| Description: 12 to 8 bit compression algorithm (0-7) used to compress images from 12 to 8 bits. Whether this option is enabled is indicated by mess.mdis.comp12_8. The compression is implemented using one of eight lookup tables, which are optimized to the lower WAC CCD read noise and higher NAC read noise, light levels, and bias level (nominal or after inflight drift). |
| Namespace Id: mess | Steward: ppi | Class Name: MDIS | Type: ASCII_Integer |
| Minimum Value: -9223372036854775808 | Maximum Value: 9223372036854775807 | Minimum Characters: None | Maximum Characters: None |
| Unit of Measure Type: None | Default Unit Id: None | Attribute Concept: None | Conceptual Domain: INTEGER |
| Status: Active | Nillable: false | Pattern: None |
| Permissible Value(s) | Value | Value Meaning |
| | 0 | Low-noise hi-bias SNR proportional. Case: Either NAC or WAC, for nominal bias (all DNs greater than 12-bit 230). Formulation: Maps 12-bit DNs between bias and saturation into 8 bits, proportional to SNR. Information loss is spread evenly over dynamic range. Usage: Typical imaging with varied brightness. |
| | 1 | Low-noise hi-bias DN-weighted SNR proportional. Case: Low-noise (WAC) CCD, bias nominal (all DNs greater than 12-bit 230). Formulation: Maps 12 bits between bias and saturation into 8 bits proportional to sliding scale. Information is preferentially retained at the low DN end. Usage: Faint objects. Saturates at a DN of 3000. |
| | 2 | High-noise hi-bias DN-weighted SNR proportional. Case: High-noise (NAC) CCD, bias nominal (all DNs greater than 12-bit 230). Formulation: Maps 12 bits between bias and saturation into 8 bits proportional to sliding scale. Information is preferentially retained at the low DN end. Usage: B/W, mostly low brightness. |
| | 3 | Low-noise med-bias SNR proportional. Case: Either CCD, assuming bias has dropped tens DN (all DNs greater than 12-bit 180). Formulation: Maps 12-bit DNs between bias and saturation into 8 bits, proportional to SNR. Information loss is spread over dynamic range. Usage: Typical imaging, varied brightness. |
| | 4 | Low-noise med-bias DN-weighted SNR proportional. Case: Lo-noise (WAC) CCD, assuming bias has dropped tens DN (all DNs greater than 12-bit 180). Formulation: Maps 12 bits between bias and saturation into 8 bits proportional to sliding scale. Information retained at low DN end. Usage: Faint objects. Saturates at a DN of 3000. |
| | 5 | High-noise med-bias DN-weighted SNR proportional. Case: High-noise (NAC) CCD, assuming bias has dropped tens DN (all DNs greater than 12-bit 180). Formulation: Maps 12 bits between bias and saturation into 8 bits proportional to sliding scale. Information is retained preferentially at the low end of the DN range. Usage: B/W, mostly low brightness. |
| | 6 | Zero-bias SNR proportional. Case: Contingency; assuming bias decreased to near 0 from the nominal 230 12-bit DNs. Formulation: Maps 12-bit DNs between bias and saturation into 8 bits, proportional to SNR. Information loss is spread over the dynamic range. Usage: Typical imaging, varied brightness. |
| | 7 | Linear. Case: either CCD, bias or read noise. Formulation: Maps 12-bit DNs between the bias level and saturation linearly into 8-bit space. Usage: High brightness mapping; information loss greatest at low DNs, preserves information at high DNs. |