# Semantics
* Chunk data is stored in `spng_ctx`.
* When calling `spng_get_*()` or `spng_set_*()` functions all
chunks up to the first IDAT are read, validated then stored,
with the exception of `spng_get_ihdr()`, which only reads the
the header.
* When calling `spng_get_*()` after the image has been decoded all
chunks up to the IEND marker are read.
* `spng_set_*()` functions replace stored chunk data for that type.
* Chunk data stored with `spng_set_*()` functions are never replaced with
input file chunk data i.e. if you set something it will stay that way.
* All `spng_get_*()` functions return 0 on success and non-zero error or
`SPNG_ECHUNKAVAIL` if the PNG does not contain that chunk.
# API
# spng_get_ihdr()
```c
int spng_get_ihdr(spng_ctx *ctx, struct spng_ihdr *ihdr)
```
Get image header
# spng_get_plte()
```c
int spng_get_plte(spng_ctx *ctx, struct spng_plte *plte)
```
Get image palette
# spng_get_trns()
```c
int spng_get_trns(spng_ctx *ctx, struct spng_trns *trns)
```
Get image transparency
# spng_get_chrm()
```c
int spng_get_chrm(spng_ctx *ctx, struct spng_chrm *chrm)
```
Get primary chromacities and white point as floating point numbers
# spng_get_chrm_int()
```c
int spng_get_chrm_int(spng_ctx *ctx, struct spng_chrm_int *chrm_int)
```
Get primary chromacities and white point in PNG's internal representation
# spng_get_gama()
```c
int spng_get_gama(spng_ctx *ctx, double *gamma)
```
Get image gamma
# spng_get_iccp()
```c
int spng_get_iccp(spng_ctx *ctx, struct spng_iccp *iccp)
```
Get ICC profile
!!! note
ICC profiles are not validated.
# spng_get_sbit()
```c
int spng_get_sbit(spng_ctx *ctx, struct spng_sbit *sbit)
```
Get significant bits
# spng_get_srgb()
```c
int spng_get_srgb(spng_ctx *ctx, uint8_t *rendering_intent)
```
Get rendering intent
# spng_get_text()
```c
int spng_get_text(spng_ctx *ctx, struct spng_text *text, uint32_t *n_text)
```
Copies text information to `text`.
`n_text` should be greater than or equal to the number of stored text chunks.
If `text` is NULL and `n_text` is non-NULL then `n_text` is set to the number
of stored text chunks.
Strings may be zero-length (single `'\0'` character) with the exception of `text.keyword`,
all strings are guaranteed to be non-NULL.
!!! note
Due to the structure of PNG files it is recommended to call this function
after `spng_decode_image()` to retrieve all text chunks.
!!! warning
Text data is freed when calling `spng_ctx_free()`.
# spng_get_bkgd()
```c
int spng_get_bkgd(spng_ctx *ctx, struct spng_bkgd *bkgd)
```
Get image background color
# spng_get_hist()
```c
int spng_get_hist(spng_ctx *ctx, struct spng_hist *hist)
```
Get image histogram
# spng_get_phys()
```c
int spng_get_phys(spng_ctx *ctx, struct spng_phys *phys)
```
Get phyiscal pixel dimensions
# spng_get_splt()
```c
int spng_get_splt(spng_ctx *ctx, struct spng_splt *splt, uint32_t *n_splt)
```
Copies suggested palettes to `splt`.
`n_splt` should be greater than or equal to the number of stored sPLT chunks.
If `splt` is NULL and `n_splt` is non-NULL then `n_splt` is set to the number
of stored sPLT chunks.
!!! warning
Suggested palettes are freed when calling `spng_ctx_free()`.
# spng_get_time()
```c
int spng_get_time(spng_ctx *ctx, struct spng_time *time)
```
Get modification time
!!! note
Due to the structure of PNG files it is recommended to call this function
after `spng_decode_image()`.
# spng_get_offs()
```c
int spng_get_offs(spng_ctx *ctx, struct spng_offs *offs)
```
Get image offset
# spng_get_exif()
```c
int spng_get_exif(spng_ctx *ctx, struct spng_exif *exif)
```
Get EXIF data
!!! note
Due to the structure of PNG files it is recommended to call this function
after `spng_decode_image()`.
!!! warning
`exif.data` is freed when calling `spng_ctx_free()`.
# spng_set_ihdr()
```c
int spng_set_ihdr(spng_ctx *ctx, struct spng_ihdr *ihdr)
```
Set image header
# spng_set_plte()
```c
int spng_set_plte(spng_ctx *ctx, struct spng_plte *plte)
```
Set image palette
# spng_set_trns()
```c
int spng_set_trns(spng_ctx *ctx, struct spng_trns *trns)
```
Set transparency
# spng_set_chrm()
```c
int spng_set_chrm(spng_ctx *ctx, struct spng_chrm *chrm)
```
Set primary chromacities and white point as floating point numbers
# spng_set_chrm_int()
```c
int spng_set_chrm_int(spng_ctx *ctx, struct spng_chrm_int *chrm_int)
```
Set primary chromacities and white point in PNG's internal representation
# spng_set_gama()
```c
int spng_set_gama(spng_ctx *ctx, double gamma)
```
Set image gamma
# spng_set_iccp()
```c
int spng_set_iccp(spng_ctx *ctx, struct spng_iccp *iccp)
```
Set ICC profile
`spng_iccp.profile_name` must only contain printable Latin-1 characters and spaces.
Leading, trailing, and consecutive spaces are not permitted.
!!! note
ICC profiles are not validated.
# spng_set_sbit()
```c
int spng_set_sbit(spng_ctx *ctx, struct spng_sbit *sbit)
```
Set significant bits
# spng_set_srgb()
```c
int spng_set_srgb(spng_ctx *ctx, uint8_t rendering_intent)
```
Set rendering intent
# spng_set_text()
```c
int spng_set_text(spng_ctx *ctx, struct spng_text *text, uint32_t n_text)
```
Set text data
`text` should point to an `spng_text` array of `n_text` elements.
`spng_text.text` must only contain Latin-1 characters.
Newlines must be a single linefeed character (decimal 10).
`spng_text.translated_keyword` must not contain linebreaks.
`spng_text.compression_method` must be zero.
# spng_set_bkgd()
```c
int spng_set_bkgd(spng_ctx *ctx, struct spng_bkgd *bkgd)
```
Set image background color
# spng_set_hist()
```c
int spng_set_hist(spng_ctx *ctx, struct spng_hist *hist)
```
Set image histogram
# spng_set_phys()
```c
int spng_set_phys(spng_ctx *ctx, struct spng_phys *phys)
```
Set phyiscal pixel dimensions
# spng_set_splt()
```c
int spng_set_splt(spng_ctx *ctx, struct spng_splt *splt, uint32_t n_splt)
```
Set suggested palette(s).
`splt` should point to an `spng_splt` array of `n_splt` elements.
# spng_set_time()
```c
int spng_set_time(spng_ctx *ctx, struct spng_time *time)
```
Set modification time
# spng_set_offs()
```c
int spng_set_offs(spng_ctx *ctx, struct spng_offs *offs)
```
Set image offset
# spng_set_exif()
```c
int spng_set_exif(spng_ctx *ctx, struct spng_exif *exif)
```
Set EXIF data