pixel_math.md 1.75 KB
 Christian Tischer committed May 28, 2019 1 2 3 4 5 6 7 8 9 10 11 12 13 14 15 16 17 18 19 20 21 22 23 24 25 26 27 28 29 30 31 32 33 34 35 36 37 38 39 40 41 42 43 44 45 46 47 48 49 50 51 52 53 54 55 56 57 58 59 ``````--- title: Image math layout: page --- ## Image math ### Activity: Pixel based background subtraction * Open image: xy_8bit__nuclei_noisy_different_intensity.tif * Appreciate the significant background intensity * Measure pixel values at `[ 28, 35 ]` and `[ 28, 39 ]` * Measure the image background intensity in this region: * upper left corner at `[ 20, 35 ]` * width = 10 * height = 10 * Subtract the measured background intensity from each pixel. * Measure the pixel values again. * Observe that the resuls are incorrect. Repeat above activity, but: * After opening the image, convert its data type to floating point. ### Activity: Explore the limitations of `float` data type * Create an empty image * Set all pixel values to 1000000000.0 * Add 1.0 to all pixel values * Be shocked... ...it turns out that from 16777216 on you cannot represent all integers anymore within a float. ### Formative Assessment True or false? * Subtracting 100 from 50 in a 8-bit image will result in -50. * Adding 1 to 255 in a 8-bit image will result in 256. * Subtracting 10.1 from 10.0 in a float image will result in -0.1 * Adding 1.0 to 255.0 in a float image will result in 256.0 * Adding 1000.0 to 1000000000.0 in a float image will result in 1000001000.0 ### Learn more * [Limitations of float](https://randomascii.wordpress.com/2012/02/13/dont-store-that-in-a-float/) ``````