Pixel based Image Data

Collaboration diagram for Pixel based Image Data:

Modules
	Types of Image Data
	The type of the image defines the location and availability of data accessible over the three address pointers, st, ccmp1 and ccmp2. ccmp1 and ccmp2 are the start addresses of the additional color components. The following table gives an overview of the various image types and color components.

Data Structures
struct	image
	Main Structure for Describing Pixel Images. More...

Detailed Description

Images are usually represented by a two-dimensional set of pixels. Since computer memories always have a linear structure, image data is saved in sequence, the pixels are stored in the same order as characters in a (western) book: The image origin is located at position (0,0). This pixel corresponds to the image start address st at the upper left corner. Increasing the x value by one will lead to the next pixel column to the right, increasing the y value by one will lead to the next pixel row downwards. An image consists of dx pixel in the horizontal direction and dy pixel in the vertical direction. Note that the 'last' viewable pixel lies at (dx-1, dy-1).

pitch defines the pixel count going from one pixel to its lower neighbouring pixel (which has the meaning of 'raise the y-value by one'). The advantage of such a parameter – instead of simply adding dx – lies in the ability to define sub-images of a larger image: The pitch of the larger image is also used as pitch for the sub-image, but the dimensions of the sub-image are set to a smaller value, and the start address pointer of the sub-image is set to an address within the larger image. It is clear that pitch must always be equal or greater than dx.

Therefore the address of a pixel should always be calculated using the following formula:

Here, st is the start address of the video memory area (where also the data of the pixel at position (0,0) lies), x and y are the coordinates of the pixel to be addressed by pPx.

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Data Structure Documentation

image

struct image

This structure describes the type of the image, its dimensions and its location in memory. It is the most important structure of the VCLıb.

Data Fields
U8 *	st	Image Data Start Address (Channel 0 Pixel Data).
U32	type	Type of Image Data, Listed in 'Types of Image Data'.
I32	dx	Horizontal Visible Pixel Count.
I32	dy	Vertical Visible Pixel Count.
I32	pitch	Address Offset from a Pixel to its Lower Neighbour Pixel.
U8 *	ccmp1	Color Component 1 (Channel 1 Pixel Data).
U8 *	ccmp2	Color Component 2 (Channel 2 Pixel Data).