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

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Pravin Kumar 2017-1-24

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评论： Jan 2017-1-26

采纳的回答： John BG

scripy for that???

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Answer 1

John BG 2017-1-25

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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:jgb2012@sky.com jgb2012@sky.com>

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Guillaume 2017-1-25

编辑：Guillaume 2017-1-25

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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 2017-1-25

@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 2017-1-26

编辑：John BG 2017-1-26

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

jgb2012@sky.com

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?

Guillaume 2017-1-26

@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 2017-1-26

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

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Answer 2

Jorge Mario Guerra González 2017-1-24

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编辑：Jan 2017-1-26

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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, [])

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Jan 2017-1-25

编辑：Jan 2017-1-25

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@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 2017-1-25

编辑：Jorge Mario Guerra González 2017-1-25

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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

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

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

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