Music, art & photography · course 94 of 105

Image Resolution From Pixels to Print

Work out the numbers behind any digital image: megapixels, aspect ratios, how big a print the pixels make at a given PPI, the largest crop to a ratio, and file size in MB and MiB.

4 modules

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Runs in Claude (claude.ai, the Claude apps or Claude Code) with your own Claude account. A course opens there as soon as your payment goes through; nothing is shipped.

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What it teaches

The numbers behind a digital image. Pixel count and megapixels, aspect ratios (3:2, 16:9, and how to reduce any width:height), how big a print a given number of pixels makes at a stated PPI (pixels per inch) and how many pixels a print needs, the largest crop to a ratio, resizing without distorting, and the size of an uncompressed image in bytes, megabytes (MB) and mebibytes (MiB). The AI asks 3 questions, places you, shows a short card per module, then gives you one question at a time.

Not a camera or editing course, and it can’t judge whether your own print will look sharp.

How long

42 items. About 12-22 rounds for a confident student up to about 50-55 for a beginner who misses a lot, plus a 12-item final: 1-2 sessions (estimate, not timed with a real student). The tutor gives a one-line save code at the end of each session.

From the answer key · M1, row P6

An image is 1920 × 1080 pixels. What is its aspect ratio in lowest terms (whole numbers with no common factor)?

Think first, then show the answer

Answer16:9

Working1920:1080; the greatest common divisor of 1920 and 1080 is 120; ÷ 120 = 16:9.

The wrong answer it catches9:16 → swapped: an aspect ratio is width:height, and this frame is wider than it is tall.

Aspect ratio: “The aspect ratio of an image is the ratio of its width to its height. It is expressed as two numbers separated by a colon, in the format width:height.” This course writes an image size width × height: 3000 × 2000 is 3000 wide and 2000 tall.
Lowest terms: divide both numbers by their greatest common divisor (the biggest whole number that divides both). Example: 640:480, divided by 160, is 4:3.

The modules

4 modules, drilled one item at a time.

M0
The words
The words: pixel, megapixel, PPI and DPI, aspect ratio, scaling
M1
Megapixels and aspect ratios
Megapixels from width and height, aspect ratios in lowest terms, finding a missing side of a ratio
M2
Print size from pixels and PPI
Print size from pixels and PPI, pixels a print needs, and the PPI a print works out to
M3
Crop, resize and uncompressed file size
The largest crop to a ratio, resizing without distortion, and an uncompressed image’s size in bytes, MB and MiB

Before it teaches, it asks

1
What do you do with images most (photography, design, print, web, nothing yet), and do you know your camera’s megapixels?
2
An image is 6000 × 4000 pixels. What is its aspect ratio in lowest terms (whole numbers with no common factor)?
3
An image is 3000 pixels wide. Printed at 300 PPI, how many inches wide is the print?

What’s exact, and what isn’t

Show

Straight from the course’s own notes.

Words from six saved pages, read 2026-10-12: Wikipedia’s “Pixel”, “Pixel density” (the page “Pixels per inch” leads to), “Aspect ratio (image)”, “Image scaling” and “Color depth”, and NIST’s page on the IEC binary prefixes (MiB and MB). A script checks all 25 quotes word for word on the saved copies and fails if any page or quote changes; it does not re-fetch the live pages.
Computed by script: Every M1, M2 and M3 key and every number in a Working, in exact fractions; rounding is half-up and a script refuses a case that lands exactly on a tie. All 28 listed wrong answers are recomputed from the slip they name and checked to differ from the key. The M0 Answers are not computed: each is built from quotes, and a script checks that its key phrases and numbers sit in the quotes listed for it.
The course's own conventions (the cards say so): A ratio “in lowest terms” means both numbers divided by their greatest common divisor; the largest crop to a ratio keeps the photo’s full width or full height; an “uncompressed 8-bit RGB image” takes width × height × 3 bytes with no header; every question that needs a PPI states it. These are arithmetic rules, not claims from the sources.
Honest limits: The course drills quoted definitions and arithmetic. It never says which PPI or size is right for a job, and it can’t tell whether a real print will look sharp. A megapixel here is exactly one million pixels worked out from an image’s own width and height; the Pixel page notes that camera specifications may distinguish total sensor pixels from the effective pixels of the recorded image, which the course does not touch. Real JPEG and PNG files are compressed; the course never computes their size. Inches only.
Not in it yet: Centimetres and millimetres, sensor size and crop factor, printer dpi and halftone screens beyond the definition, CMYK and colour depths other than 8-bit RGB, compressed file sizes, video pixel aspect ratios, AI upscaling.