With lensTESTER you now have the possibility to evaluate different quality characteristics of your camera equipment at home.
Photography allows the capturing of reality, altering that reality or sharing a special moment with other people. However, what makes an image a good image? On the artistic side, opinions about an image can be much divided. Some shots captivate us, create emotions or reflect them impressively. Whether good or bad, evaluation lies in the eye of the beholder.
However, the creative aspect is not the only one that influences evaluation. Image quality also plays an important role. Blurred, weakly resolved or noisy images are usually unwanted, because they can negatively influence the impression of a photo. For this reason, the camera equipment underlies various requirements, as image quality is the foundation of a good photo.
The focus is on resolution and contrast behavior. Consisting of a high-quality test chart and an online-based analysis, diverse camera-lens combinations can be easily tested and analyzed at any time. The poster and its related sub charts can be attached to a free wall surface, in the living room for example, and allows taking different test series with little effort.
lensTESTER enables you to
- check how well the resolution of your camera-lens combination performs over the image field
- test the centering of your lens.
- evaluate resolution over different aperture settings
- take multiple images in an autofocus series, to evaluate autofocus accuracy
- measure image quality loss depending on the ISO setting used
In addition, you can of course experiment with your camera settings to get results on often-used settings like contrast or sharpness corrections. Customers who choose a premium membership will also have the opportunity to compare their results with each other and in future with different camera-lens combinations from other users.
Why the poster format is set to A0
The market offers a wide range of camera models. The sensor is a base component and can vary in size and pixel number. To ensure that the test chart complies with the requirements of various megapixel sensors, appropriately designed siemens stars are required for resolution measurement. The size of the chart, the amount of black-white alterations in a siemens star and the size of the central marker, define which megapixel range the test chart is designed for.
If it would be suitable for cameras with 3 to 30 megapixel only, for example, devices with higher or lower maximum resolution would not produce consistent measurement results. These calculated results would not allow for a comprehensive evaluation of image quality.
lensTESTER is developed for cameras from 6 to 70 megapixel. A poster in A0 format is required for this kind of compatibility.
Color deviations between poster and sub charts
You probably noticed a slight deviation in color between the test chart and the single chart elements. The reason for this can be explained by the different manufacturing processes of individual product components. Photographic paper had to be used in the production process in order to accurately implement those very thin line pairs of the siemens stars in full detail. When you take a closer look at the center of a siemens star, you can clearly distinguished the lines from each other, all the way to the center marker. It is this precision in production that makes a meaningful analysis possible.
Certainly the exposure on photographic paper is quiet expensive and producing the whole poster that way would have definately increased costs. To keep lensTESTER and the related analysis affordable for everybody, we decided to pursue a compromise. Ensuring a professional level analysis, the single test elements are produced on photographic paper. Visual elements like the background and gridlines have no influence on the analysis, so we choose the less expensive offset printing process for poster production. The difference in production processes cause a small deviation, that is still within the range of tolerance.
What the siemens stars are needed for
Siemens stars are utilized to calculate contrast behavior and resolution. The test pattern contains alternating white and black segments, that become narrower approaching the center. The number of black-white changes (line pairs) per millimeter or pixel is called spatial frequency.
For calculating resolution, a siemens star is captured by a recording system. In an ideal szenario the recorded image would completely correspond to the original. In reality, when spatial frequency increases, contrast decreases. That means, the finer the line pairs become, the more the contrast tends to decrease. If the contrast drops below 10%, two line pairs cannot be distinguished from each other clearly enough any more. The resolution, that is given at this threshold, is termed as limiting resolution, the maximum reachable resolution of a camera-lens-system.
Because the test chart contains harmonic siemens stars, the transitions between light and dark lines are smooth (sinusoidal). The reason: direct transition from black to white will lead to in-camera sharpening. To avoid camera internal sharpening, the siemens stars transitions from black to white need to be harmonic.
lensTESTER supports JPG and TIFF images
For test image evaluation, we deliberately have chosen JPG and TIFF format.
There are different ways JPGs can be generated. On one hand the JPG format is a factory default setting of most cameras today and captured images are based on camera internal processing of raw data that reflect the cameras characteristics. On the other hand photographers can convert RAW data into JPG files by using a picture editing program. Thus evaluation of image quality is barely affected by internal image optimizations of the camera.
In general, the JPG format contains different data compression methods. Compression does not automatically lead to high quality loss. Depending on the compression method chosen, the loss of overall image quality varies.
Many cameras offer different compression levels in the form of quality settings, like "Fine" or "Normal". If high quality is selected, data reduction and the associated loss of data is small. The lower the image quality is set to, the stronger the image is compressed. Because of low capacity storage media at the beginning of digital photography, higher compression allowed saving more images on the same memory card. Through technical evolution, memory cards offer much more capacity now. Thus, a low compression/high image quality can be chosen.
Besides JPG files, the analysis of 8-bit / 16-bit TIFF images is supported.
In principle we do not exclude the RAW format. Raw data does not have an explicit relation to white balance, color, brightness and other parameters. It only includes basic information and has to be converted to a corresponding image format for analysis. There are different picture editing tools, that allow to convert RAW images into a common file format (.tif, .jpg). In addition to the assignment to a color space, different attributes, like tonal value or sharpness, can be adjusted.
Why choosing JPG
A qualitative evaluation and comparison of RAW converted test images is quite difficult, because results depend on the art and form the RAW images were converted. To give a genuine statement on image quality, RAW data should be transformed nearly unedited into JPG Format (sRGB) using “high quality compression”. Thus data loss is kept very small and image quality hardly differs from a created TIFF format. For illustration we take a test image which was shot in RAW. To compare the image quality, we focus on the central Siemens star.
You can download the images here
The first image was converted into a JPG file using “high quality compression”. The second image was exported as lossless 8-Bit TIFF format. As you can see, the reproduction of fine details is nearly identical. Also the analyzed results barely differ from each other. According to the Nyquist frequency of the camera both images reach about 83,6% (center) of the possible resolution, proving that JPG converted images can deliver TIFF quality. High quality loss between TIFF and JPG is not to be expected, as long as JPG compression is set to "high quality" or 100%. Moreover, the smaller jpg file size is more advantageous in relation to the upload of your images.
To analyze RAW data, we kindly ask you to convert it into JPG (TIFF) format. Please avoid image editing and choose sRBG colorspace and “high quality compression” for JPG image processing. These requirement are the key to a good evaluation of image quality.