为什么SVG图片的CSS大小难以调整（已通过Chrome，Firefox的测试）

Question

I can reproduce this issue in both Chrome and Firefox.

This is SVG image in question: https://www.iconfinder.com/icons/284101/editor_hambuger_list_menu_view_icon#size=512

And this is the minimum code which reproduces the problem:

<img 
style="width: 15px; vertical-align: middle;"
src="data:image/svg+xml;base64,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" /> Menu

You can play with it and see it in action at: http://jsfiddle.net/adamovic/s3dZ2/1/

Anyone has an idea why this Scalable Vector Graphics gets resize where lines becomes unproportional and also any idea how to fix this good?

BTW, in production I'm resizing this image to 1EM, to appear next to text "Menu" but to reproduce this issue it is the simplest way.

UPDATE: Updated example from 11.5px to 15px, reproducing same issue.

In production I'm using width: 1EM; or something like that for responsive design, any idea how to responsive scale this image so that lines are proportional?

Maybe some fix like min-width and max-width could work, but I couldn't make it work ever with some mozilla image specific commands.

Answer 1

At 11.5 pixels in with the height of the image should be 6.3 pixels. Of those, 1.1 pixels should be the height of each black line, and 1.5 pixels the height of each white line. And on top of that the browser resizes the picture to 6 pixels height.

If the image had 1 pixels for each line (both white and black) and the size multiple of 5, it would look great.

Later edit In the given picture a black line is 16.67% of image size(all lines reprezent 50%) and a white line is 25%. So... for a height of 8 pixels the a black line has a height of 1.3 pixels and aa white line 2 pixels. On paper the smallest image that looks good and unaltered has 2 pixels for black line and 3 for the white line, meaning an image with 12 pixels height.

Basically if one pixel has to share both white and black lines the browser will create a shade of gray that is the average of the two as it can only display one color .

EX : a pixel has to show 0.67 white(#FFFFFF or 255,255,255) and 0.33(#000000 or 0,0,0) black: 0.67*255 + 0.33*0 = 170.85 (aproximatly 171) so the color displayed is (#ABABAB or 171,171,171)

Answer 2

Theoretically, SVG image is infinitely scalable. In practice however, the screen has limited resolutions, so if you scale an SVG too small, it won't look very good due to pixelations.

To avoid this problem, you need to set a minimum size for the icon at the point where it still looks good. High quality small-sized vector iconsets would usually be designed to have in such a way that their major lines lie in a grid of integer proportion for many different sizes, so that they will look crisp on different sizes; some icon designers might also provide a separately-drawn raster icons for low resolutions.

Inferring from the size declaration in the SVG, the icon you linked seems to have been designed for 22x12 or multiples of it.

On small sizes, you probably should also use media-queries so that small icons are scaled in a step-ladder of sizes with sizes that are known to look good rather than strictly depending on the viewport size.