Hi Jim,
I think the harmless byte that you are referring to will be applied only for
image data(Between SOS(Start of Scan) marker and EOI). For example, any "FF"
data present in Jpeg image will be represented as "FF 00". But I think
application headers or comments section can contain data which will be similar
to EOI,SOI or other markers(FF XX).
Thanks,
Jay
-----Original Message-----
From: Jim Graham
Sent: Friday, June 10, 2016 5:28 AM
To: Jayathirth D V; Philip Race
Cc: 2d-dev@openjdk.java.net
Subject: Re: [OpenJDK 2D-Dev] Review Request for JDK-8152672 : Exception while
getting second image properties for JPEG with embedded thumbnail
It looks like JPEG files have protection for scanning for an FF and assuming it
is a marker by making sure that all FF bytes that appear in data are followed
by a harmless byte, so a brute force search is probably fine. But it still
seems wasteful when we know we are at a tag and we know the sizes of all of the
tags, we should be able to skip around the file looking for the SOI directly...
...jim
On 6/2/2016 5:10 AM, Jayathirth D V wrote:
> Fixed typo.
>
>
>
> *From:*Jayathirth D V
> *Sent:* Thursday, June 02, 2016 5:08 PM
> *To:* Philip Race
> *Cc:* Jim Graham; 2d-dev@openjdk.java.net
> *Subject:* RE: Review Request for JDK-8152672 : Exception while
> getting second image properties for JPEG with embedded thumbnail
>
>
>
> Hi Phil,
>
>
>
> We have two kind of images with which we are able to reproduce the issue:
>
> 1) sample.jpg present in JBS bug(We can't use this image because it
> is licensed ).
>
> 2) JpegEmbedThumbnail.jpg taken using Prasanta's camera and used in
> webrev.
>
>
>
> _ _
>
> _sample.jpg : _
>
> _ _
>
> If we do getNumImages() it will return 2. getNumImages() follows the
> same logic of skipping markers with length and registering SOI to get
> number of images.
>
> sample.jpg has markers as follows :
>
> SOI -> APP1 - > SOI -> EOI -> APP1 End -> EOI -> SOI -> EOI
>
>
>
> I have dumped first image its SOI is first one in the above list and
> for second image it is third one in the list. getNumImages() counts
> first and third SOI for number of images. But in case of skipImage()
> we are getting inside APP1 marker and considering its SOI.
>
>
>
> _JpegEmbedThumbnail.jpg :_
>
> _ _
>
> If we do getNumImages() it will return 1.
>
> JpegEmbedThumbnail.jpg has markers as follows :
>
> SOI -> APP1 -> SOI -> EOI -> APP1 End -> APP2 -> SOI -> APP2 End ->
> APP2
> -> EOI -> APP2 End -> EOI
>
>
>
> getNumImages() counts only first SOI for number of images. But in case
> of skipImage() we will are getting inside APP1 and APP2 markers also.
>
>
>
> Thanks,
>
> Jay
>
> *From:*Phil Race
> *Sent:* Thursday, June 02, 2016 4:05 AM
> *To:* Jayathirth D V
> *Cc:* Jim Graham; 2d-dev@openjdk.java.net
> <mailto:2d-dev@openjdk.java.net>
> *Subject:* Re: Review Request for JDK-8152672 : Exception while
> getting second image properties for JPEG with embedded thumbnail
>
>
>
> I am bit doubtful about this. Are you sure we are correct in reporting
> two images to begin with ?
> Thumbnails should not get counted ..
>
>
> -phil.
>
> On 06/01/2016 01:06 AM, Jayathirth D V wrote:
>
> Updated bug title in JBS as it was misleading.
>
>
>
> *From:* Jayathirth D V
> *Sent:* Wednesday, June 01, 2016 12:48 PM
> *To:* Philip Race; Jim Graham
> *Cc:* 2d-dev@openjdk.java.net <mailto:2d-dev@openjdk.java.net>
> *Subject:* Review Request for JDK-8152672 : Exception getting
> thumbnail size for JPEG with embedded thumbnail
>
>
>
> Hi,
>
>
>
> _Please review the following fix in JDK9:_
>
>
>
> Bug : https://bugs.openjdk.java.net/browse/JDK-8152672
>
>
>
> Webrev : http://cr.openjdk.java.net/~jdv/8152672/webrev.00/
> <http://cr.openjdk.java.net/%7Ejdv/8152672/webrev.00/>
>
>
>
> Issue : When we are trying to get properties related to second image
> in JPEG file we are getting IIOException mentioning that it is not a
> JPEG file.
>
>
>
> Root cause : When we are skipping first image to reach second image
> header, we are just trying to find next available EOI marker. But if
> first image has embedded thumbnail in APP1 marker, we will reach to
> EOI of this thumbnail and not EOI of first image. So after we reach
> EOI of embedded thumbnail we try to access second image SOI marker
> which will fail.
>
>
>
> Solution : We have to change the logic of how we skip to consecutive
> images in JPEG file. We know that application markers, comments or
> other markers can contain data same as SOI & EOI. Instead of just
> checking for EOI marker serially, we should read length of these
> markers and skip them.
>
>
>
> Thanks,
>
> Jay
>
>
>
>
>
