Learning ObjectivesAfter completing this lesson, learners should be able to:
Examine the values of pixels in an image.
Images are very often composed of pixels. Pixel stands for “picture element”. In 3-D, a pixel is sometimes also called a voxel, which stands for “volume element”. To analyse images it is very important to know how to examine the pixels (voxels) in an image.
Explore the values, indices (and sizes) of pixels in an image.Show activity for:
Explore pixel values and indices
- Open image: xy_8bit__nuclei_noisy_different_intensity.tif
- Explore different ways to inspect pixel values and indices
- Check where the lowest pixel indices are in the displayed image: * Most commonly: Upper left corner, which is different to conventional coordinate systems.
Explore pixel sizes
- Open image: xyz_8bit_calibrated_anisotropic__mri_head.tif
- Check the pixel sizes (calibration) of this image
- Explore how image calibration affects spatial measurements, e.g.,
- Measure the distance between two pixels in the image
- Measure the size of an image region
- Appreciate that image calibration might be neccessary, e.g.
- 3D distance measurements
- Appreciate that image calibration can be confusing, e.g.
- not consistently used in image filter parameter specification
True or false? * The lowest pixel index of a 2D image always is
[1,1]. * When looking at a 2D image, the lowest pixel indices are always in the lower left corner.
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