MATLAB: How to create AVI files with a bitdepth of 8-Bit per pixel instead of 24-Bit per pixel in MATLAB 7.7 (R2008b)

MATLAB

I am trying to create an 8-Bit AVI-file from RGB frames. My script converts the RGB frames to 8-bit before putting them in the AVI object. However, the AVI file still appears to be tagged as 24-Bit.

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This behavior is observed possibly because the RGB image data in the MATLAB workspace is of data type DOUBLE or UINT8 and dimension m by n by 3. RGB image data means there are three color channels (Red, Green, Blue) each channel using 8-bits per pixel. As a consequence the resulting AVI-File will have a have bitdepth of 24-bit.

To create an 8-bit AVI-File you will need to convert your image data to either indexed or grayscale (both using 8-bits per pixel). This conversion can be done with RGB2IND or RGB2GRAY. For further details refer to the documentation:

Convert RGB image to indexed image - MATLAB

https://www.mathworks.com/help/matlab/ref/rgb2ind.html

Convert RGB image or colormap to grayscale - MATLAB

https://www.mathworks.com/help/matlab/ref/rgb2gray.html

You may also be interested in the section "More About" of the documentation of the IMAGE command:

Display image object - MATLAB

https://www.mathworks.com/help/matlab/ref/image.html#buryius-5

Related Solutions

MATLAB: Imread bit depth is limited to 8 bit

Most likely you are confusing bits per pixel with bits per color.

The .BMP file header contains the bits per pixel, which is exactly the information that imfinfo returns: in fact the imfinfo help clearly states that the BitDepth gives "Number of bits per pixel." But given that each pixel is divided into three colors, each color plane of that image only uses 8 bits (24 / 3 = 8). This is explained in the imread help.

It is also explained here

https://www.mathworks.com/help/matlab/creating_plots/image-types.html

"Graphics file formats store RGB images as 24-bit images, where the red, green, and blue components are 8 bits each."

When you use imread to import an image it will automatically select the most appropriate numeric class, which for an RGB image are the bits per pixel divided by three, returned as three pages of an array.

As an 8-bit unsigned integer of size MxNx3 is exactly correct for a 24 bit RGB image.

MATLAB: Convert an image with 16 bit depth to 32 or 62 bit in MATLAB

To convert a 16-bit monocromatic image (no colors, black and white) to 32-bit, the below procedure can be followed with gray scale image as reference. Here, Image.png is an RGB image.

Gray = imread('Image.png');
Gray = rgb2gray(Gray);
imwrite(Gray,'imagegrey.png');
grey_info = imfinfo('imagegrey.png');
Grey_BitDepth = grey_info.BitDepth
imwrite(Gray,'imagegrey16.png','BitDepth', 16);
grey16_info = imfinfo('imagegrey16.png');
Grey16_BitDepth = grey16_info.BitDepth

In the above code, maximum valid bit depth for a gray scale image is 16. Also, bit depths 24, 32 and 48 are supported for RGB images in MATLAB. A grayscale image is monochrome. Use this link for reference. https://www.mathworks.com/matlabcentral/answers/78417-can-i-convert-one-image-in-grayscale-to-monochrome

Bit depth of an image:

The image has a bit depth that is shown in the properties of original image under details tab in the file manager i.e. 32 as MATLAB supports only few bit depths that are specific to image file format. An image which has 1456*1936 unit16 value implies that the image has 16 bits/sample. Number of samples for a gray scale image is one and number of samples for rgb image are three.

Use the given link for reference.

https://www.mathworks.com/help/matlab/ref/imread.html

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Related Solutions

MATLAB: Imread bit depth is limited to 8 bit

MATLAB: Convert an image with 16 bit depth to 32 or 62 bit in MATLAB

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