The image data of the Context Camera (CTX) of the Mars Reconnaissance Orbiter require a flat-field correction that is currently available as a plain text file in the Planetary Data System “Calib” folders for all CTX Enhanced Data Record releases or automatically implemented as part of the ctxcal application of the Integrated Software for Images and Spectrometers (ISIS). We noticed (a) differences between these two flat-fields and (b) residual edge darkening (vignetting) after applying ctxcal. This work examines in detail the edge-darkening effect over time and creates a new improved flat-field calibration file to be implemented into the ISIS ctxcal application as a new default. We introduce a method to quantify the vignetting effect and its residuals after regular ISIS calibration. With the old calibration, the amount of residual edge-darkening is about eight percent. We prove that the new calibration does remove the effect completely, does not introduce any artifacts and qualitatively and quantitatively validate newly calibrated images. Mosaics produced with images that have been calibrated with our new flatfield show immediately less striping issues, without the application of any standard mosaicking-related tone-matching techniques.

中文翻译：

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火星勘测轨道飞行器上下文相机更新了飞行中校准

火星勘测轨道飞行器的上下文相机 (CTX) 的图像数据需要进行平场校正，该校正目前在所有 CTX 增强数据记录版本的行星数据系统“Calib”文件夹中以纯文本文件形式提供，或自动实现为图像和光谱仪集成软件 (ISIS) 的 ctxcal 应用程序的一部分。我们注意到 (a) 这两个平场之间的差异以及 (b) 应用 ctxcal 后残留边缘变暗（渐晕）。这项工作详细检查了随时间变化的边缘变暗效应，并创建了一个新的改进的平场校准文件，该文件将作为新的默认值实施到 ISIS ctxcal 应用程序中。我们介绍了一种在常规 ISIS 校准后量化渐晕效应及其残差的方法。使用旧校准时，残留边缘变暗量约为百分之八。我们证明新的校准确实完全消除了影响，不会引入任何伪影，并且定性和定量地验证新校准的图像。使用我们的新平场校准的图像生成的马赛克立即显示出更少的条纹问题，而无需应用任何标准的马赛克相关色调匹配技术。