Measure lens vignetting and sensor nonuniformity
Flat Field measures lens vignetting (dropoff in illumination at the edges of the image) and other image nonuniformities. For example it can measure the evenness of flash illumination (using light bounced off a white wall) or the uniformity of flatbed scanners. In Imatest, Flat Field can also analyze color shading (nonuniformity), hot and dead pixels, display a pixel level histogram, a grid (sector) plot, and a detailed image of fine nonuniformities (i.e., sensor noise). These features are described in Using Flat Field, Part 2.
Flat Field Interactive is the interactive equivalent of Flatfield. Use it when you want to examine an image in detail.
Partial support for the EMVA-1288 standard (temporal noise and spatial nonuniformities) is included in Imatest 2020.2. More details.
This page describes Flat Field (formerly Uniformity ) features available with Imatest Master. Flat Field was originally intended to measure lens vignetting (the falloff in illumination at the edges of the image), but it has been enhanced to measure a variety of image nonuniformities— resulting from the lens, illumination, or sensor— including color shading, noise distribution, and spots from dust (though Blemish Detect is much better at handling visible spots). Basic instructions are found in Using Flat Field, Part 1.
Input settings - Results - Hot & Dead pixels - Optical center - Color shading - Profiles - Grid plot
Grid contour map - Histograms - Noise detail - Spot detection
Where to go next
- Running flat-field analysis: preparing the image, running it from either interface, and every setting that controls it.
- Flat Field results: the contour plots, uniformity profiles, histograms, noise detail and the output files.
- Blemish Detect: finding visible sensor defects in a flat-field image.
- Flatfield INI reference: the settings as stored in the INI file.
Links
Vignetting by Paul van Walree, who has excellent descriptions of several of the lens (Seidel) aberrations and other causes of optical degradation.