How to fix poor interpolation of very small rasters in viewed pdfs (evince and chrome)

Question

I want to create a visualization of a matrix for some academic work. I decided to go about this by having the pixels in the image correspond to the values in the matrix. I creat

Answer 1

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An image dictionary in a PDF has an (optional) boolean entry Interpolate. It is specified as a flag indicating whether image interpolation shall be performed by a conforming reader.

The program used by the OP to create the PDF, Inkscape, seems to have explicitly set this flag to true. Editing the PDF to unset this flag creates a file which looks as desired by the OP.

(This also is a solution proposed in this Inkscape forum thread eventually found by the OP, which is to save the PDF with high-resolution bitmaps embedded. File -> Inkscape Preferences -> Bitmaps -> Resolution for Create Bitmap Copy, and set it to 6000 dpi)

The fact that interpolation looks different in different viewers and different output media, is by design. The PDF specification states on interpolation:

A conforming Reader may choose to not implement this feature of PDF, or may use any specific implementation of interpolation that it wishes.

A different way to get around this problem (especially as some PDF viewers have the tendency to not really live up to the specification and e.g. interpolate ignoring that flag) would be to use vector graphics here, drawing the bitmap pixels as rectangles. The result should be optimal.