Pixelcalculator
sponsored by: Dia Foto Film Scannen www.archivscan.ch
Formulas
Calculation of length or width, pixels and DPI with the following specifications:
| Image: | 3266×2449 Pixel (8Mpx, 4:3) |
| Print size: | 277 × 207 mm |
| Pixel density: | 300dpi |
\( Length[mm] = {pix × 1 in [25.4mm] \over dpi}\)
\(Pixel = {dpi × mm \over 1 in [25.4mm]}\)
\(dpi = {pix × 1 in [25.4mm] \over mm}\)
\(Bytes = { \over 8 bit [1 Byte]} = {(1000px · 2000px) × 24 \over 8 bit × 1M} = 6MB\)
Examples
I want to print a picture for the photo album, 13 x 18 cm, with good quality. How big does the resolution have to be in pixels?
A good quality picture for a photo album is printed at 300 dpi. To calculate the resolution in megapixels, multiply the number of pixels of length and width and divide them by mega (1 million).
\(Pixel X = {300dpi × 13mm \over 25.4mm} = 1535 pix\)
\(Pixel Y = {300dpi × 18mm \over 25.4mm} = 2126 pix\)
\(Resolution = {1535 × 2126 \over 1`000`000} = 3.3 Mpx\)
I have an image with 3264 x 2448 pixels and would like to print it as a poster. How big can I print the poster?
In contrast to a small picture in the photo album, the poster does not have to have a high pixel density, as this is viewed from a greater distance and the pixels become smaller for the eye. Approx. 100 dpi is recommended for a poster.
\(Length = {3264pix × 2.54cm \over 100dpi} = 83 cm\)
\(Width = {2448pix × 2.54cm \over 100dpi} = 62 cm\)
I would like to scan slides and present them with a slide show on the television. Screen TV 40 inches; Resolution: 1,920 x 1,080 pixels. How big does the scan resolution have to be?
The dimensions of a slide are 36 x 24 mm, so the aspect ratio does not match that of the television (television = 16: 9 slide = 3: 2). We only calculate the pixel density of the height of the image, as this is the limiting measure.
\(dpi = {1080pix × 25.4mm \over 24mm} = 1143 dpi\)
Resulting image size horizontally in the correct aspect ratio:
\(pixel = {1143dpi × 36mm \over 25.4mm} = 1620 pixel\)
I would like to print a poster of 900 x 600 mm with the maximum resolution from a slide. How good will the quality be in "dpi"?
The maximum resolution of the scanner is 4000dpi, a slide has the dimensions of 36 x 24 mm. After you have calculated the number of pixels, you can use the dimensions of the poster to calculate the pixel density.
\(Pixel = {4000dpi × 36mm \over 25.4mm} = 5669 Pixel\)
\(dpi = {5669pix × 25.4mm \over 900mm} = 160 dpi\)
Units
| engl. unit of length | 1 Inch = 25.4 mm |
| dots per inch | 1 dpi = 1 Dot per Inche(25.4 mm) |
| pixel per inch | 1 ppi = 1 Pixel per Inch(25.4 mm) |
| digital unit of measurement | B = Byte
1 bit = 0 | 1 1 B = 8 bit 1 kB = 1024 B 1 MB = 1024 kB |