The following questions are answered in this section:

    1. How do I find out the coordinates of a pixel?
    2. Is jpegpixi idempotent?
    3. Does jpegpixi increase the file size?
    4. What interpolation methods does jpegpixi support?
    5. Can jpegpixi read progressive JPEG files?


1. How do I find out the coordinates of a pixel?

Any graphics program should be able to help you with this. I personally use
ImageMagick's display program. The middle mouse button shows the coordinates in
a zoomed window.

Alternatively, the jpeghotp program (which is part of the jpegpixi distribution)
finds hot pixel blocks in an otherwise black JPEG image. To obtain an image
suitable for jpeghotp, take a picture with your digital camera in total darkness
or with covered lens.


2. Is jpegpixi idempotent?

Jpegpixi is idempotent (which means that if you run it twice with the same
options, using the output of the first run as the input of the second, the image
is not changed) for images compressed with a very high quality setting. For all
other images, there is an inevitable quality loss in the blocks which contain
the pixels to be interpolated. Of course, other blocks are not affected.


3. Does jpegpixi increase the file size?

Usually the file size is slightly decreased, which is not surprising, since the
data can be better compressed after the interpolation. :-)


4. What interpolation methods does jpegpixi support?

It supports averaging adjacent pixels; linear, quadratic, and cubic
interpolation in one dimension; and bilinear, biquadratic, and bicubic
interpolation in two dimensions.

The command jpegpixi --help shows how to invoke a specific method.


5. Can jpegpixi read progressive JPEG files?

Yes, but it always writes baseline JPEG files.
