Einstein considered the case of isotropic radiation of frequency and spectral energy density . However, spatial resolution is a factor in addition to spectral resolution. More precise measurements can be obtained through acoustic analysis of a spectrogram or spectral slice. Infrared radiation is divided into spectral subregions. Newer missions have higher spectral and spatial resolutions. This color is an approximation of an orangish red spectral color. Stars are classified as supergiants on the basis of their spectral luminosity class. More generally there are various other methods of spectral estimation. It is one of a number of approaches to spectral density estimation. This offers the possibility to combine spectral identification with imaging. Colored objects are perceived differently under light sources with differing spectral distributions. Such insight can be useful in improving some algorithms on graphs such as spectral clustering. In astronomy, stellar classification is the classification of stars based on their spectral characteristics. Some monochromators have several gratings that can be selected for use in different spectral regions. Each formed cluster can be diagnosed using techniques such as spectral analysis.