From 22f703cab05b7cd368f4de9e03991b7664dc5022 Mon Sep 17 00:00:00 2001 From: =?UTF-8?q?J=C3=B6rg=20Frings-F=C3=BCrst?= Date: Mon, 1 Sep 2014 13:56:46 +0200 Subject: Initial import of argyll version 1.5.1-8 --- tiff/html/man/TIFFcolor.3tiff.html | 975 +++++++++++++++++++++++++++++++++++++ 1 file changed, 975 insertions(+) create mode 100644 tiff/html/man/TIFFcolor.3tiff.html (limited to 'tiff/html/man/TIFFcolor.3tiff.html') diff --git a/tiff/html/man/TIFFcolor.3tiff.html b/tiff/html/man/TIFFcolor.3tiff.html new file mode 100644 index 0000000..7e4eea5 --- /dev/null +++ b/tiff/html/man/TIFFcolor.3tiff.html @@ -0,0 +1,975 @@ + + + + + + +COLOR + + + +

COLOR

+NAME
+SYNOPSIS
+DESCRIPTION
+SEE ALSO
+ +
+ +

NAME

+ + + + + +
+

TIFFYCbCrToRGBInit, TIFFYCbCrtoRGB, TIFFCIELabToRGBInit, +TIFFCIELabToXYZ, TIFFXYZToRGB − color conversion +routines.

+
+ +

SYNOPSIS

+ + + + + +
+

#include <tiffio.h>

+ +

int TIFFYCbCrToRGBInit(TIFFYCbCrToRGB +*ycbcr, float *luma, float +*refBlackWhite");"
+void TIFFYCbCrtoRGB(TIFFYCbCrToRGB *ycbcr, +uint32 Y, int32 Cb, int32 +Cr, uint32 *R, uint32 +*G, uint32 *B );

+ +

int TIFFCIELabToRGBInit(TIFFCIELabToRGB +*cielab, TIFFDisplay *display, +float *refWhite);
+void TIFFCIELabToXYZ(TIFFCIELabToRGB *cielab, +uint32 L, int32 a, int32 +b, float *X, float *Y, +float *Z);
+void TIFFXYZToRGB(TIFFCIELabToRGB *cielab, +float X, float Y, float +Z",uint32*"R, +uint32 *G, uint32 *B);

+
+ +

DESCRIPTION

+ + + + + +
+

TIFF supports several color spaces for images stored in +that format. There is usually a problem of application to +handle the data properly and convert between different +colorspaces for displaying and printing purposes. To +simplify this task libtiff implements several color +conversion routines itself. In particular, these routines +used in TIFFRGBAImage(3TIFF) interface.

+ +

TIFFYCbCrToRGBInit() used to initialize +YCbCr to RGB conversion state. Allocating and +freeing of the ycbcr structure belongs to programmer. +TIFFYCbCrToRGB defined in tiffio.h as

+
+ + + + + +
+
typedef struct {                /* YCbCr->RGB support */
+        TIFFRGBValue* clamptab; /* range clamping table */
+
+
+ + + + + +

int*

+ + + + + + + + + + + + + + + + + + + + + + + +
+ +

Cr_r_tab;
+int*

+		 +
+ +

Cb_b_tab;
+int32*

+		 +
+ +

Cr_g_tab;
+int32*

+		 +
+ +

Cb_g_tab;

+		 +
+ + + + + +
+

int32* Y_tab;
+} TIFFYCbCrToRGB;

+ + + + + +
+

luma is a float array of three values representing +proportions of the red, green and blue in luminance, Y (see +section 21 of the TIFF 6.0 specification, where the YCbCr +images discussed). TIFFTAG_YCBCRCOEFFICIENTS holds +that values in TIFF file. refBlackWhite is a float +array of 6 values which specifies a pair of headroom and +footroom image data values (codes) for each image component +(see section 20 of the TIFF 6.0 specification where the +colorinmetry fields discussed). +TIFFTAG_REFERENCEBLACKWHITE is responsible for +storing these values in TIFF file. Following code snippet +should helps to understand the the technique:

