Additional grayscale algorithms and optimzations #105
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"ClampByte(Round(...))" calls the ClampByte(double) function because Round() returns an Int64 which is too large for ClampByte(integer)). Casting the Round() return value to an Integer fix the "Double=>Int64=>Double=>Byte" conversion.
Added Linear and Colorimetric gray scaling modes. (Linear is the one needed by SVG's filter)
- InvertColors, InvertAlphas: Use of PStaticColor32Array - AdjustHue, AdjustLuminance, AdjustSaturation: Only calculate the new color if the old color is different from the previous color
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This PR adds two additional grayscale algorithms and optimizes some color operations.
Grayscale
The default
TImage32.Grayscalealgorithm changes the saturation of the image, but that is not what SVG gray-scaling does (WebBrowsers, Skia). They use an algorithm that uses the perceptive contrast to generate the gray scale image.This patch doesn't change the default behavior of the
Grayscalemethod, but adds two parameters to it. The first sets the algorithm (Saturation, Linear, Colorimetric) and the second defines the merge amount [0.0-1.0]. The amount parameter doesn't have any effect if "Saturation" is used.I thought about changing the default to "Linear", which is also faster than "Saturation". That would help SVG images. But if someone already uses it for non-SVG things, it would change the behavior.
Performance optimizations
The functions
InvertColorsandInvertAlphasuse PStaticColor32Array instead of incrementing the pointer.The
AdjustHue,AdjustLuminanceandAdjustSaturationfunctions only calculate the new color if the original color is different from the previous color, giving them a huge speed up for larger same color blocks or fully transparent parts in an image.ClampByte(Round(...))
ClampBytehas two overloads. One forIntegerand one forDouble. The (Delphi) compiler always calls the Double-overload if you callClampBytewith the result ofRound. This happens becauseRoundreturns an Int64 and that doesn't fit into an Integer, thusClampByte(Integer)can't be used and the next "best" overload is the Double-overload.So we get "Double->Int64->Double->Int64->Byte" instead of "Double->Integer->Byte".
To prevent this, all the code that uses
ClampByte(Round(...))is replaced withClampByte(Integer(Round(...))).An Int64-overload for
ClampBytewould have been also possible, but the 32bit compiler would become slower, as it would have to push the Int64 onto the stack instead of using a CPU register for theClampByteparameter.Cleanup
The
$IF not declared(NativeInt)isn't necessary. All compilers that are supported (Delphi 7+ and FPC) have that datatype. The only problem with Delphi 7-2007 is that NativeInt can't be used with FOR-loops. So this PR also introduces theSizeIntDatatype for Delphi, that FPC already has. It is an "Integer" for Delphi 7-2007 and a "NativeInt" for all newer Delphi versions, so it can be used with FOR-loops.