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12. How to extract pixel values from images
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**RSP Aspect:** Portal

**Contact authors:** Yumi Choi

**Last verified to run:** 2025-03-05

**Targeted learning level:** beginner 

**Introduction:**
This tutorial demonstrates how to extract pixel values from active images retreived from a Portal image query.

**1. Execute an image query.**
Go to `data.lsst.cloud <https://data.lsst.cloud>`_ , select the Portal Aspect, and
click on the "DP0.2 Images" tab at the top. Enter your desired constraints for the image query,
and click "Search" to execute it.       

**2. Select the Line Tool.**
To extract pixel values along a line (1D brightness profile),
click the "Tools" icon, then select the "Line" icon under the "Extract" section.
In the instruction window, choose an aperture for combining values.

**3. Draw and view profile.**
Click the starting point on the image, drag to the endpoint, and release. 
A pop-up window will display the 1D brightness profile, where you can adjust the aperture if needed.

**4. Save or download.**
Click "Pin Chart/Table" to add the chart and table to the result,
or download them directly. Repeat the process to extract another profile.

.. figure:: /_static/portal_tut06_step03a.png
    :width: 500
    :name: portal_howto_image_extract_pixelvalues-1
    :alt: A screenshot displaying a line drawn across a source, accompanied by a pop-up window showing the source's 1D brightness profile along that line. 

    Figure 1: A line drawn across a source, with a pop-up window displaying the 1D brightness profile of the source.

                                        
**5. Select the Points Tool.**
To extract pixel information for selected points,
click the "Points" icon under the "Extract" section. 
In the instruction window, choose an aperture to combine the values. 

**6. Select points.** 
Click multiple points on the image to extract their pixel values at once. 

**7. Save or download.**
Click "Pin Chart/Table" to save the results temporariliy, or use "Download as Table" and/or
"Download Chart" to save them locally. Results can also be saved as a DS9 region file. 

.. figure:: /_static/portal_tut06_step03b.png
    :name: portal_howto_image_extract_pixelvalues-2
    :alt: A screenshot displaying six selected points on the image (left panel), in the active chart (right panel), and in the pinned table (bottom panel), with a pop-up window offering options for file format and naming for saving.

    Figure 2: Six selected points on the image (left panel), in the active chart (right panel), and in the pinned table (bottom panel), with a pop-up window offering options for file format and naming for saving.


Return to the list of DP0.2 :ref:`DP0-2-Tutorials-Portal`.