Admin: 1 revision

2013-05-09T15:02:00Z

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Gzarkadas at 22:51, 28 February 2008

2008-02-28T22:51:21Z

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{{FilterCat|External_filters|Other_filters|Support_filters}}

{{Func4Def | YV12LUT (clip[, string "yexpr"[, string "uexpr"[, string "vexpr"]]])
| YUY2LUT (clip[, string "yexpr"[, string "uexpr"[, string "vexpr"]]])
| RGBLUT (clip[, string "Rexpr"[, string "Gexpr"[, string "Bexpr"[, string "AMPFile"]]]])
| YV12LUTxy (clipx, clipy[, string "yexpr"[, string "uexpr"[, string "vexpr"]]])
}}

'''Plugin''': [[MaskTools]]

These filters apply a function to each pixel of the picture. In order to allow a fast computation, every possible value of the function are precomputed and stored in a Look-Up Table (hence the name). That makes the filters fairly fast.

{{FuncDef|RGBLUT}} works exactly the same way as {{FuncDef|YV12LUT}}, except that it has an additional argument <tt>AMPFile</tt>. It allows you to load a photoshop color profile.

In order to be able to apply almost every possible function, this one is given by a string which represents an expression in reverse polish notation. The principle of this notation is to write first the operands / parameters of an operator / function, and then the operator / function itself. Hence, "3 + 7" becomes "3 7 +", and "sin(3)" becomes "3 sin". Going further in the explanations, "3 * 7 + 5" becomes "3 7 * 5 +", and "(3 + 7) * 5" : "3 7 + 5 *". Now, you understand the main asset of this notation: no need of parenthesis.

Computations are lead on real numbers. Positive numbers also represent a true statement, whereas negative numbers represent a false statement. In the string, the symbol "x" is tha value of the pixel before the use of the function. For {{FuncDef|YV12LUTxy}} you also have the symbol "y", which represents the value of the collocated pixel in the second clip. The symbols must be separated by a single space.

Some '''operators''' and '''functions''' are implemented :

* +, -, /, *, ^, % are the operators plus, minus, divide, multiply, power and modulo.
* &, |, °, !& are the logical operators and, or, xor, and not. If the result is true, they return 1.0, else -1.0.
* <, <=, >, >=, =, != are the relationnal operators less than, less or equal to, more than, more or equal to, equal to, not equal to. If the result is true, they return 1.0, else -1.0.
* cos, sin, tan, acos, asin, atan, exp, log, abs are the functions cosine, sine, tangent, arccosine, arcsine, arctangent, exponential, napierian logarithm, absolute value.
* ? allows to do a condition test. It's a ternary operator, the first operand being the condition, the second the value if the condition is true, the third if false.

Some '''examples''':

* Binarization of the picture with a threshold at 128:
"x 128 < 0 255 ?"
: It is translated as:
"(x < 128) ? 0 : 255"

* Levels(il, gamma, ih, ol, oh) (have a look at the filter [[Levels]]):
"x il - ih il - / 1 gamma / ^ oh ol - *"
: It is translated as:
"(((x - il) / (ih - il)) ^ (1 / gamma)) * (oh - ol)"

Defaults are: <tt>Yexpr</tt> = <tt>Uexpr</tt> = <tt>Vexpr</tt> = "x" (hence, the filter does nothing ).

----
Back to [[MaskTools]].

MaskTools/YV12LUT - Revision history

Admin: 1 revision

Gzarkadas at 22:51, 28 February 2008