rasterize() to output 408.24 µm field as 1080BMP, 0.378 µm line became 2 pixels instead of 1 pixel

Flyingmyd

I used the rasterize() function to convert GDS to BMP. My goal is to split the GDS image into fields of 408.24 [um], with the output image being 1080x1080, and achieving a resolution of 0.378 microns per pixel.
However... almost all areas (except for two specific points I marked) became two pixels wide instead of the one-pixel width I set. I’m currently working on finding the cause of this issue.
Heres is my python ,GDS and Bmp Output.

dick_freebird

Still think this is rounding error residue / "DBU beat frequency" stacking up.

Does your source data have such a funky DBU initially?

If so then maybe you must first upscale DBU per distance to a least-common-multiple, rasterize that, and then downscale (basic image resize) to the target pixel scale and count.

Now all I know about changing DBU on the fly is, "better left alone if you don't know what you're doing" so I don't. But I think this is what you need for harmonizing source and product per goal.

Matthias

Hi @Flyingmyd,

@dick_freebird is right - the layout is not aligned with the grid you're using.

Let me demonstrate what happens by using grayscale values:

        rgb = int(math.floor(a * 255.0 / (pixel_size_dbu.x * pixel_size_dbu.y) + 0.5)) * 0x10101

For example this line:

Comes out as a two-pixel grayscale line:

The reason is that with this rasterization:

2025-01-11 18:33:44,840 - DEBUG - box_to_render_dbu: (0,0;408240,408240)
2025-01-11 18:33:44,840 - DEBUG - pixel_size_dbu: 378,378

and these coordinates of the line rectangle:

![](https://www.klayout.de/forum/uploads/editor/4r/g7jih72v5v03.png "")

the line is on the 0.378 µm grid vertically as 102.06 and 204.12 are integer multiples of 0.378, but not horizontally: 103.742 and 104.12 are not integer multiples of 0.378. In other words, the line sits between two pixels and overlaps both of them. Hence, the area covered by the line is divided between the left and right pixel column.

In your code you set the color to white when the area is not null - this means the non-zero area contributions of the line make it 2 pixels wide.

The layout has to fit precisely on the rasterization grid to render exactly 0 or non-zero area values.

Matthias