Image resolution issue

When I resize it to 4800 x 3200 the effective ppi drops to 180 and it says that it has scaled to 166.7%, but it's still smaller than it's original size of 12000 x 8000.

To get a 300ppi matching Effective resolution, you would have to upsample the scale in Photoshop—you can’t upsample an image in InDesign. Upsampling doesn’t typically get you any visible quality change in print, but if you sampled up to 503, the Effective res in InDesign would be 300ppi:

Pixels are not. unit in InDesign. There is a ruler unit called pixels, but it is misnamed and should be called points.

Your 12,000 x 8,000 pixel image is indeed that size in pixels. But because the resolution is 300 ppi it imports at 40 x 26.67 inches. InDesign knows the image is 12,000 x 8,000 but it imports it according to your pixel size. If you ask the rulers to display pixels they will asum 72 pixels per inch for everything, so your 40 x 26.67 inch image will appear to be 40*72 pixels x 26.67*72 pixels, or 2,880 x 1,920 pixels. Its effective resoltuion is 300 pixels per inch.

When you scaled it up to 167% You made the image bigger, so you made the pixels bigger. They used to be 1/300 inch (hence 300 pixels per inch or PPI). You made them larger so they are now 1/180 inch.

To elaborate:

12000 x 8000 @300ppi

Your measurement in InDesign is in Pixels - not mm/inches

When you placed your image - InDesign is using postscript inches for the pixel size - which is 72ppi

12000/300(*72) gives you 2880

and I presume for the height you also meant 1920 - not 192

again 8000/300(*72) gives you 1920 

That's why your image is coming in the 'wrong size'.

To fix - you need to resize your InDesign document - and use mm or inches and the exact size you are outputting.

12000 px wide at 300 ppi would be 40 inches

Divide 12000/300 = 40 

is that the width of your banner?

about 3.3 feet wide?

You are mixing measurement worlds here and it can get a bit confusing.

How did you create a New Document?

Since you are creating, ultimately, a print document, you should have selected a Print preset (which assumes 300dpi as default resolution), in which case your banner's dimensions should have been input in print-based units such as inches: therefore a document 40" wide x 26.66" high if that's your final size of the banner.

If you input your dimension as pixels (or select a Web preset), ID assumes it will be a screen-based document and therefore assumes 72 dpi.

If you create a New Document in inches, and THEN drop your image, you will see it's placed appropriately.

(btw: If you change your current document's Units to Inches, you will find you now have a document that's 166.66" wide. That's certainly not what you want.)