Resolution and Image Size
Written by Abin Alex and Anu Joseph.
Abstract
Resolution is the amount of detail an image holds, counted in pixels, and the pixel count sets how large a picture can be shown or printed before it looks soft. This guide defines the pixel, the megapixel and pixel pitch, separates PPI from DPI, and estimates how much resolution a given use needs. It argues that more pixels help only when the lens, the light and the pixel size support them, so more megapixels do not by themselves mean a better camera. It also explains what happens when an image is resized. It is written for photographers and cinematographers.
Keywords: resolution; megapixel; pixel pitch; PPI; DPI
What is a pixel?
Short answer. A pixel is the smallest unit of a digital image. Each pixel stores one colour and one brightness value, and thousands of them side by side form the picture.
- A camera sensor records light with a grid of photosites. The processed image file then holds one pixel for each sample.
- Image size is written as width by height in pixels, for example 6000 × 4000.
- Pixels have no fixed physical size. The size depends on the screen or the print they are shown on.
- More pixels give a finer grid, so edges and small details are drawn more smoothly.
Cham tipSay image size in pixels, not in inches. Inches only exist after you choose a print size.
Cham taskOpen a photo on your computer and check its size in pixels. Write down the width and the height.
Check yourself: What does the size 6000 × 4000 mean?
The image is 6000 pixels wide and 4000 pixels high.
What is a megapixel?
Short answer. A megapixel is one million pixels. Multiply the width by the height in pixels and divide by one million to get the megapixel count.
- 6000 × 4000 pixels is 24 000 000 pixels, or 24 megapixels (MP).
- Doubling the megapixels does not double the width. To double the width and height, you need four times the megapixels.
- Megapixels tell you the pixel count only. They do not tell you the quality of each pixel.
| Image size | Pixels | Megapixels |
|---|---|---|
| 1920 × 1080 (Full HD) | 2 073 600 | 2.1 MP |
| 3840 × 2160 (UHD 4K) | 8 294 400 | 8.3 MP |
| 4000 × 3000 | 12 000 000 | 12 MP |
| 6000 × 4000 | 24 000 000 | 24 MP |
| 8000 × 6000 | 48 000 000 | 48 MP |
| 7680 × 4320 (8K) | 33 177 600 | 33.2 MP |
Table 1. Common image sizes and their megapixel count (calculated from width × height).
Cham tipDo the sum yourself: width × height ÷ 1 000 000.
Cham taskFind the megapixel count of your phone photo and of a screenshot. Use the width × height sum.
Check yourself: How many megapixels is a 4000 × 3000 image?
12 megapixels.
What is pixel pitch and why does it matter?
Short answer. Pixel pitch is the distance between the centres of two neighbouring pixels on the sensor, usually written in micrometres (µm). A larger pitch means a larger pixel, which collects more light.
- Pitch is the sensor width divided by the number of pixels across. A full-frame sensor 36 mm wide with 6000 pixels across has a pitch of 36 mm ÷ 6000 = 6 µm.
- A phone sensor is far smaller. A 48 MP phone sensor packs many pixels into a tiny area, so each pixel is much smaller than 6 µm.
- Larger pixels collect more light, which usually means less noise in dim scenes (Nakamura, 2006).
- This is why a 24 MP full-frame camera often handles low light better than a 48 MP phone, even though the phone has more pixels.
- The Camera Sensor guide explains pixel size and sensor size in more detail.
Cham tipWhen you compare cameras, look at pixel pitch and sensor size, not just the megapixel number.
Cham taskFind the sensor width and the pixel width of your camera. Divide the width by the pixel count to get the pitch.
Check yourself: Which has the larger pixels: 24 MP on full frame or 48 MP on a phone?
The 24 MP full-frame sensor, because its sensor area is much larger.
What is the difference between PPI and DPI?
Short answer. PPI, pixels per inch, describes how many pixels fall in one inch of an image or a screen. DPI, dots per inch, describes how many ink dots a printer puts in one inch.
- PPI belongs to the image and the screen. DPI belongs to the printer.
- A common print target is 300 PPI for sharp prints viewed close up.
- Print size in inches = pixels ÷ PPI. A 6000 × 4000 image at 300 PPI prints at 20 × 13.3 inches.
- Changing the PPI number in a file does not add detail. It only changes the print size the file claims.
| Image size | Print size at 300 PPI | Print size at 150 PPI |
|---|---|---|
| 4000 × 3000 (12 MP) | 13.3 × 10 in | 26.7 × 20 in |
| 6000 × 4000 (24 MP) | 20 × 13.3 in | 40 × 26.7 in |
| 8000 × 6000 (48 MP) | 26.7 × 20 in | 53.3 × 40 in |
Table 2. Print size = pixels ÷ PPI (calculated).
Cham tipWork out the print size from pixels ÷ PPI before you order a big print.
Cham taskPick a photo and find the largest print it can make at 300 PPI and at 150 PPI.
