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<!doctype HTML PUBLIC "-//IETF//DTD HTML//EN">
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<meta http-equiv="Content-Language" content="en-us">
<meta http-equiv="Content-Type" content="text/html; charset=iso-8859-1">
<title>Representation Guide</title>
<link rel="stylesheet" type="text/css" href="../style.css">
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<body>
<h1>Image Representation Guide</h1>
<h3 align="left"><a name="raw">Raw Data Buffer</a></h3>
<p align="left">To create a raw image buffer you can simply use the utility function:</p>
<div align="left">
<pre>int width, height, color_mode, data_type;
int size = imImageDataSize(width, height, color_mode, data_type);
void* buffer = malloc(size);</pre>
</div>
<div align="left">
<p align="left">So if the data type is <strong>IM_FLOAT</strong>, we could write:</div>
<div align="left">
<pre>float* idata = (float*)buffer;</pre>
</div>
<div align="left">
<p align="left">Then to locate the pixel at line y, column x, component d simply write:
</div>
<div align="left">
<pre>float value;
if (is_packed)
value = idata[y*width*depth + x*depth + d]
else
value = idata[d*width*height + y*width + x]</pre>
</div>
<div align="left">
<p align="left">But notice that this code will return values at different pixel locations for top down and bottom up
orientations.</div>
<div align="left">
<h3 align="left"><a name="imImage">imImage</a></h3>
</div>
<div align="left">
<p align="left">To use the <b>imImage</b> structure you must include the <im_image.h> header.</div>
<div align="left">
<p align="left">To create an <b>imImage</b> structure you can do it in several ways:</div>
<div align="left">
<pre>int width, height, color_space, data_type, palette_count;
long *palette;
void* buffer
imImage* image;
image = imImageCreate(width, height, color_space, data_type)
image = imImageInit(width, height, color_space, data_type, buffer, palette, palette_count)
image = imImageDuplicate(image)
image = imImageClone(image) </pre>
<p>The <b>imImageInit</b> function allow you to initialize an <b>imImage</b> structure with an user allocated
buffer. This is very useful if you use your own image structure and wants to temporally use the image processing
functions of the library.</p>
<p>To destroy the <b>imImage</b> structure simply call <b>imImageDestroy(image)</b>. If you do "<b>data[0]
= NULL</b>" before calling the destroy function then the raw data buffer will not be destroyed.</p>
</div>
<div align="left">
<p align="left">The <b>imImage</b> data buffer is allocated like the raw data buffer.
</div>
<div align="left">
<p align="left">The separated color components are arranged one after another, but we access the data through an
array of pointers each one starting at the beginning of each color component. So
<b>image->data[0]</b>
contains a pointer to all the data, and <b>image->data[1]</b> is a short cut to the second component and so
on. With this you can use <b>image->data[0]</b> as a starting point for all the data, or use it as the first
component.</div>
<div align="left">
<pre>count = width*height;
unsigned char* idata = (unsigned char*)image->data[0];
for (int i = 0; i < count; i++)
{
idata[i] = 255;
}</pre>
<p>or</p>
<pre>for (int d = 0; d < image->depth; d++)
{
unsigned char* idata = (unsigned char*)image->data[d];
for (int y = 0; y < height; y++)
{
for (int x = 0; x < width; x++)
{
int offset = y * width + x;
idata[offset] = 255;
}
}
}</pre>
</div>
<div align="left">
<p align="left">The <b>imImage</b> structure contains all the image information obtained from a file, because it
also has support for alpha, attributes and the palette. The palette can be used for
<b>IM_MAP</b> images and
for pseudo color of <b>IM_GRAY</b> images.</p>
</div>
<div align="left">
<p align="left">An important subset of images is what we call a <b>Bitmap</b> image. It is an image that can be
directly used into the graphics display. For Bitmap images the color space must be
<b>IM_RGB</b>, <b>IM_MAP</b>,
<b>IM_GRAY</b> or <b>IM_BINARY</b>, and the data type must be <b>IM_BYTE</b>.</div>
<div align="left">
<p align="left">The conversion between image data types, color spaces and the conversion to bitmap are defined only
for the <b>imImage</b> structure.</div>
</body>
</html>
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