what does 4D of an image indicates?

2D means, row and columns of an image.. 3D means.. row,column,RGB... in 4D, what are the dimensions it indicates?

Answer 1

[Image Analyst]

If you have multiple multispectral images then it's a 4D image, for example a stack of color confocal microscopy images where each slice/layer is a 3 color (RGB) image. Or the Visible Human though they may store their data in some special format on disk.

Another example would be a color video where each color frame is a 3D image but you have multiple frames taken at different times. So the 4th dimension is time.

[Sivakumaran Chandrasekaran]

thanks image analyst and thanks walter.. you have multiple frames taken at different times. So the 4th dimension is time. this will match my requirement.

Answer 2

[Jan]

It depends. The 4th component could mean an alpha channel, see "RGBA". Or the image is not stored in RGB colors, but in the CMYK color model. Or you have 4 different layers of grayscale images, e.g. stored in a TIFF file. Or it is any other 4 channel image taken by a camera which records 4 different wavelengths, perhaps green and 3 different infra-read-channels.

[Sivakumaran Chandrasekaran]

Hi Jan, your reply suits my requirement. i used video and image processing blockset.(simulink). the output was stored in workspace in 4D format. I am unable to open that file, because there was more number of pixels in it.

[Walter Roberson]

The 4th dimension is probably for an image sequence. I(:,:,:,J) being for the J'th image.

[Image Analyst]

A multispectral image is a 3D image no matter how many spectral channels it has. If you have multiple multispectral images then it's a 4D image, for example a stack of color confocal microscopy images where each slice/layer is a 3 color (RGB) image.