+
+ + + + + +
+
float *luma, *refBlackWhite;
+uint16 hs, vs;
+
+/* Initialize structures */
+ycbcr = (TIFFYCbCrToRGB*)
+
+
+ + + + + + + + + + + + + + + +
+ +

_TIFFmalloc(TIFFroundup(sizeof(TIFFYCbCrToRGB), +sizeof(long))

+
+ +

+ 4*256*sizeof(TIFFRGBValue)

+
+ +

+ 2*256*sizeof(int)

+
+ +

+ 3*256*sizeof(int32));

+
+ + + + + +
+

if (ycbcr == NULL) {
+TIFFError("YCbCr->RGB",

+ + + + + + + +
+ + +

"No space for YCbCr->RGB conversion +state");

+		 +
+ + + + + +
+

exit(0);
+}

+ +

TIFFGetFieldDefaulted(tif, TIFFTAG_YCBCRCOEFFICIENTS, +&luma);
+TIFFGetFieldDefaulted(tif, TIFFTAG_REFERENCEBLACKWHITE, +&refBlackWhite);
+if (TIFFYCbCrToRGBInit(ycbcr, luma, refBlackWhite) < +0)

+ + + + + +
+ +

exit(0);

+
+ + + + + +
+

/* Start conversion */
+uint32 r, g, b;
+uint32 Y;
+int32 Cb, Cr;

+ +

for each pixel in image

+ + + + + +
+ +

TIFFYCbCrtoRGB(img->ycbcr, Y, Cb, Cr, &r, &g, +&b);

+
+ + + + + +
+

/* Free state structure */
+_TIFFfree(ycbcr);

+ + + + + +
+

TIFFCIELabToRGBInit() initializes the CIE +L*a*b* 1976 to RGB conversion state. +TIFFCIELabToRGB defined as

+
+ + + + + +
+
#define CIELABTORGB_TABLE_RANGE 1500
+
+
+
+ + + + + + + + + + + + + + + + + + + + + + + + + + + + + + + + + + + + + + + + + + + + + + + + + + + + + + + + + + + + + + + + + + + + + + + + + + + + + + + + + + + +
+ +

typedef struct {

+		 + + +

/* CIE Lab 1976->RGB support */

+		 +
+ + +

int

+		 + +

range;

+		 + + +

/* Size of conversion table */

+		 +
+ + +

float

+		 + +

rstep, gstep, bstep;

+		 +
+ + +

float

+		 + +

X0, Y0, Z0;

+		 + +

/* Reference white point */

+		 +
+ +

TIFFDisplay display;

+		 +
+ + +

float

+		 + +

Yr2r[CIELABTORGB_TABLE_RANGE + 1]; /* Conversion of Yr +to r */

+		 +
+ + +

float

+		 + +

Yg2g[CIELABTORGB_TABLE_RANGE + 1]; /* Conversion of Yg +to g */

+		 +
+ + +

float

+		 + +

Yb2b[CIELABTORGB_TABLE_RANGE + 1]; /* Conversion of Yb +to b */

+		 +
+ + + + + +
+

} TIFFCIELabToRGB;

+ + + + + +
+

display is a display device description, declared +as

+
+ + + + + +
+
typedef struct {
+
+
+ + + + + + + + + + + + + + + + + + + + + + + + + + + + + + + + + + + + + + + + + + +
+ +

float d_mat[3][3]; /* XYZ -> luminance matrix */

+
+ +

float d_YCR; /* Light o/p for reference white */

+
+ +

float d_YCG;

+
+ +

float d_YCB;

+
+ +

uint32 d_Vrwr; /* Pixel values for ref. white */

+
+ +

uint32 d_Vrwg;

+
+ +

uint32 d_Vrwb;

+
+ +

float d_Y0R; /* Residual light for black pixel */

+
+ +

float d_Y0G;

+
+ +

float d_Y0B;

+
+ +

float d_gammaR; /* Gamma values for the three guns +*/

+
+ +

float d_gammaG;

+
+ +

float d_gammaB;

+
+ + + + + +
+

} TIFFDisplay;

+ + + + + +
+

For example, the one can use sRGB device, which has the +following parameters:

