Re: [matplotlib-devel] image module questions

[John H. <jdh...@ac...>]

>>>>> "Perry" == Perry Greenfield <pe...@st...> writes:
  
    Perry> Todd and I just talked about this. There are two possible
    Perry> approaches, one of which should work and the other which we
    Perry> would have to think about. The simpler approach is to write
    Perry> a C extension using the Numeric API. As long as a small,
    Perry> rarely-used, subset of the Numeric API is not used (the
    Perry> UFunc API and some type conversion stuff in the type
    Perry> descriptor) 

OK, I'll start with plain vanilla Numeric along the lines Todd sent me
earlier, and we can do the (apparently straightforward)
numarray/numeric port when we have a prototype.

    Perry> I agree that this is the drawback. On the other hand,
    Perry> processor memory has grown much faster than image display
    Perry> memory. With a full screen image of 1024x1280 pixels, we
    Perry> are only talking about 5MB or so for a 32-bit deep
    Perry> display. Converting rgba all to floats means 20MB, while
    Perry> large is not overwhelming these days, and that is the worst
    Perry> case for interactive cases. I suppose it would be a bigger
    Perry> concern for non-interactive situations (e.g. PDF). But it
    Perry> would seem that in doing this simpler approach, we would
    Perry> have something that works sooner, and then we could think
    Perry> about how to handle cases where someone wants to generate a
    Perry> 4Kx4K PDF image (which is going to be one big PDF
    Perry> file!). I'd let's not let extreme cases like this drive the
    Perry> first implementation.

Agreed.  If noone has any objections I think I'll start with rgba32 as
the common rendering format for the image module and we can special
case the smaller (grayscale UInt8 or UInt16) and larger (rgba floats)
cases after a prototype implementation.

I'm imagining an interface like

Frontend:

 im = image.fromarray(A)                 # NxM  
 im = image.fromarray(A, colormap)       # NxM colormapped images
 im = image.fromarray(A)                 # NxMx3, no format needed
 im = image.fromarray(A)                 # NxMx4, no format needed
 im = image.fromfile('somefile.png')

 im.set_interpolate(image.BILINEAR)
 im.set_aspect_ratio(image.CONSTRAINED)

Backend:
  
  def draw_image(im):
      # Ascaled is width x height x 4 resampled using interpolation
      # and aspect constraints from above
      Ascaled = im.resize(viewport.width, viewport.height)
      renderer.draw_from_rgba(Ascaled, etc1, etc2)

    Perry> Well, I was just referring to the image file support that
    Perry> PIL supplies; the rest of PIL seems mostly redundant with
    Perry> matplotlib and array capabilities (if I remember right, I
    Perry> haven't really used PIL much).  How much image file format
    Perry> support is built into agg?

Almost none, except for the raw (or almost raw) image types (ppm,
bmp).  PNG, I have more or less figured out; borrowing the read/write
capabilities for other image format from PIL is a good idea.

JDH