How do I display imported images at actual size?

Question

I know that this is an extremely basic question, but I am having a lot of trouble finding the answer in the documentation.

When I import an image (for example, Import[test.png]), Mathematica often displays it smaller than the actual size of the image. How do I force Mathematica to display the imported image at actual size?

I may want to display such images using Grid. For example, suppose that fname is a list of *.png file names. Then I may want to import and display all of those images using a command like:

fname = FileNames["*.png"];
table = Transpose[{fname, Table[Import[fname[[i]]], {i, 1, Length[fname]}]}];
Grid[table]

and I'd like the images displayed at actual size.

I know that this is a very basic question, but I really appreciate your time.

Answer 1

Programmatically I would use:

img = ExampleData[{"TestImage", "Lena"}];

Image[img, Magnification -> 1]

Manually you can right-click on the image and select Actual Size.

---

Within an Image there is raster data of a particular dimension:

Dimensions @ ImageData @ img

{512, 512, 3}

This is a 512 x 512 pixel image with three channels. Additionally the Image has options:

Options[img]

{ColorSpace -> "RGB", ImageSize -> Automatic, Interleaving -> True, Magnification -> Automatic}

The two options that control the displayed image size are ImageSize and Magnification.

When you use the the context menu to set Actual Size you remove (reset) the Magnification option and set ImageSize -> All. If you select a Magnification level you set ImageSize -> All and a Magnification value.

When you change the size of an image interactively by dragging the corners of the bounding box you remove (reset) the Magnification option an set a specific ImageSize value, e.g. ImageSize -> {171., Automatic}.

When you select Automatic Size you remove (reset) both options.

If numeric values for both options are given within Image the magnification is ignored:

Image[img, Magnification -> 40, ImageSize -> 200]

The Magnification option can also be used outside of Image, and it does not work the same as when it is set inside Image.

When used inside it prevents automatic scaling of the image, and it combines with Notebook magnification meaning that using Image[img, Magnification -> 2] inside a Notebook with magnification 50% produces a 1:1 image.

When used in Style as in Style[img, Magnification -> 2] it does not prevent automatic scaling of the image to fit the window if the two options within Image are either Automatic or not present. Further, this magnification level overrides the Notebook magnification rather than combining with it, but combines with the Image setting.

One may display the image raster 1:1 regardless of Notebook zoom for an arbitrary image using:

Style[Image[img, ImageSize -> All, Magnification -> 1], Magnification -> 1]

Answer 2

I guess:

i = ExampleData[{"TestImage", "Lena"}]; 
Image[#, ImageSize -> ImageDimensions[#]] &@i

will do.