RFR: 8274735: javax.imageio.IIOException: Unsupported Image Type while processing a valid JPEG image [v2]

[Alexander Zuev]

On Fri, 18 Mar 2022 18:21:06 GMT, Phil Race <prr at openjdk.org> wrote:

>> The JDK's built-in Image I/O JPEG plugin decodes JPEGs which are YCbCr and RGb and Grayscale but rejects CMYK and YCCK JPEGs.
>> These would correspond to JFIF encapsulated JPEGs.
>> 
>> This was a reasonable decision to limit support to what was actually likely to be seen - CMYK JPEGs probably should just be created for direct to print devices and never seen on the internet as an interchange format.
>> 
>> Indeed this (below) RFC for mail suggests JFIF is what clients should transmit :
>> 
>> https://datatracker.ietf.org/doc/html/rfc2046 :  Multipurpose Internet Mail Extensions - Part 2
>> 
>> 
>>    A media type of "image" indicates that the body contains an image.
>>    The subtype names the specific image format.  These names are not
>>    case sensitive. An initial subtype is "jpeg" for the JPEG format
>>    using JFIF encoding [JPEG].
>> 
>> And for many years, browsers either failed to display CMYK JPEGs or displayed them incorrectly.
>> 
>> But alas they do crop up and when they do, Image I/O rejects them - to the surprise and
>> consternation of some developer who knows little of JPEGs and arcane colour spaces.
>> 
>> Full support of CMYK JPEGs via the whole Image I/O API including proper handling as metadata
>> will lead us down a path that might even extend into EXIF support for JPEG and likely will
>> require the JPEG Metadata spec to be updated. 
>> 
>> So the goal here is to skirt that as much as possible by just 
>> (1) not rejecting read of CMYK JPEGs and returning a BufferedImage with a suitable ColorModel
>> (2) allowing the same BufferedImage with that ColorSpace to be written back out again as CMYK JPEGs 
>> 
>> Reading will preserve any embedded ICC Color Profile, but writing will not re-encode it since
>> that requires work on metadata. That will have to be a follow-up fix, but at the very least it
>> means that a re-written JPEG will benefit from a default treatment CMYK by any other client.
>> 
>> A test is provided which verifies that the colours are interpreted reasonably, both on initial read
>> and on write and re-read. 
>> 
>> JPEGs with embedded profiles have been tested on read, but since there are licensing issues with those,
>> the test uses JPEGs which have no embedded profile and depend on an internal implementation class.
>> 
>> That class has its hashCode() method updated because testing showed that toString() invoked hashCode()
>> in a way that caused a StackOverflowError - so nothing per se to do with this fix but a necessary update.
>> 
>> Anyone who has trustworthy CMYK JPEGs that render properly in (eg) major web browsers but not with this
>> code can submit those JPEGs so I can evaluate.
>> 
>> But all our automated tests pass as well as some manual testing and evaluation etc.
>
> Phil Race has updated the pull request incrementally with one additional commit since the last revision:
> 
>   8274735: javax.imageio.IIOException: Unsupported Image Type while processing a valid JPEG image

Tested it with some of the CMYK files that i created - seems like all the color conversions are valid and comparing screenshot of the decoded image with the native applications that support the format like Preview or Adobe Photoshop i see no noticeable deviations.

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Marked as reviewed by kizune (Reviewer).

PR: https://git.openjdk.java.net/jdk/pull/7849