how can i solve this problem ?

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[Ameer Hamza]

Can you paste complete error message? From the given image it appear that you should move the line

Y = imread('xyz.jpg');

at the start of the script.

[Rik]

You should really paste your code as text (use the {}Code button for formatting), and include the entire error message. It gives information about the nature of the error. Does the variable Y exist? Does it contain an array that is a valid input so it can be written to jpeg? Is the q variable valid (i.e. is it indeed a scalar in the range 0-100)?

It would be easy to see which of these occurred if you look at the complete message.