Hey there I was wondering why is it when I zoom into an image I took it looks grainy & pixalated. The image will be taken at an iso of 100 and look sharp on the the camera but not as sharp on a tablet or computer been it appears larger. My camera is Nikon Z6.
Any time you zoom in image quality will look worse than when you're not zoomed in. It's like holding a magnifying glass up to a postage stamp or a photo printed in a newspaper. What looked like solid lines or areas of solid colors when you viewed them from normal distance and they were unmagnified are shown to actually be a series of very small dots instead.
This was true of prints made from film negatives. If one looks just as closely at a 16x20 inch print made from the same negative as an 8x10 inch print, it will always be easier to see defects in the 16x20 than in the 8x10 due to the greater enlargement.
It's still true when viewing digital images.
When you increase the enlargement of an image to 100% (one image pixel = one screen pixel), noise that got averaged away when it was scaled to fit the entire image on your screen will be visible when every pixel in the image is displayed using one pixel on the screen.
The more you enlarge an image, the more you will be able to see some parts of the image that looked sharp at smaller viewing sizes are actually slightly blurry. This is why depth of field for the exact same image is reduced when viewed at larger size from the same distance. There's only one distance that is focused the sharpest. Everything else gets blurrier and blurrier the further in front of or behind the focus distance they are. The more we magnify an image, the easier it is to see that things slightly in front of or slightly behind the actual focus distance are blurry rather than sharp.
Also, when you view images at 100% magnification, the more pixels an image has, the more you are enlarging each pixel to view it at 1 image pixel = one screen pixel. If you have two images that were taken with the same sized sensor and one is 20 MP and the other is 40 MP, you are enlarging the second image by twice as much, in terms of area (and 1.414X as much in linear terms) as you are enlarging the first image.
If you view images at greater than 100%, you're actually stretching the image so that each image pixel is repeated on several adjacent screen pixels, so it will really start to look pixilated and blocky.
Your Nikon Z6 has a 24.5 MP sensor. If you were used to a lower resolution camera, when you magnify the images from the Z6 to "100%" (so that one image pixel is displayed by one screen pixel) you're increasing the magnification more than you were with the previous lower resolution camera.