Steve on Image Processing

Concepts, algorithms & MATLAB

All about pixel colors: Summary 29

Posted by Steve Eddins,

This week I wrote the last in a series of postings that discussed how MATLAB associates matrix values with specific screen pixel colors. The series talked about the two fundamental image display models (indexed and truecolor); the scaled indexed image variation; using indexed scaling to program brightness/contrast controls; and the grayscale and binary image conventions in the Image Processing Toolbox.

For easy reference, here is the entire series:

  1. Introduction
  2. Truecolor and indexed images
  3. Scaled indexed images
  4. Window-level and CLim
  5. Reference information
  6. Grayscale and binary images

[Updated 10-April-2006 to add link to the reference information post.]


Comments are closed.

29 CommentsOldest to Newest

KOFFI Anderson replied on : 1 of 29

I’m a student and I’d like to learn more in image processing especially images acquisition by CCD Camera

Steve replied on : 2 of 29

Koffi – your question is a little vague, but for camera acquisition I’d point you to the Image Acquisition Toolbox.

Koffi Anderson replied on : 3 of 29

I read your tutorial “laser tracking”;I’d like to know more about the calibration process (algorithm) and the util_findlaser(acquResults).thank you

Prerit replied on : 7 of 29

I am on an project with jpeg 2000 being a part of it.Can you please guide me in making a jpeg 2000 code in matlab- what are the things i need to look for. Or do you have any matlab code for jpeg 2000 where i can actually see what kind of things i need to add more in that in accordance of my work.

gopalakrishnaraja replied on : 11 of 29

I’m a finalyear parttime BE student and also working as development engineer in a color sorting machine manufacturing company.I’d like to learn more in image processing especially images acquisition by CCD Camera

Gopalakrishnaraja – For image processing, you might start with Digital Image Processing by Gonzalez and Woods, or Digital Image Processing Using MATLAB, by Gonzalez, Woods, and Eddins. I don’t know that much about image acquisition, but there is a lot of good information on our web site about the Image Acquisition Toolbox. See this page:

Imtnan replied on : 13 of 29

Dear Steve,

I have written code for EBCOT (JPEG2000) for 2D images as well as 3D images in MATLAB.
But it gives a small diffrence in results when compared to the results of VM 9.0 (Standard JPEG2k) software in bpp values.

Can you please help me finding out my error? I can send you all the code and files if you say so…….

Anxiously waiting for your reply……

Imtnan replied on : 15 of 29

Thanx anyway Bro!

Actually in detail nothing was available to me so i thought to contact you….

Sorry for any waistage of your time

malikireddy replied on : 16 of 29

Hi ,

Iam looking for a method or appliance which can connect my PC/Laptop to the Ultrasound machine , can any one throw some light , which hardware i would need for it , and if again needed some interface software or so , apart from drivers for Hardware and so on …actually i just want to connect the Ultrasound machine and must be able to see the live pictures in Matlab environment .So please advise.

Thanks in advance.


khairiah replied on : 17 of 29

Dear Steve,

It is possible to use Image Acqusition Toolbox to control on shelf digital camera,especially to preview live image and to grab single frame.

hussain replied on : 18 of 29

Hi dear
I am student in Manchester university, pleas I need help in my project to measured the diameter from image ( Used CCD camera to captured image will tool rotating), and find (x,y) coordinate for each line. I write the program in matlab but it not work.

Pleas help.

Thank you

[code deleted—SE]

Steve replied on : 20 of 29

Hussain—I’m sorry, but I can’t help you with debugging your program. Also, a blog comment isn’t the best place for posting a lot of code, so I’m going to delete that part.

khairiah replied on : 21 of 29

how if my camera is not scientific camera and also not firewire type camera but more to commercial type
digital camera.Ex Digital Still camera Sony DSC -F717.
It is I must have certain driver in order to use imaq.

Dave T replied on : 23 of 29


The Image Acquisition Toolbox does not currently support still image cameras, so you will not be able to interface to your camera using Image Acquisition Toolbox.

You will have to write code to interface to your camera. The easiest way to do this would be to find an ActiveX control that can communicate with still image cameras and use MATLAB’s ActiveX interface.

Yicong replied on : 24 of 29


I am working image scrambling in JPEG domain. I am looking the matlab code for JPEG encoding and decoding which can display the compressed result(JPEG image). but I didn’t get it. the matlab code about JPEG compression in your book is only for the algorithm implementation, but how can I display the result of your code?

Please help.

Thanks a lot.

Steve replied on : 25 of 29

Yicong—There are examples showing how to use the code in Chapter 8 of the book. What other information are you looking for?

Abhijit replied on : 26 of 29

Hi Steve,

After capturing the color image on the color CCD camera, I would like to find out at each pixel the wavelength. Can you please help me regarding the procedure I should follow in order to determine the wavelength at each pixel.

Please help. Thanks a lot.


Steve replied on : 27 of 29

Abhijit—I’m not sure that your question makes sense. Except for laser light, the light arriving at any particular sensor has a full spectrum of wavelengths, not just one. That spectrum is filtered according to the characteristic color of the sensor (e.g., red, green, or blue), and a single number recorded. Then the numbers for several neighboring single-color sensors (red, green, and blue) are combined in some way to produce a single RGB pixel.

yasotha.l replied on : 28 of 29

i’m a student and i would like to know about unique color identication in any image and the place of the pixel position.