The Truth About Image Sharpness & Color Depth – Raw vs Jpeg
Updated: Sep 18, 2020
Photographers are notorious for obsessing about image sharpness. We like to look at pixels forensically, as though we are studying cells.
Image sharpness is more about perception. If you zoom down deep enough nothing is sharp. A single pixel is worth a thousand words if you can find the words.
Your computer monitor will affect your perception of image sharpness. A 720p monitor runs at about 54 ppi (pixels per inch). A 1080p monitor runs at about 81 ppi and a 4K monitor runs at about 163 ppi. Higher-end monitors will have better visual resolution (images will appear sharper and more vivid) but you can’t cheat physics. 54 ppi is 54 ppi, no matter how you slice it.
Jpeg images are compressed images. Your camera does this automatically – you do not have a choice and they are recorded at 72 ppi. What this ultimately means is that if you are using a 1080p monitor then your images will appear roughly as sharp as they will appear on a print at a scale of 1:1. Unfortunately, no matter what the resolution of your monitor is, 72 ppi will never resolve higher than 72 ppi.
Tip - To view your images at 1:1 (1 inch screen = 1 inch actual) in Adobe Photoshop turn on the rulers (Ctrl-R). As a starting point for a 6000x4000 pixel image (24MP) set the image zoom to 36%. You can physically measure one inch on your monitor and adjust the zoom as needed.
Another major limitation of a jpeg image is color depth. Jpeg images are recorded as 8-bit color images. I will cover this in more detail in a future blog but what this means is that 8-bit images capture 256 colors for each primary color (RGB - 2x2x2x2x2x2x2x2 (8) = 256). 256R x 256G x 256B = 16.7 million colors – sounds like a lot but its not. 256 colors for each primary color is not much. Each pixel is only one color. Once you start adjusting contrast any areas of uniform color, particularly in skies and gray areas, you will start to notice banding and image degradation.
Jpeg files are great for on-line images but if you plan to print your images then you will need to consider working with RAW files.
RAW files are recorded at 300 ppi and between 12-bit and 14-bit color depth. When imported into most photo editing software, 12-bit or 14-bit images are up-sampled into 16-bit files. Now the dynamics change considerably. Even if you are using a 4K monitor, you image will be less sharp on screen than it actually is. A 4K monitor will resolve images no higher than about 163 ppi even though a RAW image is 300 ppi.
As far as your photo editing software is concerned, your image is 300 ppi. In other words, your image, as sharp as it appears on screen, is actually quite a bit sharper. Not only that, a 16-bit RAW image records 65,536 colors per primary color (RGB - 2x2x2x2x2x2x2x2x2x2x2x2x2x2x2x2 (16) = 65,536). 65,536R x 65,536G x 65,536B = 28.1 billion colors – yes that’s billion!
As you can see in the illustration above, the 16-bit color strip is absent of banding and the transitions of color are significantly smoother. The more adjustments you make (contrast, etc.) on an 8-bit image, the more noticeable the banding and image deterioration will be. 16-bit RAW images are far more resistant to deterioration because of the higher resolution and quantity of color variations.
If the math confuses you a bit, then just remember this; RAW files are 4.2 times sharper and contain 1682 times as many colors as jpeg images. These are technical observations. In real life things are not so clear-cut. If your images are out of focus, there’s not much you can do. Also, lens quality / f-stop setting will affect sharpness.
-Importing RAW files into Adobe Photoshop
-Re-sizing images properly for printing
-Using Adobe Camera Raw
-sRGB vs Adobe RGB
- and more…..