How to use the command 'ppmcie' (with examples)
The ppmcie command is a powerful tool used to draw a CIE color chart as a PPM (Portable Pixmap) image. The CIE color chart is instrumental for understanding human color perception and is extensively used by professionals in the field of color science, imaging, and vision research. The tool allows users to visualize colorimetry and analyze various color systems and illuminants, thereby enabling advanced study and application in image processing, display technologies, and photometry.
Use case 1: Draw a CIE color chart using the REC709 color system as a PPM image.
Code:
ppmcie > path/to/output.ppm
Motivation:
This basic use case is particularly useful for individuals who want to generate a standard CIE color chart using the REC709, also known as ITU-R BT.709, color space which is widely adopted in high-definition television production. By simply executing this command, users can obtain a visual representation of this color space conveniently stored in a PPM image file.
Explanation:
ppmcie: Calls the command to generate a CIE color chart.>: Redirects the output to a file.path/to/output.ppm: A user-defined file path where the generated PPM image will be saved.
Example output:
The output will be a PPM image file displaying the CIE 1931 chromaticity diagram, illustrating the gamut of visible colors according to the REC709 color space. The diagram will show a horseshoe-shaped spectrum with RGB color points marked and the range of colors producible within this space.
Use case 2: Specify the color system to be used
Code:
ppmcie -cie -ebu -hdtv -ntsc -smpte > path/to/output.ppm
Motivation:
This use case is ideal for researchers and professionals who need to compare and analyze different color systems. By specifying various color systems such as CIE, EBU, HDTV, NTSC, and SMPTE, users can generate color charts that reflect these standards, aiding in studies related to color encoding, transmission, and reproduction in various media formats.
Explanation:
-cie|ebu|hdtv|ntsc|smpte: These options specify the color system to be represented on the CIE chart:-cie: Refers to the original CIE 1931 color system.-ebu: European Broadcasting Union color system.-hdtv: High Definition Television color system, the same as REC709.-ntsc: National Television System Committee, used in North America.-smpte: Society of Motion Picture and Television Engineers standards.
>: Redirects the output to a file.path/to/output.ppm: A user-defined file path for the output image.
Example output:
This results in a PPM image that illustrates the specified color system’s gamut superimposed on the CIE 1931 chromaticity diagram. Each color system has its unique triangle of possible displayable colors, enabling users to visually compare how they differ in terms of color representation.
Use case 3: Specify the location of the individual illuminants
Code:
ppmcie -red xpos ypos -green xpos ypos -blue xpos ypos > path/to/output.ppm
Motivation:
Specifying the exact coordinates of individual illuminants (red, green, and blue) is crucial for custom applications where precision in color reproduction and analysis is needed. This capability allows researchers to modify and study the impact of different primary colors on the overall gamut of color spaces in experimental settings.
Explanation:
-red xpos ypos: Specifies x and y coordinates for the red illuminant.-green xpos ypos: Specifies x and y coordinates for the green illuminant.-blue xpos ypos: Specifies x and y coordinates for the blue illuminant.>: Redirects the output to a file.path/to/output.ppm: A user-defined file path for saving the image.
Example output:
In this use case, the generated PPM image will include the customized positions for the red, green, and blue vertices within the CIE diagram based on input coordinates. Users will see a modified Maxwell triangle reflecting their specified illuminants.
Use case 4: Do not dim the area outside the Maxwell triangle
Code:
ppmcie -full > path/to/output.ppm
Motivation:
When analyzing the entirety of the color space, users might want to see the unaffected areas outside the Maxwell triangle, which represents achievable color gamuts. This option is particularly beneficial for educational purposes or when a clear definition of the total visible spectrum is necessary, without the dimming that highlights only the gamut of reproducible colors.
Explanation:
-full: Ensures that the entire color chart is displayed without dimming the areas outside the Maxwell triangle, providing a complete view of color perception.>: Redirects the output to a file.path/to/output.ppm: A user-defined file path for the output image.
Example output:
The resulting PPM image will display an undimmed horseshoe shape of all visible colors extending past the Maxwell triangle, providing a comprehensive view of the CIE 1931 chromaticity chart with no dimming applied outside practical color gamuts.
Conclusion:
The ppmcie command provides a valuable set of tools for generating and studying CIE color charts. Whether used for basic visualization of standard color spaces, comparison of various color systems, experimentation with custom illuminants, or observing the complete color spectrum, ppmcie helps unleash the intricacies of color analysis in PPM image format. By understanding each of its functionalities, users can adapt their needs into insightful visual data for a wide range of applications in color science and technology.
