From 5a422aba704c375a307a902bafe658342e209906 Mon Sep 17 00:00:00 2001 From: scuri Date: Fri, 17 Oct 2008 06:10:15 +0000 Subject: First commit - moving from LuaForge to SourceForge --- html/en/representation.html | 138 ++++++++++++++++++++++++++++++++++++++++++++ 1 file changed, 138 insertions(+) create mode 100644 html/en/representation.html (limited to 'html/en/representation.html') diff --git a/html/en/representation.html b/html/en/representation.html new file mode 100644 index 0000000..1ae5394 --- /dev/null +++ b/html/en/representation.html @@ -0,0 +1,138 @@ + + + + + +Representation + + + + + +

Image Representation Overview

Width and Height

+ +

In the IM library images are 2D matrices of pixels defining width and height. Stacks, Animations, + Videos and Volumes are represented as a sequence of individual images.

+ +

Color Space

+ +

The pixels can have one of several color spaces:

IM_RGB
IM_MAP
IM_GRAY
IM_BINARY
IM_CMYK
IM_YCBCR
IM_LAB
IM_LUV
IM_XYZ .

IM_MAP is a subset of the IM_RGB color space. It can have a maximum of 256 colors. Each + value is an index into a RGB palette.

IM_GRAY usually means luma (nonlinear Luminance), but it can represent any other intensity value that + is not necessarily related to color.

IM_BINARY is a subset of the IM_GRAY color space, and it has only 2 colors black and + white. Each value can be 0 or 1. But for pratical reasons we use one byte to store it.

The other color spaces are standard CIE color spaces, except CMYK that does not have a clear definition without + other parameters to complement it.

+ +

Data Type

+ +

There are several numeric representations for the color component, or several data types:

IM_BYTE
IM_USHORT
IM_INT
IM_FLOAT
IM_CFLOAT.

There is no bit type, binary images use 1 byte (waist space but keep processing simple).

+ +

Color Mode Flags

+ +

To avoid defining another image parameter we also use a parameter called color_mode that it is composed by + the color_space plus some flags, i.e. color_mode = color_space + flags. The flags are binary + combined with the color space, for example color_mode = IM_RGB | IM_XXX. And several flags can be combined in the same + color_mode.

There are 3 flags:

IM_ALPHA
IM_PACKED
IM_TOPDOWN

When a flag is absent the opposite definition is assumed. For simplicity we define some macros that help handling + the color mode:

imColorModeSpace
imColorModeHasAlpha
imColorModeIsPacked
imColorModeIsTopDown

Color Components Packaging (IM_PACKED or unpacked)

+ +

The number of components of the color space defines the depth of the image. The color components can be packed + sequentially in one plane (like rgbrgbrgb...) or separated in several planes (like rrr...ggg...bbb...). Packed color + components are normally used by graphics systems. We allow these two options because many users define their own + image structure that can have a packed or an separated organization. The following picture illustrates the + difference between the two options:

+ +

+ (flag not defined) + IM_PACKED

Separated and Packed RGB Components

Alpha Channel (IM_ALPHA or no alpha)

+ +

An extra component, the alpha channel, may be present. The number of components is then increased by one. + Its organization follows the rules of packed and unpacked components.

+ +

Orientation (IM_TOPDOWN or bottom up)

+ +

Image orientation can be bottom up to top with the origin at the bottom left corner, or top down to bottom with + the origin at the top left corner.

+ +

IM_TOPDOWN + (flag not defined)

Top Down and Bottom Up Orientations

Examples

+ +

IM_RGB | IM_ALPHA - rgb color space with an alpha channel, bottom up orientation and + separated components
+ IM_GRAY | IM_TOPDOWN - gray color space with no alpha channel and top down orientation
+ IM_RGB | IM_ALPHA | IM_PACKED - rgb color space with an alpha channel, bottom + up orientation and packed components

+ + +

Raw Data Buffer

+ +

So these four parameters define our raw image data: width, height, color_mode and data_type. + The raw data buffer is always byte aligned and each component is stored sequentially in the buffer following the + specified packing.

For example, if a RGB image is 4x4 pixels it will have the following organization in memory:

+ +

RRRRRRRRRRRRRRRRGGGGGGGGGGGGGGGGBBBBBBBBBBBBBBBB - for non packed components
+0   1   2   3   0   1   2   3   0   1   2   3

RGBRGBRGBRGBRGBRGBRGBRGBRGBRGBRGBRGBRGBRGBRGBRGB - for packed components
+0           1           2           3

+ +

In bold we visualy marked some lines of data.

+ +

imImage

+ +

We could restrict the data organization by eliminating the extra flags, but several users requested these features + in the library. So we keep them but restricted to raw data buffers.

For the high level image processing functions we created a structure called imImage that eliminates the + extra flags and assume bottom up orientation and separated components. Alpha channel is supported as an + extra component.

The imImage structure is defined using four image parameters: width, height, color_space + and data_type. It is an open structure in C where you can access all the parameters. In addition to the 4 + creation parameters there are many auxiliary parameters like depth, count, line_size, + plane_size and size.

+ + + + + -- cgit v1.2.3