Mirrors/libjpeg-turbo
0
0
Fork 0
mirror of https://github.com/libjpeg-turbo/libjpeg-turbo.git synced 2026-01-18 21:41:20 +01:00
Code Issues Packages Projects Releases Wiki Activity

wizard.txt: Clarify scan script restrictions

Browse Source 
The Wallace paper is not entirely clear on these restrictions, and the
spec itself requires some digging.

Closes #624
This commit is contained in:
DRC
2022-10-21 11:36:29 -05:00
parent 1e9209e3c5
commit e6d1b71029
1 changed files with 9 additions and 1 deletions
Download Patch File Download Diff File Expand all files Collapse all files

10
wizard.txt
View File

@@ -149,7 +149,15 @@ the script represents a progressive or sequential file, by observing whether
Ss and Se values other than 0 and 63 appear. (The -progressive switch is
not needed to specify this; in fact, it is ignored when -scans appears.)
The scan script must meet the JPEG restrictions on progression sequences.
(cjpeg checks that the spec's requirements are obeyed.)
(cjpeg checks that the spec's requirements are obeyed.) More specifically:
* An AC scan cannot include coefficients from more than one component.
* An AC scan for a particular component must be preceded by a DC scan
that includes the same component.
* Only the first AC scan that includes a particular coefficient for a
particular component can include more than one bit from that coefficient.
Scan script files are free format, in that arbitrary whitespace can appear
between numbers and around punctuation. Also, comments can be included: a