2020-09-17

Dull images

I have been busy on all sorts of little things, none of which seemed worth blogging.

But one of the more fun little distractions was fixing my photo site. I upload images direct from camera on wifi, and they have Exif data extracted and all put in a database. But it was slow, and I ran in to a slight snag with the latest camera. It is still slow, but a complete rewrite of the javascript and the C/database backend has made a hell of a difference.

I am recording images in HEIC (Canon HIF) files. This is 10 bit colour and set with absolute minimal compression. It seems a good compromise. Obviously Canon raw files would be better, and JPG would be easier, but I thought I would give these a try.

There is a nice library called libheif, which has a tool heif-convert which converts the image from the Canon HIF file to JPG. Sorted, or so I thought. I do have to use the latest version as Canon use something odd, it seems, in the header, but that does work.

Unfortunately I am then in a world of weird with colour profiles. The resulting JPG is reduced to 8 bits per colour, as expected, but also has a colour profile applied. This works fine when viewed on my mac and in some browsers. However, it breaks, badly, in other cases. Notably viewing in firefox (even on Mac) and if sent to some social media - twitter just strips the colour profile. Facebook makes an effort. The other issue is various tools to get a thumbnail or make a scaled image, also strip the colour profile. So I had to make things re-apply it at each stage.

The problem is that without the right colour profile the images look, shall we say, dull!

These three images a) with colour profile, b) with profile stripped, c) converted profile.

Update: Blogger fixes the "preview" on image a) here, click on it in firefox to see the problem!


The solution was to use a tool called jpgicc which will convert profiles really quickly on JPG files. Just running it with no options to understand the original profile and convert to a default sRGB for JPG works a treat.

This was not the only issue. The convert from HIF tool also had some slight challenges, but the library allowed me to make my own convertor. The main issue was that the image was coming out of the library rotated correctly - e.g. a portrait image was portrait. This is great until you copy over the Exif data, which says the image needs rotating. The end result is a JPG that claims to need rotating. I was able to strips the rotation from the Exif.

With these two tweaks I now have JPG files that look OK on the photo site, and work for preview on social media, but the raw HEIC available for printing, etc.

I also made nice social media preview links, e.g. https://k.gg/213678

And yes, I know, my photo site is k.gg now, sorry, challenging times.

No comments:

Post a comment

Comments are moderated purely to filter out obvious spam, but it means they may not show immediately.