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With the help of XnViewMP, I've now examined jpg files produced by some of my cameras which range in age from very new to around 20 years old. So far it looks like none of them know anything about Progressive Mode. In that, maybe the TV makers new what they were talking about when saying they supported jpg files produced by cameras. Might this have been equivalent to saying they did not support Progressive Mode?
My new, Canon Rebel T6, camera was purchased earlier this year. This is a entry level DSLR capable of providing files in the raw format but from what I can see does have quite a bit of processing power.
If camera makers see Progressive Mode as at best unnecessary and for all I know undesirable, why should I want Progressive Mode? I'm inclined to think that I should like what they like. This leads me to a more obvious question which is why would GIMP choose to make Progressive Mode the default? Isn't what I've discovered, we've discussed herein, a good reason that GIMP should caution users and make sure they know the possible consequences of choosing Progressive Mode? Wouldn't it be proper for naive GIMP users, like myself, to expect that their jpg exports are compatible with their cameras?
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"Progressive" mode has been invented for the web. The idea is that if you have a slow connection (think modem... or bad Wifi) you get an idea of the whole image before the whole file is transferred (this is also true for another Web format: PNG). In cameras this doesn't make much sense because the files out of the camera are rarely used on the web , and creating a progressive JPEG possibly requires more RAM and processing power (and don't think that your camera has too much processing power, this is one thing that limits the speed in burst mode)...
On the other hand all cameras do a trick which isn't in the JPEG standard: they encode the orientation of the picture (portrait/landscape) in the EXIF metadata, and the image viewer in WindowsXP was infamous for not handling that properly.
JPEGs produced by Gimp are used on the web in their vast majority so using the progressive mode by default make sense. And if you want something else, it is easy to change the default...
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Another finding! My Thanksgiving holiday has me visiting with family who have more modern electronics than mine. A pretty new TV could display the "Progressive Mode" files without any indication of a difference. I suppose that is good news but until cameras adopt this mode, I'm inclined to want what they support.
With respect to conversion, while bulk/batch mode could be helpful, I think a problem this likely presents is a reduction in quality from success/iterative use of the lossy compression. In that, jpg to jpg conversion is something I've been trying to avoid. At the same time this might be a good opportunity to learn a bit about ImageMagic. I'll do some experimenting.
Also, with respect to my overall objective there is a consideration where www support is relevant. I've been trying to maximize quality which means scanning at fairly high resolution into a lossless file format (i.e., .tif) of directly into GIMP (e.g., a feature I find very desirable). Recognizing that those files which I'm putting onto a web site, run under webtrees, don't need such high resolution, I have been scaling them down to lower resolution. From the lesson received herein it looks like "Progressive Mode" should be used for those files.
