Keywords: Graphics, Image Processing, Color Science, RGB, Grayscale

Documents

Texture Formats

Texture formats
http://wiki.polycount.com/wiki/Texture_formats

Grayscale

Grayscale
https://en.wikipedia.org/wiki/Grayscale

Converting RGB to grayscale/intensity
https://stackoverflow.com/questions/687261/converting-rgb-to-grayscale-intensity

数字图像处理(18): 图像灰度变换——线性灰度变换 和 非线性灰度变换(对数变换 与 伽马变换)
https://blog.csdn.net/zaishuiyifangxym/article/details/89817995

Interpolation

Bicubic interpolation
https://en.wikipedia.org/wiki/Bicubic_interpolation

Cubic Hermite spline
https://en.wikipedia.org/wiki/Cubic_Hermite_spline

Applications

Grayscale

Q: How to compute grayscale in UE4 Materials?
A: The dot product of a RGB color and a coefficient is grayscale, this value can be used to computing falloff.

and you can get a new color with grayscale modified by appending these individual channels.

Panorama Stitching

Panorama Stitching using OpenCV Python
https://www.youtube.com/watch?v=8oFRmdDum5k

How To Make Panorama Images with Image Stitching in OpenCV Python
https://www.youtube.com/watch?v=Zs51cg4mb0k

Image Panorama Stitching with OpenCV
https://towardsdatascience.com/image-panorama-stitching-with-opencv-2402bde6b46c

How to create a panorama image using OpenCV with Python
http://datahacker.rs/005-how-to-create-a-panorama-image-using-opencv-with-python/

Image Stitching with OpenCV and Python
https://www.pyimagesearch.com/2018/12/17/image-stitching-with-opencv-and-python/

OpenCV panorama stitching
https://www.pyimagesearch.com/2016/01/11/opencv-panorama-stitching/

Ordinary Tricks on OpenCV-Python

How do I access the pixels of an image using OpenCV-Python?
import cv2
image = cv2.imread("sample.jpg")
pixel= image[200, 550]
print pixel

output:

[ 73 89 102]

pixel_b, pixel_g, pixel_r = image[row][column]

Origin:
https://stackoverflow.com/a/38202214/1645289

Add an alpha channel to a image

Python opencv adds an alpha channel to the image and sets the transparency:

import cv2
import numpy as np

img = cv2.imread("/home/shuai/Desktop/lena.jpg")

b_channel, g_channel, r_channel = cv2.split(img)

alpha_channel = np.ones(b_channel.shape, dtype=b_channel.dtype) * 255
#minimum is 0
alpha_channel[:, :int(b_channel.shape[0] / 2)] = 100

img_BGRA = cv2.merge((b_channel, g_channel, r_channel, alpha_channel))

cv2.imwrite("lena.png", img_BGRA)

Origin:
https://www.programmersought.com/article/5735956225/

Python with OpenCV3

# First create the image with alpha channel
rgba = cv2.cvtColor(rgb_data, cv2.COLOR_RGB2RGBA)

# Then assign the mask to the last channel of the image
rgba[:, :, 3] = alpha_data

C++

# First create the image with alpha channel
cv::cvtColor(rgb_data, rgba , cv::COLOR_RGB2RGBA);

# Split the image for access to alpha channel
std::vector<cv::Mat>channels(4);
cv::split(rgba, channels);

# Assign the mask to the last channel of the image
channels[3] = alpha_data;

# Finally concat channels for rgba image
cv::merge(channels, 4, rgba);

Origin:
https://stackoverflow.com/a/50159769

Get alpha channel of a image
dir_of_script =  pathlib.Path(__file__).parent.absolute()
full_path = os.path.join(dir_of_script, "heightmap.png")
image = cv2.imread(full_path, cv2.IMREAD_UNCHANGED)
#(400, 250) is just pixel postion for testing
pixel = image[400, 250]
# would print 4 channels
print(pixel)

Output:

[  0   0   0 118]

Reference:
https://stackoverflow.com/a/36452596/1645289

Create transparent image in opencv python
import numpy as np
import cv2

img_height, img_width = 300, 300
n_channels = 4
transparent_img = np.zeros((img_height, img_width, n_channels), dtype=np.uint8)

# Save the image for visualization
cv2.imwrite("./transparent_img.png", transparent_img)

Reference:
https://stackoverflow.com/a/44595221/1645289

Then he made one last effort to search in his heart for the place where his affection had rotted away, and he could not find it. ― Gabriel Garcia Marquez, One Hundred Years of Solitude