Pixels, Printers, Video
What's With That?

These basics are pretty much about the single issue: How do I use my image, how to I make it be the proper size for viewing, for printing, or for the video monitor? All this is really quite easy, but digital may just be a new concept. It is like learning to drive - once you learn an easy thing or two, it's a skill helpful for life. When you know, you will simply just know. But yes, it does seem that we could subtitle this: Details that no beginner wants to know. However the point is: You'll never grasp digital images until you get it ... until you know what digital images are, what to do with them, and how to do it.

Seriously, once we accept that pixels actually exist, then all this stuff is rather easy. It's about pixels.

We just gotta know about pixels, and if any mystery, a very short primer is here: What is a Digital Image Anyway?

This page tries to be a quick summary of the digital concepts, about how things work. The answer to virtually any question about image size starts with one of these basics. To be able to use digital images well, we need this understanding. This may perhaps be written a little like an argument, refuting the dumb incorrect myths we may have heard about how digital works. The concepts below are instead what you need to know to use digital images properly. It is actually rather easy to grasp, if you get started right.

The Most Fundamental Digital Concepts

The size of an image might be, for example, 4000x3000 pixels. That is 4000x3000 = 12 megapixels. Or, 4288x2848 is also 12 megapixels (4:3 vs 3:2 aspect ratio). We tend to think of this as the "resolution" of the image. The pixels do indicate the "fineness" of the smallest possible digital detail (a pixel, which is a dot of one color). This example is borrowed from the image Resize page, to show the idea about pixels.

400x500 pixels, 0.2 megapixels

The concept of pixels: This is an enlarged view of a tiny 58x58 pixel area of this picture (at arrow near center), shown at 800% size to be able to see the pixels.

Pixels are how digital reproduces a scene and its colors. The camera lens creates an image. To reproduce that image digitally, the digital camera sensor merely takes many color samples (each is a pixel), of many very tiny areas of the image, in this way shown. Film uses tiny specks of silver or emulsion dyes instead of pixels, which is not digital numbers, but film does the same sampling idea (colors of many tiny areas). Film areas actually show the color, which we can see. However, digital is totally about pixels, which are simply numbers representing the color. For example, the reddest orchids above have RGB components of about RGB(220, 6, 136), each on a scale of [0..255], so the RGB components of it are red is bright, green is weak, blue about mid-range. This color describes that shade of bluish red in one tiny area, a pixel. We don't have to know much detail, but more is at Wikipedia about the RGB color system.

The main concept of digital is that each pixel is just NUMBERS, binary data describing ONE RGB COLOR of one tiny area, a tiny dot of color, much like one small colored tile in a mosaic tile picture. The numeric concept may be new today (called digital), but the tile concept is at least 5000 years old. A pixel that is pink has the similar effect as a small piece of tile the same shade of pink. Our brain recognizes the reproduced image in those pixels or tiles. But enlarge these enough, and all you will see is the pixels or the individual tiles. Pixels are all there is in a digital image, and we must think of it that way. Ignoring them will Not grasp the concept. Digital will make sense when you do think of pixels.

The concept is that the "photo detail" that we perceive in a digitally reproduced picture is entirely due to the color differences in the pixels. A pixel is simply a color description. Color is the detail. Pixels show the colored detail. The detail is shown by the color differences. The colored pixels are all there is in a digital picture.

Pixels are real, they exist, in fact, pixels are ALL that exist in digital images. There is nothing else in a digital image. We don't need to see each pixel individually, but the image Size dimension in Pixels is the First Thing To Know about using any digital image, because this size in pixels is what is important for any use. The size of a digital image is dimensioned in pixels.

FWIW, we see some fanciful things in movies, where tremendously enlarging photo prints provides clues to solve crimes. The resolution decreases as the size increases, so it really does not work that well in that degree (enlarging film is much better than prints). Enlarging digital excessively only shows pixels.

