Reading Image as Color or GrayScale Image in Python using OpenCV - Machine Learning Tutorials, Courses and Certifications (2024)

FAQs

How to read grayscale image in OpenCV Python? ›

To convert an RGB image to grayscale using OpenCV, we can use the cv2. cvtColor() function and specify the conversion code as cv2. COLOR_BGR2GRAY. This will convert the image to grayscale and return a single-channel image.

PIL is a popular library used for image manipulation and processing in Python. To convert a grayscale image to color, we can use the PIL ImageOps module's colorize function, which applies a color tint to a grayscale image based on the specified color and intensity values.

In the above code, cv2. imread() function is used to read the image in color mode and store it in the input_image variable. Then, the cv2. split() function is used to split the image into its three color channels (blue, green, and red), which are stored in blue, green, and red variables respectively.

It helps in simplifying algorithms and as well eliminates the complexities related to computational requirements. It makes room for easier learning for those who are new to image processing. This is because grayscale compressors an image to its barest minimum pixel. It enhances easy visualisation.

Displaying Grayscale image

Now open the image using PIL image method and convert it to L mode If you have an L mode image, that means it is a single-channel image – normally interpreted as grayscale. It only stores a grayscale, not color. Plotting the image as cmap = 'gray' converts the colors.

The RGB values are converted to grayscale using the NTSC formula: 0.299 ∙ Red + 0.587 ∙ Green + 0.114 ∙ Blue. This formula closely represents the average person's relative perception of the brightness of red, green, and blue light.

Simply do print(img. shape) and see how its output is. If it's like something (256,256,3) then it's an RGB image where 3 represents 3 channels. But if it's something like (256,256) then it's a grayscale image.

The image should be in the working directory or a full path of image should be given. By default, OpenCV stores colored images in BGR(Blue Green and Red) format.

How to read an image in grayscale? ›

Method 1: Using imread() function

So to convert the color image to grayscale we will be usingcv2. imread("image-name. png",0)or you can also writecv2. IMREAD_GRAYSCALEin the place of 0 as it also denotes the same constant.

We use cv2. threshold() to convert a grayscale image to binary image. To convert a color image to binary image, we first convert the color image to grayscale image using cv2. cvtColor() then apply cv2.