How do I put an image into Illustartor document at its actual size?

I’m creating a new document, choosing Web profile, setting width and height equal to image size. But the image appears half as big as it really is. That is, I need to place image 4 times to fill the document. Why is that? Am I missing something?

UPD Sorry for not saying it explicitly, I’m specifying document extents in pixels, and choosing resolution 72 ppi.

UPD As for my question being marked as duplicate. The suggested question indeed clarifies that Raster Effects is not Document’s Resolution, and is ignored when pasting images. When using Web profile, images are being pasted as if the document has 72 ppi. Since pixels in Illustrator was redefined as physical units, such that 1 inch = 72 pixels.

But it doesn’t address my other source of confusion. And the fact to be considered when pasting images. Images, specifically png ones, can contain information about physical extents.

Answer

First, there is no such thing as Illustrator document’s ppi. It just treats pixels as physical units, such that 1 inch = 72 pixel.

Second, Raster Effects has no effect on how big Illustrator makes an image pasting it in a document.

So, if you create a document with dimensions 1920×1080 pixels, and paste an 144 ppi image of the same dimensions, it ends up taking quarter of the document. Since 1920 pixels of the image are supposed to take 1920 / 144 inches, which is 1920 / 144 * 72 = 960 = 1920 / 2 pixels.

In other words, one might say, Illustrator pastes an image as if the document has 72 ppi when document extents are given in pixels.

Third, when doing screenshots on Windows with Snipping Tool, resulting image’s ppi depends on size of “text and other items”. Where Smaller - 100% corresponds to 96 ppi, Medium - 125% to 120 ppi, and Larger - 150% to 144 ppi.

Fourth, you can surely check image’s ppi with Photoshop. For that you need to open the image and click and hold Document Sizes in status bar. But if the image doesn’t contain information about physical extents, Photoshop displays 72 ppi nevertheless.

Alternatively, you can use ImageMagick, which displays physical extents only if they are present:

$ identify -verbose img.png | grep pHYs
    png:pHYs: x_res=5669, y_res=5669, units=1
$ echo '5669 * 0.0254' | bc
143.9926

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