Re: Incorrect density values when quantifying PNG files exported from GIMP

Posted by Robert Baer on Nov 20, 2012; 10:27pm
URL: http://imagej.273.s1.nabble.com/Incorrect-density-values-when-quantifying-PNG-files-exported-from-GIMP-tp5000862p5000908.html

On 11/20/2012 3:47 PM, Robert Baer wrote:

> On 11/20/2012 2:38 PM, Garvalov, Boyan wrote:
>> - This issue indeed appears to be at the heart of the problem, but I
>> actually cannot give you a straight answer right now. I can only tell
>> you the following:
> -- snip --
>> 4) The problem only occurs when I copy (a part of) one image and
>> paste it into a new file in GIMP which I then export as png from
>> GIMP. In that case it doesn’t help if I tell GIMP to open the new
>> file as grayscale and it makes no difference if I define the fill
>> color as white, foreground (black) or transparent.
> If you look at the layers tab in GIMP, you will see that a new GIMP
> image by default has a [blank] background layer (like photoshop). When
> you paste your copied image to the image there are now two layers that
> get saved. Both .tif and .png formats support saving multilayered
> images. .jpg does not. When you flatten the image as Wayne suggested,
> you are collapsing all the layers of the image into a single layer
> with layers higher in the layer stack "writing over" layers lower in
> the stack. ImageJ treats "layers" as stack frames which have different
> and more complex meanings in different contexts (time, color channel,
> z-depth, etc.). My guess is that everything that happens when using
> GIMP would have similar behavior in Photoshop although I think newer
> versions of Photoshop have better support for 16-bit images. The GIMP
> behavior is not necessarily a bug, but rather a different perspective
> on how to treat multiframe images. This probably also explains the
> first sentence of #5 below.

Hmmm ...
Looks like GIMP 2.8 DOES NOT support saving layers.  In fact it does not
seem to support layer saving  except for its native .xcf format as
nearly as I can now tell.  I take back what I implied about this being
simple to understand...   And yes, maybe it IS a GIMP bug ... Fireworks
supports multilayer .png files, but I guess this is not a part of the
basic specification.

I've learned alot from your problem Boyan -- but the most important
thing is how many misconceptions I have!

Rob

--
ImageJ mailing list: http://imagej.nih.gov/ij/list.html