Form an image of vertical ramp having a ramp values from 0 to 255 and dimension 256x256.

scripy for that???

Answer 1

[John BG]

Pravin

this is ramp

A=uint8(repmat([0:1:255]',1,256))
imshow(A)

.

you can save the image in JPEG format:

.

imwrite(A,'ramp.jpg')

.

if this is the kind of ramp you are looking for would you please be so kind to mark my answer as Accepted Answer?

To any other reader, please if you find this answer of any help solving your question,

please click on the thumbs-up vote link,

thanks in advance

John BG

<mailto:[e-mail] [e-mail]>

[Jan]

@John BG: The square bracket around "[0:1:255]'" are not useful, because there is no reason to apply the concatenation operation. Therefore Matlab's editor shows the corresponding warning here.

The code can be made more efficient by creating the array in the wanted format directly:

1. This creates a double array at first and the converts it to a uint8 afterwards:

uint8(repmat((0:255).', 1, 256))

2. This creates a double vector at first, converts it to an uint8 and produces the matrix efficiently:

repmat(uint8(0:255).', 1, 256))

3. Creating the vector as uint8 directly is the best approach:

repmat((uint8(0):uint8(255)).', 1, 256))

Although the runtime does not matter in the question, it is a nice example for improving the code.

[John BG]

To Mr Jan Simon:

1.

once more, your remark about the bracket is kindly appreciated.

2.

however, you have already mentioned it in other comments and answers, to me and to others, so there is no need for you to repeat your predilection for no brackets.

3.

I prefer using them, it's syntactically correct, and although not needed, it helps new readers grasp the meaning intended.

4.

So, with all due respect, you do it your way, I will do it may way, let others do it their way.

Let the person originating the question decide

John BG

<mailto:[e-mail] [e-mail]>

[Guillaume]

John,

Jan is correct, and it's not a matter of preference. You should not give code to new readers that produces warnings in the editor. You're teaching them to ignore these warnings and then they come here with questions that would be easily solved if they'd actually heeded those warnings.

In this particular case, mlint (hence Mathworks) underlines the square brackets, telling you to replace it with round brackets if necessary.

More importantly, the square brackets are not just syntactical and not a no-op. Remember that square brackets is actually a call to the horzcat function. So your code is actually:

A = uint8(repmat(horzcat(0:255)', 1, 256));

On the same subject the :1: increment is also cruft that really shouldn't be there. 0:255 is more concise, does the same, and doesn't make you wonder if the person misunderstood how colon works (which happens every now and again).

Finally, the last format I'd use to save a gradient is jpeg since jpeg compression is very bad at preserving gradients. png or tiff would be more advisable.

[Jan]

@John BG: Of course you can write your code however you want. And whenever I see the potential to improve code in the forum, I will mention this.

The intented meaning of the [] operator is a horizontal concatenation. As far as I understand, you use it as hint, that the contents is a vector. Beside beeing a personal preference or predilection, this is not efficient and therefore Matlab's editor shows a warning. This should catch the attraction of Matlab beginners. Therefore I explain, how this can be avoided and why this detail matters.

I do not have a list of what I've mentioned before anywhere and when a user finds this thread by google, he will not check my comments in other threads. It is not meant offending in any way, that I repeat this detail. My only intention is to provide all improvements to the code I know. In return I learn a lot from all comments to my code also. So feel free to take such comments as invitation to participate in this community and not as critics.

[John BG]

to Jan Simon and Guillame, you both are wrong on the warning,

MATLAB R2016 does not issue any kind of warning whatsoever, at all, when running the lines supplied.

Of course you may get such warning when running MATLAB earlier versions.

If one tries MATLAB v6.5 it may not run at all.

So, constructive comments are always welcome, but please stop adding disorienting comments that may confuse readers.

Let Mr Pravin Kumar read, comment, and decide whether is the sought answer, or there is need for further development or taking a different direction.

If you want you can start your own answer to this question, not appending, to an earlier answer.

Thanks for your understanding

John BG

[e-mail]

additional note: I repeat, MATLAB 2016 does not produce any kind of warning when running the code supplied. I don't know whether R2009 produces the warning mentioned by Jan Simon, that given his experience I assume it's really the earlier version.

To Jan Simon: for the same price, why aren't you running 2016 or 2017 anyway?

[Image Analyst]

Just to clarify, in R2016b the code does produce an m-lint warning as seen by the orange squiggle underline and the orange line in the right margin.

And as John said, there is no warning in the command window upon running. If the brackets are removed a warning is reported to the command window. If the brackets are replaced by parentheses, there is neither an m-lint warning in the editor, nor a warning in the command window upon running.

[Guillaume]

@John,

As pointed out by Image Analyst, it is a default install of the latest version, R2016b, that gives the warning.

As for 2017-prerelease, as per the NDA you implicitly agreed to if you downloaded it, we're not allowed to talk about it.

[Jan]

For more details about square brackets see Answers: why-not-use-square-brackets

Answer 2

[Jorge Mario Guerra González]

I suppose you want a ramp horizontally, since you only want values from 0-255 in a 256x256 matrix. Filled with integers.

X=uint8(0:255);
x=meshgrid(X,X);
imshow(x, [])

[John BG]

Guerra

your code is not a ramp, all pixels are stuck on the left hand side of the produced image.

[Jan]

@Jorge: The image is displayed correctly either if you use:

X = uint8(0):uint8(255);

or:

X = linspace(0, 1, 256);

[Jorge Mario Guerra González]

Sorry I wrote the code before without using matlab.

X=0:255;
x=meshgrid(X,X);
imshow(x,[])   %although it uses more memory

that one works as well using imshow(x,[ ]), I corrected it