On Sat, Oct 23, 2010 at 2:11 PM, Mark Phillips wrote:

My apologies for this OT post, but I need some help from an "image expert", and I thought the Gimp list might have one or two. When I upload images from a friend's digital camera, a Java web app is not able to create thumbnails (they appear black with the title of the image in the image area). However, clicking on the missing thumbnail renders the full image. When I upload images from a different camera, the same app generates the thumbnail and also renders the full image. Is there a special setting that camera's have to have set to allow thumbnails to be created? Both file types are jpeg. I am not seeing any error messages from the app.

Yep, definitely off-topic :p

Those applications you mentioned probably aren't generating thumbnails. They're just using the existing thumbnail that's embedded in the file. Most cameras embed a thumbnail in the JPG file, some do not. Your friend's camera probably just doesn't have those thumbnails embedded.

To keep this on-topic: Gimp and most other image editors have an option to include a thumbnail when saving a JPG file. I typically disable this option for web graphics to make the file size smaller.

-- Frank Gore
THE place to talk photography!
www.friendlyphotozone.com

On 10/23/2010 02:27 PM, Frank Gore wrote:

On Sat, Oct 23, 2010 at 2:11 PM, Mark Phillips wrote:

My apologies for this OT post, but I need some help from an "image expert", and I thought the Gimp list might have one or two. When I upload images from a friend's digital camera, a Java web app is not able to create thumbnails (they appear black with the title of the image in the image area). However, clicking on the missing thumbnail renders the full image. When I upload images from a different camera, the same app generates the thumbnail and also renders the full image. Is there a special setting that camera's have to have set to allow thumbnails to be created? Both file types are jpeg. I am not seeing any error messages from the app.

Yep, definitely off-topic :p

Those applications you mentioned probably aren't generating thumbnails. They're just using the existing thumbnail that's embedded in the file. Most cameras embed a thumbnail in the JPG file, some do not. Your friend's camera probably just doesn't have those thumbnails embedded.

To keep this on-topic: Gimp and most other image editors have an option to include a thumbnail when saving a JPG file. I typically disable this option for web graphics to make the file size smaller.

-- Frank Gore

One caution that should be mentioned if the OP decides to use the Gimp option Frank mentioned to generate thumbnails when saving JPG files. If the JPG is opened in gimp and then saved (even though "no changes" are made), the JPG will suffer some amount of quality loss even if the highest quality level is selected when saving. I run into a _lot_ of people who are simply not aware that _every_ time a JPG is saved, the quality is reduced.

BTW, to accomplish the addition of the preview in Gimp in this circumstance you need to use "Save As" (probably on top of the same name) and tick the checkbox about preview images. Make sure the quality slider is all the way to maximum.

Test this all first by copying one or more images to a different directory/folder and working on the copy.

Jay

On 10/23/2010 08:50 PM, Jay Smith wrote:

One caution that should be mentioned if the OP decides to use the Gimp option
Frank mentioned to generate thumbnails when saving JPG files. If the JPG is
opened in gimp and then saved (even though "no changes" are made), the JPG will
suffer some amount of quality loss even if the highest quality level is selected
when saving. I run into a _lot_ of people who are simply not aware that _every_
time a JPG is saved, the quality is reduced.

This is definitely not true... Try this:

- load an image in Gimp - save it as JPEG, using whatever settings you fancy (note; even if the file is alreay a JPEG, it's important to save it here...). Let's call it "original.jpg".
- close image
- reload "original.jpg"
- do a local edit on it (for instance, small circle selection plus bucket fill)
- save it with same settings (Gimp will normally reuse the ones used in the loaded image) as "edited.jpg"
- close image
- reload original.jpg
- load edited.jpg as a new layer
- put the "edited" layer in difference mode. You'll only see the bit of the image you replaced by a circle, the rest is black. - to see how black is the black, flatten the image and open the histogram dialog.
- select any part of the image outside the edited circle. Under the histogram, if you use a minimum value above 0, the count is 0, in other words, the difference between the original and edited picture is 0 everywhere, and there is no loss.

I have Perl a script that runs Imagemagick multiple times against the same image (a white dot is added each round)(*). Then it uses imagemacick's compare to general the diff image. after two or three iterations the only thing in the diff image is the white dot added even with very low JPEG quality settings (the difference on the first iterations is due to imagemagick not using the same settings as the original image, in particular a different color subsampling)(this is why it was important to save the image from Gimp the first time above).

This is because the Jpeg algorithm is stable, and the decoded pixels get re-encoded in the very same values if encoding settings aren't changed.

Things are obviously different after a global change to the picture (contrast, white balance, etc...)

(*) I won't post it here but interested people can drop me a mail. It was written for Windows but will likely run under Linux with minor changes.

-- Ofnuts

On Sat, Oct 23, 2010 at 4:32 PM, Ofnuts wrote:

This is definitely not true... Try this:

How ironic that an off-topic original question would go so wildly off-topic...

-- Frank Gore
THE place to talk photography!
www.friendlyphotozone.com