Check yourself: A 3000 × 2000 image is printed at 300 PPI. How large is the print?
10 × 6.7 inches.
How much resolution do you need?
Short answer. It depends on the output and the viewing distance. Screens need few pixels. Prints need more. Billboards need the fewest per inch because people see them from far away.
- Screens: Full HD needs about 2 MP and UHD 4K about 8 MP. Anything larger is downsized for display.
- Prints seen at arm's length need about 300 PPI. A larger print viewed from further away can use 150 PPI or less.
- Billboards are viewed from many metres away, so they can use very low PPI. Detail the eye cannot resolve at that distance is wasted.
- Social media platforms resize and compress uploads, so a very large file does not look better there.
| Use | Typical need | Why |
|---|---|---|
| Phone and web | 1–3 MP | Screen is small and files are downsized |
| 4K TV | 8.3 MP | Screen has 3840 × 2160 pixels |
| A4 print | About 9 MP at 300 PPI | Viewed close up |
| Large poster | Lower PPI is acceptable | Viewed from a distance |
| Billboard | Lowest PPI of all | Viewed from far |
Table 3. Resolution needs by use (screen figures are calculated from the pixel sizes; print figures follow the 300 PPI rule).
Cham tipAsk first: where will it be seen, and from how far? Then pick the pixels.
Cham taskExport one photo for the web (2000 px wide) and for an A4 print (3500 px wide). Compare file sizes.
Check yourself: Does a billboard need 300 PPI?
No. It is viewed from far away, so it needs far fewer pixels per inch.
Does more megapixels mean a better camera?
Short answer. No. Megapixels show how many pixels a camera records, not how good they are. Lens quality, pixel size, light and image processing decide the final quality.
- A sharp lens matters more than extra pixels. A soft lens cannot give the sensor more detail than it receives.
- More pixels on the same sensor mean smaller pixels. They collect less light each, so noise can rise in dim scenes.
- More pixels give bigger files that fill cards and drives faster and slow your computer.
- Extra pixels help when you crop heavily or print large, so choose the count that matches your work.
- Camera makers use pixel binning on phones to combine neighbouring pixels into one larger pixel for low light.
Cham tipTest, do not trust the number. Shoot the same scene on two cameras and compare at 100 per cent.
Cham taskShoot the same scene at the full resolution and at half resolution. Compare both at 100 per cent zoom.
Check yourself: Name two things other than megapixels that decide image quality.
The lens and the pixel size. Light and processing also matter.
What happens when you resize an image?
Short answer. Making an image smaller discards pixels and usually looks fine. Making it larger invents new pixels by guessing, and the picture looks soft. Resolution and file size grow together.
- Shrinking, called downsampling, keeps most of the visible detail for screen use.
- Enlarging, called upsampling, adds no new detail. Software only smooths the gaps between pixels.
- An uncompressed 24-bit colour image takes 3 bytes per pixel. A 24 MP image is about 72 MB before compression.
- JPEG compression cuts the file size a lot, but heavy compression adds blocky artefacts.
- Crop first, resize later, and always keep the original file.
Cham tipNever upsize a small file for a big print. Reshoot with more pixels or choose a smaller print.
Cham taskEnlarge a 1000 px photo to 4000 px and compare it with a real 4000 px photo of the same subject.
Check yourself: Does enlarging a photo in software add detail?
No. It only guesses the new pixels, so the picture looks soft.
Questions beginners ask
What is resolution in photography?
Resolution is the amount of detail in an image, counted in pixels. A 6000 × 4000 image has 24 million pixels.
How do I calculate megapixels?
Multiply the width by the height in pixels and divide by one million. For example, 6000 × 4000 = 24 000 000, which is 24 MP.
What is pixel pitch?
Pixel pitch is the distance between the centres of two neighbouring pixels on the sensor. A larger pitch means a larger pixel that collects more light.
What is the difference between PPI and DPI?
PPI counts pixels per inch in an image or screen. DPI counts printer dots per inch.
How many pixels do I need for a print?
Multiply the print size in inches by the PPI you want. At 300 PPI, an 8 × 10 inch print needs 2400 × 3000 pixels.
Is a 48 MP phone better than a 24 MP camera?
Not always. The larger pixels of a bigger sensor collect more light, so a 24 MP full-frame camera often gives cleaner low-light images.
References
- Nakamura, J. (ed.) (2006) Image Sensors and Signal Processing for Digital Still Cameras. Boca Raton: CRC Press.
How to cite this guide. Alex, A., & Joseph, A. (2026). Resolution and image size: A guide for photographers and cinematographers. Creative Hut Academy. https://creativehut.org/library/resolution-and-image-size/
Make this your craft at Creative Hut Academy
Creative Hut Academy in Mattakkara, Kottayam, Kerala teaches photography, cinematography, editing, sound and AI filmmaking in one-year residential diplomas. Students come from across India.
Want to talk? Message us on WhatsApp, or ask Cham, our AI mentor, a study doubt.