- From: Tavmjong Bah <tavmjong@free.fr>
- Date: Tue, 07 Dec 2010 11:34:40 +0100
- To: Dr.O.Hoffmann@gmx.de
- Cc: www-svg@w3.org

Hello Olaf, I have been tasked with responding to your email of 13 Jun 2010 concerning the definition of the attribute type for the elements feFunc* defined in: http://www.w3.org/TR/SVG11/filters.html#feComponentTransferTypeAttribute (ISSUE-2338: http://www.w3.org/Graphics/SVG/WG/track/issues/2338 ). My proposed rewording of this section follows. Please let me know if this rewording is satisfactory (your original email is at the bottom). Thanks, Tav ================================================== type = "identity | table | discrete | linear | gamma" Indicates the type of component transfer function. The type of function determines the applicability of the other attributes. In the following, C is the initial component, C' is the remapped component; both in the closed interval [0, 1]. * For identity: C' = C * For table, the function is defined by linear interpolation between values given in the attribute ‘tableValues’. The table has n+1 values (i.e., v_0 to v_n) specifying the start and end values for n evenly sized interpolation regions. Interpolations use the following formula: For a value C < 1 find k such that: k/n <= C < (k+1)/n The result C' is given by: C' = v_k + (C - k/n)*n * (v_k+1 - v_k) If C = 1 then C' = v_n. * For discrete, the function is defined by the step function defined by attribute ‘tableValues’, which provides a list of n values (i.e., v0 to v_n-1) in order to identify a step function consisting of n steps of the same width. The step function is defined by the following formula: For a value C < 1 find k such that: k/n <= C < (k+1)/n The result C' is given by: C' = vk If C = 1 then C' = v_n-1. * For linear, the function is defined by the following linear equation: C' = slope * C + intercept * For gamma, the function is defined by the following exponential function: C' = amplitude * pow(C, exponent) + offset ============================== Original email: Hello www-svg, within the definition of the attribute type for the elements feFunc* http://www.w3.org/TR/SVG11/filters.html#feComponentTransferTypeAttribute there seem to be some variables in the formulas undefined. Is my interpretation correct, that C and C' correspond to the relative channel value the subelement represents? Between 0 and 1? Colors have to be transformed to this range? C before, C' after transformation? For example for feFuncR this means the relative value of the red channel? And what exactly is N? My assumption is, that it is N = n. Is this correct? At least the formulas for table and discrete look useful for C from the interval [0;1) For C = 1 the formulas have the problem, that the v(n+1) for table does not exist and v(n) not for discrete. k is one too large, there is a need to provide another formula for C=1 - something like: use formulas for [0;1) and v(n) for C=1 for table and v(n-1) for C=1 for discrete. For the table type this is only a formal problem, because (C-k/N) = 0 anyway, whatever v(n+1) might be; the result is C' = v(n). Nevertheless the formula should not contain the undefined v(n+1). For the discrete type C'=v(n) for C=1 resulting in k=N is a problem, because the v(i) are defined in such a way, that the last value is v(n-1). Best wishes Olaf

Received on Tuesday, 7 December 2010 10:35:21 UTC