+
+ + + + + +
+
TIFFDisplay display_sRGB = {
+
+
+ + + + + + + + + + + + + + + + + + + + + + + + + + + + + + + + + + + + + + + + + + + + + + + + + + + + + + + + + +
+ +

{ /* XYZ -> luminance matrix */

+		 +
+ + +

{ 3.2410F, -1.5374F, -0.4986F },

+		 +
+ + +

{ -0.9692F, 1.8760F, 0.0416F },

+		 +
+ + +

{ 0.0556F, -0.2040F, 1.0570F }

+		 +
+ +

},

+		 + +
+ +

100.0F, 100.0F, 100.0F, /* Light o/p for reference white +*/

+		 +
+ +

255, 255, 255, /* Pixel values for ref. white */

+		 +
+ +

1.0F, 1.0F, 1.0F, /* Residual light o/p for black pixel +*/

+		 +
+ +

2.4F, 2.4F, 2.4F, /* Gamma values for the three guns +*/

+		 +
+ + + + + +
+

};

+ + + + + +
+

refWhite is a color temperature of the reference +white. The TIFFTAG_WHITEPOINT contains the +chromaticity of the white point of the image from where the +reference white can be calculated using following +formulae:

+
+ + + + + +
+

refWhite_Y = 100.0
+refWhite_X = whitePoint_x / whitePoint_y * refWhite_Y
+refWhite_Z = (1.0 - whitePoint_x - whitePoint_y) / +whitePoint_y * refWhite_X

+ + + + + +
+

The conversion itself performed in two steps: at the +first one we will convert CIE L*a*b* 1976 to CIE +XYZ using TIFFCIELabToXYZ() routine, and at the +second step we will convert CIE XYZ to RGB +using TIFFXYZToRGB(). Look at the code sample +below:

+
+ + + + + +
+
float   *whitePoint;
+float   refWhite[3];
+
+/* Initialize structures */
+img->cielab = (TIFFCIELabToRGB *)
+
+
+ + + + + + +
+ +

_TIFFmalloc(sizeof(TIFFCIELabToRGB));

+
+ + + + + +
+

if (!cielab) {

+ + + + + + + + + + + + + + + + + + + + +
+ +

TIFFError("CIE L*a*b*->RGB",

+		 +
+ + +

"No space for CIE L*a*b*->RGB conversion +state.");

+		 +
+ +

exit(0);

+		 +
+ + + + + +
+

}

+ +

TIFFGetFieldDefaulted(tif, TIFFTAG_WHITEPOINT, +&whitePoint);
+refWhite[1] = 100.0F;
+refWhite[0] = whitePoint[0] / whitePoint[1] * +refWhite[1];
+refWhite[2] = (1.0F - whitePoint[0] - +whitePoint[1])

+ + + + + +
+ +

/ whitePoint[1] * refWhite[1];

+
+ + + + + +
+

if (TIFFCIELabToRGBInit(cielab, &display_sRGB, +refWhite) < 0) {

+ + + + + + + + + + + + + + + + + + + + + + + + + + +
+ +

TIFFError("CIE L*a*b*->RGB",

+		 +
+ + +

"Failed to initialize CIE L*a*b*->RGB conversion +state.");

+		 +
+ +

_TIFFfree(cielab);

+		 +
+ +

exit(0);

+		 +
+ + + + + +
+

}

+ +

/* Now we can start to convert */
+uint32 r, g, b;
+uint32 L;
+int32 a, b;
+float X, Y, Z;

+ +

for each pixel in image

+ + + + + + + + +
+ +

TIFFCIELabToXYZ(cielab, L, a, b, &X, &Y, +&Z);

+
+ +

TIFFXYZToRGB(cielab, X, Y, Z, &r, &g, +&b);

+
+ + + + + +
+

/* Don’t forget to free the state structure */
+_TIFFfree(cielab);

+ +

SEE ALSO

+ + + + + +
+

TIFFRGBAImage(3TIFF) libtiff(3TIFF),

+ +

Libtiff library home page: +http://www.remotesensing.org/libtiff/

+
+
+ + -- cgit v1.2.3