File Sizes

For every 1024 bytes, that makes one kilobyte. For simplicity we are going to round to 1000 so that we can do the math in our heads.

Each unit changes names when you get to 1000 of that unit. The basic unit is a byte. If you have 1000 bytes, you can then call it 1 kilobyte. If you have 1000 kilobytes, you can then call it 1 megabyte. The same happens when you go up from megabytes to gigabytes.

Each chart below shows equivalent amounts. Note that the decimal place moves three places either to the right or left.

 

Rebellion by Arcard Fire -  5:10 length -  4,841 KB (4.8MB)

Photo of Pimrapee - 4.8 in x 7.2 in @ 72 ppi - 8 bit RGB JPEG - 171 KB

 

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Bit Depth (pixel depth) 

Colorspace

 

 

Bit is short for binary digit, the smallest unit of information in the digital world. A single bit can hold only one of two values: 0 or 1. (On or Off) A bit-mapped image is made up of dots. A dot is a single point, the smallest identifiable part of an image. Image files are often described by the number of bits used to represent each dot or pixel.

Bit depth -- also called pixel depth or color depth -- measures how much color information is available to display or print each pixel in an image. Greater bit depth (more bits of information per pixel) means more available colors and more accurate color representation in the digital image.

A 1-bit image is monochrome, each dot is either on or off; hence the image is only rendered in black and white, with no shades of gray.

An actual 8-bit image supports 256 grayscales or 256 colors (think very, very old monitors, old graphics apps and web-safe colors) This would be a black and white image with 256 shades of gray. This could also be an indexed color image with only 256 colors, like the GIF format.

We often call an RGB image 8-bit. Actually it is 8-bits per color channel (8x3). This is also referred to as a 24-bit image. In this image each dot or pixel is represented by 24 bits. Using 24 bits means that more than 16 million unique colors can be represented. Since humans can only distinguish a few million colors, this is more than enough to accurately represent a color image.

A 16-bit per channel image actually has 48 bits (16x3) of color information in each pixel. A 48 bit image is capable of billions of colors. This can be valuable when your are editing in Photoshop if you begin with a high bit depth file.

source: www.alouwebdesign.ca/toolkit/file_sizes.htmr

 

 

4.8 inches x 7.2 inches @ 72 ppi - 8 bit RGB JPEG  |  4.8 inches x 7.2 inches @ 72 ppi - 1 bit  JPEG

8bits - 2 x 2 x 2 x 2 x 2 x 2 x 2 x 2 = 256 colors or tones 

An 8 bit RGB image is also known as a 24 bit image (above) has 8 bits per Red, Green & Blue Channel, or 24 total bits - 16.7M colors.

6 Bits - 2 x 2 x 2 x 2 x 2 x 2 = 64 colors or tones

3 Bits - 2 x 2 x 2 = 8 colors or tones

1 Bit - 2 x1 = 2 tones (black and white) Above, right

 

Bit Depth. This is sometimes called ‘Pixel Depth’ or ‘Colour Depth’. A pixel with a ‘bit depth’ of 1 has two possible values: black or white. A pixel with a ‘bit depth’ of 8 has 28, or 256 possible values. A pixel with a bit depth of 24 has 224, or approx. 16 million possible values. The greater the ‘bit depth’ the finer the levels of change that can be recorded so the higher fidelity the gradations of the image. Naturally the equipment to perform this task this is more expensive and the resulting file size is correspondingly larger. As a consequence more space is needed in the computer system to handle and store the image. Depending upon scanning options, bit depth can be 24, 30, 36, 48 or even 64

Calculating File Size: Simple calculation. Multiply the total number of pixels by the number of 'bits' of colour (usually 24) and divide the result by 8 (because there are 8 'bits' in a 'byte'). e.g. An image containing 1200 x 800 pxls 1200 x 800 = 960,000 = 960,000 pxls x 24 (usual ‘24 bit depth’ for a digital camera) = 23,040,000 ÷ 8 = 2,880,000 or as we say 2.88mb The above formula will provide a quick reference to estimating file size (and therefore a guide to resolution). Note: the file format used to save the image information can change the figure calculated but not by a vast amount. Files can of course be 'compressed'. So it's the 'expanded' or uncompressed file size that's really important. source: www.crhfoto.co.uk/crh/bitandfile.htmr

 

Toledo Blade Photo