Problem in Calculating NDVI Values Using Multispectral Images

I want to calculate NDVI values using multispectral images that range from -1 to 1 using the formula (NIR-R)/(NIR+R). NIR means the image in Near-Infrared band and R means the image in Red band. I apologize if there is any mistake and I humbly ask for guidance.

Following is the images in RGB, Red, and Near-Infrared that I have converted to jpg so I could upload it here, the original type is TIF.

Below is the code that I used to compute these images :

R = imread('RED.TIF');
NIR = imread('NIR.TIF');
NDVI = (NIR-R) ./ (NIR + R);  % [In this step I couldn't use / to compute, could you tell me why?]
NDVI = double(NDVI); % [Why the variable has to be changed to double type? Because if not the image couldn't be shown.]

colormap(jet); colorbar; impixelinfo;

Why is the NDVI variable only contain 0s and 1s? As the NDVI value should be ranging from -1 to 1 and I want the value to be in 2 digits after decimal. How can I improve the image processing as the green area of plants is missing in the final results? Do I need another methods to calculate it?

Thank you for your attention, sir.

[kazeem]

thank you, but the raster has so much misalignment. why?

Answer 1

[Image Analyst]

You need to cast to double before adding, subtracting, or dividing

NDVI = (double(NIR) - double(R)) ./ (double(NIR) + double(R));
imshow(NDVI, []); % Make sure you use [] because NDVI is floating point.

[Thomas Taufan]

It works!! Thanks for that sir

Can I determine the minimum and maximum value of the NDVI variable? How do I make a threshold for example higher or equal to 0.3 are green and lower than that are red? Can I make bounding box for the specific pixels that has low values?(but in the plant area, not the road or things that are not vegetation)

[Franz Lord Memije]

hi. have you solved this problem already? if you may, kindly share it with me in here. thank you