TMC2272A datasheet(10/20 Pages) FAIRCHILD

10 / 20 page

PRODUCT SPECIFICATION

TMC2272A

REV. 1.1.3 10/25/00

Switching Characteristics

Parameter

Conditions

Min

Typ

Max

Units

tDO

Output Delay Time

CLOAD = 25 pF

tHO

Output Hold Time

CLOAD = 25 pF

Applications Discussion

The TMC2272A can convert between any two three-coordinate

colorspaces with the selection of the proper coefficients. Sets

of coefficients for some popular colorspace conversions are

presented below.

By concatenating coefﬁcient matrices of single transforma-

tions, the user can program the TMC2272A to perform

compound transforms efﬁciently. For example, given an

RGB input, correction of the relative values of R and B, for

color temperature, conversion to YIQ, modiﬁcation of

contrast by changing Y, and conversion back to RGB can be

performed as quickly and easily as any simple transformation.

To calculate the ﬁnal set of coefﬁcients from the coefﬁcients

of the individual transformations, the procedure in Figure 7

(concatenation) is used. If more than two matrices are to be

combined, the result from the concatenation of the ﬁrst two

matrices is concatenated with the third. If more matrices

must be incorporated in the ﬁnal function, the last step is

repeated.

Figure 7. Concatenation

PQ R

AJ + BM + CP

DJ + EM + FP

GJ + HM + IP

AK + BN + CQ

DK + EN + FQ

GK + HN + IQ

AL + BO + CR

DL + EO + FR

GL + HO + IR

Converting from GBR to YCBCR

With the right coefficients, two external NOT gates, and an

external 4-bit half-adder, the TMC2272A can convert video

data from 8-bit full-scale (e.g. VGA) GBR components to 10-

bit YCBCR components.

Table 3. 10-bit component formats and

inclusive ranges.

The analog deﬁning equations for 1 Volt luminance and ±0.5

Volt color difference components are:

Y = + 0.5870 (G) + 0.1140 (B) + 0.2990 (R)

B – Y = – 0.3313 (G) + 0.5000 (B) – 0.1687 (R)

R – Y = – 0.4187 (G) – 0.0813 (B) + 0.5000 (R)

To translate these equations into the digital domain, note that

the ranges of R, G, and B are 0 to 255 instead of 0 to 1, the

range of Y is 64 to 940 instead of 0 to 1, and the ranges of U

and V are 64 to 960 instead of +/-0.5:

= (876/255)(0.587(G)+0.114(B)+0.299(R))+64

= 2.01652 (G)+0.39162(B)+1.02715(R) +64

CB = (896/255)(0.3313(G)+0.5(B)-0.1687(R))+512

= -1.16397(G)+1.75686(B)-0.59289(R)+512

CR = (896/255)(-0.4187(G)-0.0813(B)+0.5(R))+512

= -1.47115(G)-0.28571(B)+1.75686(B))+512

Let Y'=Y-64, U'=CB-512, and V'=CR - 512. The TMC2272A

will compute Y', U', and V'. Adding 64 (040h) externally to Y'

will then yield Y, whereas inverting the most signiﬁcant bits of

U' and V', U'9 and V'9, will yield CB and CR, respectively.

Multiplying the equations immediately above by 128 and

rounding each coefﬁcient to the nearest integer yields the rec-

ommended set of coefﬁcients for GBR to YUV conversion.

Color Space Term

Range

Format

Luminance

64-940

magnitude

Y - 64

0-876

magnitude

Color difference,

Blue

64-960

magnitude

CB - 512

±448

2’s comp

Color difference,

Red

64-960

magnitude

CR - 512

±448

2’s comp

GBR

Green, Blue, Red

components

0-255

magnitude,

8-bits

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