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add notes on cast and copy to arithmetic

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This commit is contained in:
John Cupitt 2022-03-23 10:24:24 +00:00
parent 9f351c9c58
commit 62fee01f3a
1 changed files with 15 additions and 1 deletions
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16
libvips/arithmetic/arithmetic.c
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@ -57,7 +57,7 @@
/** /**
* SECTION: arithmetic * SECTION: arithmetic
* @short_description: operations which perform pixel arithmetic, trig, log, statistics * @short_description: pixel arithmetic, trig, log, statistics
* @stability: Stable * @stability: Stable
* @include: vips/vips.h * @include: vips/vips.h
* *
@ -83,6 +83,20 @@
* #VIPS_FORMAT_USHORT image, and taking the vips_cos() of a * #VIPS_FORMAT_USHORT image, and taking the vips_cos() of a
* #VIPS_FORMAT_USHORT image produces #VIPS_FORMAT_FLOAT image. * #VIPS_FORMAT_USHORT image produces #VIPS_FORMAT_FLOAT image.
* *
* After processing, use vips_cast() and friends to take then format back down
* again. vips_cast_uchar(), for example, will cast any image down to 8-bit
* unsigned.
*
* Images have an *interpretation*: a meaning for the pixel values. With
* #VIPS_INTERPRETATION_sRGB, for example, the first three bands will be
* interpreted (for example, by a saver like vips_jpegsave()) as R, G and B,
* with values in 0 - 255, and any fourth band will be interpreted as an
* alpha channel.
*
* After arithmetic, you may wish to change the interpretation (for example to
* save as 16-bit PNG). Use vips_copy() to change the interpretation without
* changing pixels.
*
* For binary arithmetic operations, type promotion occurs in two stages. * For binary arithmetic operations, type promotion occurs in two stages.
* First, the two input images are cast up to the smallest common format, * First, the two input images are cast up to the smallest common format,
* that is, the type with the smallest range that can represent the full * that is, the type with the smallest range that can represent the full