A few scanning tips


Calculate Maximum Image Size Dimensions and print size
from camera Megapixels and Aspect Ratio

What are the maximum image dimensions in pixels that can fit in X megapixels?

How large can we print it?

What image size do we get with any 50 megapixel image?

The dimensions of its shape depend on the Aspect Ratio.

These common Aspect Ratios can be entered in standard nominal format:
1:1 = a square image (image width same as height)
4:3 = 1.333:1 - Typical of compact camera and cell phone images
3:2 = 1.5:1 - Typical of DSLR camera images, and 35 mm film
16:9 = 1.778:1 - HDTV and camera video, typically 1920x1080 or 1280x720 pixels

The aspect ratio of the camera image and of the camera sensor are the same when straight out of the camera, but will be different if the image has been processed and cropped to a different shape (or if printed on paper, which is usually another shape).

Aspect Ratio is usually a rounded approximate nominal value. Or preferably more precise, it can be the exact corresponding divided number (image width/height, dimensioned as pixels or known mm or inches) like the 1.5 or 1.3333 or 1.7778 ratio. Example: for 4:3 aspect, 4/3 = 1.3333. But it can be the more exact number, like maybe 1.327:1. It is Not necessary to enter the :1 here (:1 is assumed if not), but you can enter it or not, or you can enter the format like 4:3. For an actual real sensor, the actual precise value (like 1.327 or 1.503) may compute more precisely. More about aspect ratios.

Aspect Ratio Format — Example:

Aspect ratio 4:3 is 4/3 = 1.333, which can be entered here as:

4:3 or 1.333:1 or 1.333, or as 1.338 if and when more precise.

Or 4288×2848 pixels is 4288/2848 = 1.5056:1 (images).
Or 17.3x13 mm is 17.3/13 = 1.331:1 (sensors or film).
Or 4x5 inches is 5/4 = 1.25:1 (prints).

The calculator will show the precise format, as like 1.3315:1 format.

The calculator below shows your requested aspect ratio, and also automatically adds results for a few standard aspect ratios (1:1, 4:3, 3:2, 16:9). These rounded nominal values may not precisely match your sensor dimensions, but your first request can use an Aspect Ratio more precise than the nominal 3:2 or 4:3.

Megapixels are exactly computed by image dimensions in pixels, megapixels = Width × Height. 6000×4000 = 24,000,000 pixels, = 24 megapixels. Megapixels use the conventional 1K = 1000, and NOT the 1K = 1024 used by memory chips.
Aspect Ratio is exactly computed by image dimensions in pixels, Aspect Ratio = Width / Height. 6048 / 4024 is 1.503 : 1.
Your results will come out closer if entering your actual real numbers instead of the rounded camera specifications.

But there are ifs and buts about everything, so this is trying to explain why the result megapixels may not exactly match your camera's specified megapixels. Three values of pixel dimensions may be shown, in the order of:

1. Exact computed dimensions (matches specified megapixels exactly, even if a pixel cannot be fractional). Aspect Ratio can be entered in formats such as 1.3333 or as 4:3

2. So dimensions are also rounded to whole pixels, necessary for real pixels, but which changes megapixels a little. One pixel difference of width might affect a few thousand rows of height.

3. Cameras create pixel dimensions that are evenly divisible by 8 (I will call it Div8, and is only size shown if already Div8 is specified). But resampled or cropped images might have any dimensions, likely Not divisible by 8.

Maximum Image Dimensions
and Print Size from Megapixels

Megapixels    Aspect Ratio

Image Size x pixels (reverse direction)

If printed at dpi (Optional)    

Div8 Images resized in photo editors can be any dimensions, but camera sensors actually use pixel dimensions which are evenly divisible by 8, no doubt to match the JPG 8x8 compression blocks (I'll call that value Div8 here). Image pixel dimensions created by the actual camera are optimally Div8, however specifications for megapixels or aspect ratio are rounded. But pixel dimensions of images cropped or resampled in your editor have low odds to be evenly divisible by 8 (which still works).

There are two calculator options, and the results for each case are:

Otherwise, Megapixels will work fine, and even better if you enter accurate higher precision for the actual megapixels and aspect ratio. Since pixel dimensions are typically four significant digits, then to reach that same four-digit precision again, enter all values to at least four significant digits, if applicable. Four digits total are usually enough, but sometimes five digits can be better on Aspect Ratio. The Image Size option does compute sufficient precision from your dimensions. You can see in the initial default example, that 1.503 computes better than the nominal 1.5 below it (unless 1.5 happens to be the actual precise value).

This blue image shows the aspect concept visually. 4:3 is taller, but 3:2 is wider. The sensors all try to fit their diagonal to the lens diameter. However, the 16:9 video mode frames in photo cameras are normally necessarily contained within the dimensions of the existing 4:3 or 3:2 photo sensors. Then 16:9 cannot be the full diagonal (that video width cannot be wider than the sensor width). But their size is likely even a little smaller to optimize the subsampling, because 16:9 HD movies are typically output as 1280x720 or 1920x1080 pixels, which is 0.92 or 2.07 megapixels. Actual camcorder camera sensors are 16:9, and any 4:3 photo image must fit into that. Since specifics are not known here, 16:9 is computed on this page as a camcorder, independent of any still frame size. See More about maximum video frame sizes relative to still pictures.

Again, camera megapixels and aspect ratio are said as nominal rounded values. But these two values are just a multiplication and a division of the pixel dimensions, and as explanation of the precision offered, the second Image Size option was added to show those actual more precise computed values. They also show the difference from the nearest standard nominal aspect ratio (if in range). The few tenths of a percent of difference is not a big deal in practice. See the Aspect Ratio page.

The goal is to compute maximum dimensions of a specific aspect ratio that matches the specified megapixels. Megapixels is sensor Area (in units of pixels). Pixels are the only units used. The calculator computes the Width x Height image pixel dimensions of various aspect ratios that match the megapixels that you specify.

The terms kilobytes and megabytes and gigabytes were corrupted to mean multiples of 1024 bytes, necessarily used for memory chip sizes (including memory cards, USB flash drives and SSD, which are all memory chips which truely use 1024 byte units that are required by memory addressing). But sadly, computer operating systems commonly use the 1024 base for file sizes, which is unnecessary and counter-productive. The standard SI term mega means millions, defined as multiples of 1000. So mega in megapixels still correctly means 1000s, same way as humans count things. Same true also for manufacturer's hard disk specifications in gigabytes (units of 1000s), except our computer operating systems still sadly also refer to size of hard drives and files as multiples of 1024, but which do not use memory binary addressing, so no 1024 complications. A 4 GB hard drive is sold as 4,000,000,000 bytes, which the operating system calls 3.725 GB, but which in fact is in fact exactly 4,000,000 bytes. The term mega is correctly units of 1000, except actual memory devices do their own thing, necessarily using 1024 units.

Math is precise, but Real World is sometimes less so: If checking the calculator against your camera, realize that cameras round their specifications, which affects precise calculations. For example, a Nikon D800 camera specifies 36.3 megapixels and we assume a DSLR nominal 3:2 aspect ratio. That computes 7376 x 4920 image size. Close, but its actual is 7360x4912 pixels which computes 36.152 megapixels and 1.498 aspect ratio, which does then compute the correct image size. If you enter the actual correct numbers, the calculator should show the exact dimensions.

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