During some past refactor it appears we now end up treating
all JBIG2 images as if they appeared on the last page in the
file. This bug had no visual side ffects but probably led to
suboptimal JBIG2 encoding.
If the color count of an image is low such as when black and white
documents are scanned in color, PNG with lossy quantization may
produce a superior encoding to JPEG. This is expensive to test however.
Previously we opened pngquant-compressed PNGs with transcoding
because the transcode free function in Leptonica didn't seem to
work. This mean Leptonica may have thrown away the hard of
pngquant if didn't understand the encoding.
This change resolves the issue and allows us to open PNG encoded
data and insert it into a PDF without transcoding. Should improve
encoding quality.
* Fix unreachable code
This fixes an issue reported by LGTM.
Signed-off-by: Stefan Weil <sw@weilnetz.de>
* Remove unused imports
This fixes several recommendations from LGTM.
Signed-off-by: Stefan Weil <sw@weilnetz.de>
Soft masks are only allowed to be of colorspace DeviceGray so we
shouldn't use pngquant on them. For now, avoid this exceptional
case by excluded soft masks from optimization.
At some point the color gets flipped, we have to flip it again,
for mono.
Incidentally this exposed an unused
optimization. Should change the
first past to scan all images and
record monochrome xrefs, then optimize
JPEG and PNG, possibly adding
mono images to the monochrome
queue. Finally, do JBIG2 optimization.
James R. Barlow
Stefan Weilandjbarlow83