Tests of Digital Cameras and Accesories

1. Introduction

The internet contains both true information and myths. Some notes were true years ago but are no longer true due to technical progress yet such information is still available. Each owner of a new device thus asks these questions:

1. Is it necessary to set white balance?
2. Should I be afraid of high ISO?
3. How good are my neutral and graduated filters?

Time will pass and information on this page will become obsolete and no longer valid. We will therefore explain procedures for performing these test so that everybody can apply them to his/her equipment.

2. Equipment used

All tests were done with Nikon D850, some of them were compared to older Nikon D200. Tested filters are NiSi V6.

3. How was the photo done?

When a photographer looks at pictures created in past, he/she sometimes asks one of these two questions:

1. How did I manage to make such a good photo>
2. What did I do wrong to make the photo look so ugly?

We are interested what lens was used but also the values of ISO, aperture and shutter speed. In past a photographer had to write it to a notebook. In the digital age such servis is provided by the devices. The information is store in EXIF which is a topic of the next section.

4. What is EXIF?

EXIF is an abbreviation meaning Exchangable Image File Format. EXIF presents the very mechanism enabling storage of additional information together with the image data. They contain much more pieces of information than mentioned in the previous section and are stored not only by the digital cameras but also by mobile devices.

The EXIF format is not as standard as users would like. After the creation the specification ceased to be centrally maintained. The manufacturers were not able to store information which they would like to insert, therefore a lot of extensions appeared. In addition, information is usually stored as numerical codes and conversion tables are very long. Without a good software the information is unusable.

Programs for processing EXIF metadata differ in several aspects. From the user's point of view it is important whether it is a command-line tool or whether graphical interface is available. Some programs serve as viewers only, some programs can edit and insert information. And since manufacturers create their own extensions, it is also important to know, which of them are understood by the software.

Nowadays the graphical editors preserve the EXIF metadata including those not understood. It was not so in past end even now it is possible that metadata will be lost in some operation. It is therefore a good idea to store the original file because the EXIF metadata can be copied from it to the final file.

5. ExifTool

ExifTool is a program written in perl and must be used from a command line. The disadvantage is uncomfort of use. The advantages are that it is possible to execute an action on all files with a single command and that it is probably the most complete with respect to the manufacturers' additions.

Let's assume that you use a device which stores the positional data. Now you want to retrieve them from all files in the working directory a want to order the output according to the file names. You get this information by:

exiftool -a -gps:all -gpsposition -fileorder filename .

We have said that the EXIF metadata can be lost. Let's assume that the raw images were produced by a Nikon device hence the file name format is _dsc0123.nef. We have less than a thousand processed files with name of the form image123.jpg where the number corresponds to the number of the original raw file. The EXIF metadata of all JPG files in the working directory will be restored by:

exiftool -TagsFromFile _dsc0%-3f.nef -all:all -ext jpg .

%-3f says that only the last three characters before the dot of the JPG file name should be used thus replacing image with _dsc0.

The program exists as a package for all good Linux distributions and is available from MacPorts. For all other cases use information from ExifTool by Phil Harvey.

6. EXIF: a good servant but...

EXIF contains many pieces of information which serves us with image processing but can reveal what we want to hide. If you own a company, you probably wish your customers to find the way to you, you want to publish a list of products and services but do not like to provide them with access to your accounting system. It is the very same case with image metadata. Before publishing the images you should delete privacy metadata. Graphical programs do not always display all metadata, therefore I suggest the above mentioned ExifTool.

All metadata can be deleted from all images of the JPG format in the current directory by

exiftool -all= --icc_profile:all *.jpg

--icc_profile:all in the command above preserves the information on the colour profile which is important for correct display.

You can find detailed information on a potential risk in EXIF metadata privacy: A picture is worth a thousand data points.

7. What's inside the raw files>

The raw files contain two kinds of information, the image data and the metadata in the EXIF format. The contents depends on the camera used to acquire the picture. In addition to text fields, binary data are also present, for instance previews. The Nikon digital cameras insert:

1. Thumbnail TIFF: thumbnail in the TIFF format, dimensions 160x120
2. Preview Image: JPG preview, dimensions 640x424 for D850, 570x375 for D200
3. Other Image JPG preview, dimensions 1620x1080 for D850, unavailable for D200
4. JpgFromRaw: JPG preview in full resolution

The list of all preview images in file _dsc0001.nef can be displayed by:

exiftool -a -preview:all _dsc0001.nef

dimension of the Preview Image can be obtained by extracting it using the -b option and displaying the dimensions by subsequent invocation of ExifTool:

exiftool -b -PreviewImage _dsc0001.nef | exiftool -ImageSize -

POSIX-compliant systems allow us to retrieve the types and dimensions of all previews by a single long command:

img=_dsc0001.nef
for a in `exiftool -preview:all "$img" | sed 's/ //g' | awk -F: '{print $1}'`
do echo $a
exiftool -b -$a "$img" | exiftool  -imagesize -
done

It can be entered on a single line if the parts are separated by semicolons.

The examples shown in the tests are mostly previews of type Preview Image. We extracted them from the EXIF metadata to a subdirectory named subdir. The command was:

exiftool -b -PreviewImage -W subdir/%f.%s -ext nef .

If we needed a preview of a different type, we used -OtherImage or -JpgFromRaw, respectively.

8. Technical notes

The tests contain illustration and comparison images. If there are many images, the only possibility is to show of them. If just two images are presented for comparison, it is more useful to make use of a before/after slider. Several solutions are available from the web. I refused the commercial ones and the decision seems to be correct. Many plugins work fine with images supplied with the samples but cease to work if I replace them with mine, they get distorted and I did not manage to find out what has to be changed in order to make them work. In addition, the plugins come with long, complex cascaded stylesheets which are not easy to integrate into my pages, total destruction of the contents was a frequent result. Finally I found a simple solution which satisfies my needs and works in my pages without the necessity of changing anything. The solution is BeerSlider.

9. Detailed tests

All tests contain images and information extracted from them by ExifTool. The command is always given in the test. This is the list of the tests:

1. How Important Is Correct Setting of White Balance?
2. Effect of ISO on Digital Noise
3. Neutral and Graduated Filters NiSi
4. Circular Polarization Filter