Human eyes have rods and cones which are a similar sampling system of tiny areas. Cones are color sensitive, with red, green or blue cones. Sampling the color of tiny areas is not unlike pixels in that way. The color difference of adjacent areas is how image detail is perceived. We see a black power wire running across a blue sky because the colors are different. Color difference is the detail that we perceive (including slightest tonal shades of same color). In our digital pictures, a pixel is the smallest dot of color that can be reproduced, so we do think of more and smaller pixels as greater resolution of detail.

However, digital reproduction is a "copy" of a lens image. We should also realize that it is the camera lens that creates the image that we will reproduce digitally, and pixels are the detail of reproducing the lens image. For example, in a DX cropped sensor camera, the original is the image from the lens projected onto the 24x16 mm DX digital camera sensor. The image has this 24x16 mm size there, comparing to the size of an APS-C size film image. Then, the camera pixels merely digitally sample that lens image (very much like any scanner samples an image, meaning taking many color samples called pixels) to try to digitally reproduce (convert to numbers) the image that the lens created. A pixel is just numbers, three binary RGB numbers representing the red, green and blue components of the color of the area of that pixel. The pixels do NOT create the image, and cannot improve the lens image detail. The pixel sampling merely strives to reproduce its detail. At best, it can hopefully be a very good reproduction. A 24 megapixel DX image and a 24 megapixel FX image are NOT equal, because the FX image is simply half again larger (36x24 mm), and so does not have to be enlarged as much to show it.

Essentials to Know about Using Digital Images

Image Type and Data Size Calculator

Image Size: x pixels
Data Type:
If Printed at: pixels per inch
Image Size
Data Size
File Size
Print Size

Note that 24-bit RGB data (like JPG) is 3 bytes per pixel, regardless of image size.

This calculator tries to make the point that images involve four different sizes, used for different purposes. The numbers used to describe the actual size of the image is width x height, in pixels.

Data size is the uncompressed data, the actual data size - how large your uncompressed image data actually is - normally 3 bytes per pixel (usual RGB, for example JPG files). Compressed File Size in bytes is the least useful number, only of interest for internet transfer or memory card capacity. But pixels is the important number which determines how an image can be used.

Raw files cannot be printed directly. When in editor memory, Raw is converted to 16 bit RGB, and processed, and then typically output as 8 bit RGB for viewing or printing. JPG is always 8 bits per RGB channel, or 24 bit color.

The compressed file size will be smaller (JPG will be much smaller, variable with JPG Quality setting, but file perhaps only 10% or 20% of data size).

Exif data may be added, and a few formatting bytes. Indexed files add a small RGB color table, for each color. Not added into the size here, but Camera Raw image files also contain the cameras Large JPG image too (this JPG is shown on the camera rear LCD, and it provides the histogram too). Simple photo editors (not raw editors) may show this included JPG as being the Raw image.

Regarding color bit depth, our monitors and printers are 8-bit devices. Many inexpensive LCD monitors have used only 6 bits (18-bit color). For photo work, look for the better monitors that actually specify 24-bit color. Good IPS monitors are becoming inexpensive now (I've been really pleased with a low priced Dell IPS monitor).

Desired Image Size Goal

To print   x  

at dpi resolution  

This little calculator will serve two purposes:

  1. It will show the output image size created (pixels) if the area is scanned at the dpi resolution.
    Scanning 8x10 inches at 300 dpi will produce 3000x2400 pixels.
  2. It will show the required image size (pixels) to print this paper size at the dpi resolution.
    3000x2400 pixels printed at 300 dpi will print 8x10 inches on paper.
  3. It's important to realize that an area scanned at 300 dpi will create the pixels necessary to also print the same size at 300 dpi. The concept either way is pixels per inch. 300 dpi is likely what you want for a photo copy job (a line art scan of black text or line drawings can use 600 dpi well).

This dpi number does NOT need to be exact at all, but planning size to have sufficient pixels to be somewhere near this size ballpark (of 250 to 300 pixels per inch) is a very good thing for printing.

Copyright © 2012-2018 by Wayne Fulton - All rights are reserved.

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