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Remove cHRM check to accomodate ACES AP1 #579

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Remove cHRM check to accomodate ACES AP1 #579

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26 changes: 6 additions & 20 deletions png.c
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Original file line number Diff line number Diff line change
Expand Up @@ -1257,20 +1257,6 @@ png_XYZ_from_xy(png_XYZ *XYZ, const png_xy *xy)
png_fixed_point red_inverse, green_inverse, blue_scale;
png_fixed_point left, right, denominator;

/* Check xy and, implicitly, z. Note that wide gamut color spaces typically
* have end points with 0 tristimulus values (these are impossible end
* points, but they are used to cover the possible colors). We check
* xy->whitey against 5, not 0, to avoid a possible integer overflow.
*/
if (xy->redx < 0 || xy->redx > PNG_FP_1) return 1;
if (xy->redy < 0 || xy->redy > PNG_FP_1-xy->redx) return 1;
if (xy->greenx < 0 || xy->greenx > PNG_FP_1) return 1;
if (xy->greeny < 0 || xy->greeny > PNG_FP_1-xy->greenx) return 1;
if (xy->bluex < 0 || xy->bluex > PNG_FP_1) return 1;
if (xy->bluey < 0 || xy->bluey > PNG_FP_1-xy->bluex) return 1;
if (xy->whitex < 0 || xy->whitex > PNG_FP_1) return 1;
if (xy->whitey < 5 || xy->whitey > PNG_FP_1-xy->whitex) return 1;

/* The reverse calculation is more difficult because the original tristimulus
* value had 9 independent values (red,green,blue)x(X,Y,Z) however only 8
* derived values were recorded in the cHRM chunk;
Expand Down Expand Up @@ -1451,16 +1437,16 @@ png_XYZ_from_xy(png_XYZ *XYZ, const png_xy *xy)
* value of 2 indicates an internal error to the caller.
*/
if (png_muldiv(&left, xy->greenx-xy->bluex, xy->redy - xy->bluey, 7) == 0)
return 2;
return 1;
if (png_muldiv(&right, xy->greeny-xy->bluey, xy->redx - xy->bluex, 7) == 0)
return 2;
return 1;
denominator = left - right;

/* Now find the red numerator. */
if (png_muldiv(&left, xy->greenx-xy->bluex, xy->whitey-xy->bluey, 7) == 0)
return 2;
return 1;
if (png_muldiv(&right, xy->greeny-xy->bluey, xy->whitex-xy->bluex, 7) == 0)
return 2;
return 1;

/* Overflow is possible here and it indicates an extreme set of PNG cHRM
* chunk values. This calculation actually returns the reciprocal of the
Expand All @@ -1473,9 +1459,9 @@ png_XYZ_from_xy(png_XYZ *XYZ, const png_xy *xy)

/* Similarly for green_inverse: */
if (png_muldiv(&left, xy->redy-xy->bluey, xy->whitex-xy->bluex, 7) == 0)
return 2;
return 1;
if (png_muldiv(&right, xy->redx-xy->bluex, xy->whitey-xy->bluey, 7) == 0)
return 2;
return 1;
if (png_muldiv(&green_inverse, xy->whitey, denominator, left-right) == 0 ||
green_inverse <= xy->whitey)
return 1;
Expand Down