Why is image shown at 100% smaller on screen

Thank you for the clarification.

Resolution (ppi) is ignored in Photoshop’s display.

Are you sure that banner have 72 pixels per inch resolution? From your description image is placed in Photoshop using Place command and about 1/4 of the real dimensions. This reminds me on Photoshop's default behavior for images with a different resolution of document resolution.

This sounds like 300ppi image 300x250px placed in document with 72 ppi. In this scenario, the image will be placed at 72x60px.

Photoshop has always displayed image size literally, as gener7/Gene described. As you use displays with higher resolution, the same pixel dimensions appear smaller. Other image editing programs do the same thing.

Web browsers define 100% using a method that tries to keep apparent pixel dimensions consistent across different screen resolutions. If you are using a Retina/HiDPI display, my guess is that the 300 x 250 pixel image measures at least 600 x 500 screen pixels when shown in a web browser. You can see the effect yourself. Open the 300 x 250 pixel image in any web browser, take a screen shot of the image in the browser, and measure the screen shot of the image in pixels.

Photoshop at 100% magnification shows the image at exactly 300 x 250 screen pixels.

Both the web browser and Photoshop are doing the right thing, because both definitions of 100% are useful for different purposes. To make Photoshop look more like the web browser, you can choose 200% magnification.

In cases of a Retina or hidpi display, images are not scaled in Photoshop as in a browser. At 100%, one image pixel = to one screen pixel as displayed in Photoshop.

Of course we would need to know exactly what you have.

* Adobe product and version number

* Operating system and version number

* Display resolution, for example 1280 x 800

Gene