Unfortunately, the conversion of the JPEG to BMP just cost you a bit of
work and didn't provide you with lossless editing. Here's why:
It's important to realize that JPEG is a *file* format and does not
exist as such inside a photo browser or editor such as FastStone or
PhotoShop. As a file, a JPEG represents a compressed and (variably)
lossy version of the original full resolution, full detail, in-memory
image. When you load a JPEG image the file is reconverted back to its
in-memory, full resolution image.
However, due to the lossy nature of the original JPEG conversion used to
store the file the restored in-memory image has all of the pixels of the
original but lacks some of the detail that was in the original. As a
truly simplistic example, assume a row of blue pixels with blue values
240, 240, 241, 240 240. After the compression and restoration you might
have 240, 240, 240, 240, 240. The outlier 241 value might have been
changed to 240 as unnoticeable and unimportant given the quality level
associated with the particular JPEG. The way JPEG works is a lot more
complicated than my simple example but the example serves to illustrate
the basic point of small quality losses.
When you converted the JPEG to BMP all you did was create a larger file
that had no more information content than the compressed JPEG. The BMP
was essentially an external representation of what would have been
created in-memory anyhow after loading the file into the editor. In
fact, that same in-memory creation from the JPEG had to be performed to
create the BMP in the first place. Sorry, nothing gained. And the next
small quality loss will come when you eventually convert the BMP back
into a JPEG again. Each successive JPEG save results in a small quality
loss. Fortunately, if the JPEG quality level is high it takes many
successive saves to produce a noticeable loss in quality.
All that said, it does make sense to convert to a lossless file format
if you're going to do more than one editing session. Assuming you
started with a JPEG just load the JPEG and edit. If you're sure you're
done editing you can save as a JPEG (but maybe not with the original
name). If you're not finished editing then same the intermediate result
in a lossless format so that the same operation doesn't do another
compression and loss of detail. I would probably choose PNG over BMP.
And if you'd like to avoid loss from the beginning shoot in RAW format
rather than JPEG. But you still have to store intermediate editing
results in a lossless format. And, when editing, stay in 16/48-bit
format if you can... even if you started with an 8 bit JPEG.
Chuck Norcutt
On 1/20/2013 9:48 AM, Brian Swale wrote:
> I had fun with FastStone with this one. I converted the jpeg to a BMP and did
> a quick clone and heal to remove parts of the image I wanted out of it.
> Not perfect as I was too rushed, and also learning how best to do it.
>
> Next times could be better.
>
> When finished converted BMP back to peg. Lossless editing.
>
> Brian Swale
--
_________________________________________________________________
Options: http://lists.thomasclausen.net/mailman/listinfo/olympus
Archives: http://lists.thomasclausen.net/mailman/private/olympus/
Themed Olympus Photo Exhibition: http://www.tope.nl/
|