PROBLEMS)or Back to Table of Contents

Evaluation:

We looked at how to technically photograph images and then artistically compose them. Now some post production checks on how to look for technical problems after downloading the images. On all web sites that share images there are people who complain about the photographs of others. Since images are about telling a story it's really up to the photographer if the image tells his or her story. When it comes to the technical part one could say that It's hard to know if there is truly a perfect image out there. This is because of the amount of issues that can go wrong in the process of taking the image. Evaluating the image after you taken it requires very objective and cold eyes. By cold I mean you have to distance yourself from the emotions regarding the subject in the image. Images are a powerful medium. Assuming you have met your goal of getting the image you desired someone could still come along and talk negatively about your image. This is because many problems occur when images are taken due to how cameras work in general. Here are the most common problems you encounter when you download your images from your digital camera. If you are aware of these problems you can minimize them as you take the photograph.

EXPOSURE PROBLEMS:

We've already covered exposure problems in the previous pages. Exposure problems can be minimized by checking the histogram during shooting. By now you are probably all too aware that proper exposure is the cornerstone to getting a good image. No camera can do this by themselves and the photographer has to monitor this. Basically if the digital data is intact and the histogram looks great then you can also assure it's possible to fix many of the image woes in post processing any time later. Many times new cameras will blink on the LCD preview of the camera in the over exposed white areas where the information has been "blown out" and is totally white. If this isn't an intentional artistic effect then working to get the exposure correct is worth the goal.

It's true that over-exposure may be obvious by the histogram. However, sometimes using a graphics program to lower the "gamma" all the way down to dark leaves only these blown out areas remaining. On occasion one sees the blown out areas and when the gamma (brightness and contrast button in one) are lowered one finds the blown out areas were not where they believed them to be. For instance the face did have detail and something unimportant in the background was unsalvageable.

The image on the left is good but the image on the right above illustrates over-exposed in the bright blown out areas

NOISE PROBLEMS:

Digital image noise occurs when you are photographing in low light situations and using a high ISO. In my example below this is such a case. I took this image at 1600 ISO and from across a concert hall using a 1000mm lens. The reason for the high ISO in my mind was trying to minimize the motion blur of the musicians. This particular camera didn't have a very high ISO level. Noise is more common in some cameras than others. A very hot camera will add noise to the image as well. That's because the circuitry will contribute noise in these warm situations. However, programs exist to remove digital noise. Programs like 'Noise Ninja' work great as plug-ins to Photoshop. While the final results of such noise removing programs can have a very surreal or 'painting' like smoothness, they beat the rough look of too much noise in most cases. Lastly if you are savvy enough then your camera may have additional features to help out with this problem. The Canon XSI has a custom function deep in the menus for Eliminating Noise Caused by Higher ISO Sensitivities. Like everything in photography, there are times when noise will be artsy and desirable to give your image a more grainy effect. You'll want to choose when and how noise is acceptable.

White balance is the next problem and usually due to how your camera produces colors. All camera manufacturers have different hardware and math for processing images. Therefore, the same scene can take on many different shades of colors depending on the camera. Most camera's white balance these days are pretty darn good. However, sit back and look at the thumbnails of the images before you process them. Often you see a tint to the image and this is a clue the white balance is incorrect. On the example below the icey river looked fine. Upon closer inspection the white balance was significantly off and a blue tint was present. After the image was color corrected it appeared as it did on location with the warm orange sun reflection in the valley.

Left is the blue image out of the camera no wb and right is the color corrected version

Right is the yellowish image out of the camera no wb and left is the color corrected version

COLOR PROBLEMS:

The other main color problem one encounters is chromatic aberration. Chromatic aberration is where lenses focus different wavelengths of light but not all those wavelengths land on the next lens or the sensor in the desired location. A lens is a bit opposite of a prism where the goal of the lens is to avoid having the light spread out like a rainbow. For instance, the red wavelengths are a tiny bit displaced when they land on the next lens. You then see a purple fringe. The wider lenses have to bend a great deal of more light into the sensor they are the most susceptible. Usually this happens on the edge of the image due to the bend or curve of the lens occurring more there. Even with wide angle lenses the problem usually shows up in a high contrast scene such as edges against a very bright sky. Many Photoshop tutorials have figured out ways to fix this in post processing. If you have an expensive lens you'll probably not see any chromatic aberration.

Purple fringe (chromatic aberration) on the sleeve of the shirt

COMPRESSION PROBLEMS:

Compression problems are usually created by the owner of the image after processing. The amount of colors in your image will often drive how large an image is before compression. JPEG images are compressed by most systems up to 75% by default. When saving images most programs ask you what compression level to use. If you up this at 100% your image will look terrific but take up much more space in computer storage. If you compress the image below 75% then unsightly artifacts show in the image as seen below. The goal when compressing is to leave the image with little visual artifacts while getting it as large as possible depending upon the purpose of your image. Try leaving the image of a reasonably large size while changing the compression to only 90%. Simply the smallest amount of compression reduces the overall file size greatly.

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Written Sept08 and updated Dec09 by - Tracy Lee Rose