Thread: How to use loadJPG function from library jpeg?

As I just stated, it is not a standard function. There are many implementations out there for the jpeg format; depending on your compiler/OS/library files the answers are going to be different. You really haven't provided us with any information here. Why don't you post the code you came up with and then maybe provide a link to your instructions; it would be a starting point.

Oh my, let's take a look:

Originally Posted by Homework

1. In this problem we will extend the histogram introduced in previous home-
works to a three dimensional histogram and apply it to compute the his-
togram of a color image.

Do you know what a histogram is?

Originally Posted by Homework

(b) To get the pixels from an actual JPEG image, the image has to
be decompressed first. A library jpeg is provided, which contains
the following function defined in jpeg:h that decompresses a JPEG
image:
// this function reads a JPEG image from file named
// input_file_name
// and stores the pixel data in the file named
// output_file_name
// The function returns the number of bytes written
int loadJPG(const char* input_file_name,
const char * output_file_name);
The output le is a binary le where the rst item is an integer
representing the width of the image, the second item is an integer
representing the height, and then the pixel data follows in the same
way as described in a). Write a function that first calls loadJPG
to decompress the image and then reads into memory the pixel data
written by loadJPG Your function should have the following header:
unsigned char * get_pixels(char * filename,
int *width, int *height);
The function returns a pointer to where the pixel data is stored in
memory and also returns the width and height of the image in pa-
rameters width and height.

If you noticed this is actually part 2 of your problem.

Part 1 would be:

Originally Posted by Homework

Write a function which takes as input a pointer to pixel data, the
width and the height of the image in pixels and the number of bins
for each color and returns a pointer to histogram data. The function
should have this prototype
unsigned int * compute_histogram(
unsigned char * pixels, int width, int height,
int bins_per_color);
The memory where pixels points to is structured such that the rst
item is the blue value of the rst pixel (the upper left corner), the....

So again, what have you done?

Originally Posted by CNoobgrammer

The part I don't understand is how to use the loadJPG function to get all the data I need. Specifically, how to function call loadJPG and read the output of loadJPG into memory.

So did you read the homework assignment at all?

The output file is a binary file where the first item is an integer
representing the width of the image, the second item is an integer
representing the height, and then the pixel data follows in the same
way as described in a).

Originally Posted by CNoobgrammer

Yes, the histogram part is not really a problem.

The part I don't understand is how to use the loadJPG function to get all the data I need. Specifically, how to function call loadJPG and read the output of loadJPG into memory.

Originally Posted by Homework

The output file is a binary fille where the first item is an integer
representing the width of the image, the second item is an integer
representing the height, and then the pixel data follows in the same
way as described in a). Write a function that first calls loadJPG
to decompress the image and then reads into memory the pixel data
written by loadJPG Your function should have the following header:
unsigned char * get_pixels(char * filename,
int *width, int *height);
The function returns a pointer to where the pixel data is stored in
memory and also returns the width and height of the image in pa-
rameters width and height.

How would you do what is in red?

EDIT: To slow again.

May I refer you to the eloquent words of iMalc:

Originally Posted by iMalc

You might think you're appealing to our sympathetic side here, but you're not really. What you are doing is showing that you're an unmotivated person who isn't actively interested in learning programming and leaves things until the last minute. If that's not you then show us a different story.
The kind of person we want to help here is the kind of person who is well motivated to learn programming but for one reason or another just gets stuck on little things here and there, or maybe just needs some clarification or second opinion on their work. Someone who shows they're really trying to learn.

Attempting to dump the problem on others will not get you very far. Think of us more like a physiotherapist who is helping you walk again. It's not our intention to run the race for you. We will only help as much as we can see that you are helping yourself.
Show some real interest in what you are doing. Describe what you're trying to do, and describe what isn't working or what you aren't sure how to do. Just pick one bit that you aren't sure of and start there. Have a go and when you can't figure it out, come and ask about it. Then when we're helped you understand how to solve that bit, work on the next bit.

You're not getting many responses so far because you're not doing these things. I've done you a favour by telling you how you can present yourself as someone who others will actually want to help.