Johan van der Knijff’s long-awaited D-Lib paper JPEG 2000 for long term preservation: JP2 as a preservation format, has now come out. In this paper he mentions the various ways LuraWave has handled colour profile information, and I thought it was a good time to elaborate some on the developments we have commissioned from Luratech regarding this issue.
As Johan mentions in the paper, when we started using LuraWave and carrying out JHOVE testing to determine whether the files were compliant with the standard, we found that where an ICC display profile was included in the TIFF (and this was virtual standard across our image set) LuraWave automatically encoded the file as JPX in a JP2 wrapper. This ensured compliance with the standard, but we were not happy with using JPX. So we asked Luratech to modify LuraWave to include an additional command that allowed us to tell the application to ignore the ICC profile completely. This meant that we got a 100% JP2 file, but the colour profile information was then stripped out.
We wanted to include a colour profile in our digital image files. This prevents ambiguity when decoding the images in an image editor or image viewer. We were left with only one option – convert everything to sRGB and allow LuraWave to include the numerical value of sRGB in the file, which is allowed by the standard. Adobe RBG 1998, as Johan explains in detail in his article, is allowed only as an input profile, and our images did not include an input profile (and we didn’t know how we could go about adding an input profile to our images).
We knew that it wouldn’t matter to us, to the user, or to the decoding programme, how the profile was labelled – as long as it was there. It mattered only to the standard. So we asked Luratech to modify LuraWave yet again in order to read the display profile in our TIFFs and embed it into the JP2 file as an input profile. It is not an input profile. But we were limited by the standard, and this was our best option within those limitations to ensure we could include colour information without having to limit ourselves to sRGB – and without having to add in a workflow step to convert all our legacy images to sRGB.
This is the version of LuraWave that we currently use (188.8.131.52 – which includes other enhancements around improving performance, as reported in an earlier blog post). However – since Johan has succeeded in raising awareness of the deficient colour space provision in the standard, leading to agreement in the JPEG Committee to change the standard to accommodate real use scenarios such as our own, we can envisage requesting further changes to the LuraWave command tool once this is finalised.