Digital Files

• Digital Files• File Format• Storage• Color Temperature

PIXELS

• Pixel = picture element- smallest component of a digital image

- MEGAPIXEL

1 million pixels = MEGAPIXEL

PIXELS

— more pixels per inch = sharper image andhigher resolution

— pixels are the equivalent of film grain in adigital image. They are the smallest unit ofinformation in a bit-mapped image.

PIXELS

Penelope Umbrico Unititled (pets and babies) from home decor websites

Penelope Umbrico 87 Suns from Flickr - 29 Visible

Penelope Umbrico

Thomas Ruff

BIT–Binary Digit

• the smallest unit into which the camera (orany computer) is able to digitally dividevisual information.

• the number of distinct colors that can berepresented by a pixel depends on thenumber of bits per pixel (bpp)

• More BPP = more nuance in color andbrightness or density

Bit Depth

• The number of bits used torepresent each pixel in an imagedetermining color and tonal range.

• Greater Bit Depth means greatervariety in color and tone.

PIXELS AND BIT DEPTH

UNDERSTANDING BIT DEPTH

better imagesmore control

Digital images are usually made up of one, threeor four channels

– RGB has three channels (red, green, blue)

– CMYK has four (cyan, magenta, yellow,black)

– K (grayscale image) has one (black)

• Typical images are 8-bit or 16-bit inimaging software such as Photoshop.

• In an RGB file, an 8 bit/channel imagehas an overall bit depth of 24 bits, 16bits/channel = 48 bits (8 bits x 3 channels= 24 bits) *

• 8 bit images are 256 colors per channel(28) and offer (256 x 256 x 256)= 16.7million colors

• 16 bit images are 32,000 colors (216) perchannel

Digital Camera Resolution - INPUT

• PPI• pixels per inch – this describes the

digital, pixel resolution of an image.The pixel resolution is the number ofpixels per inch in the input digitalimage.

Printer Resolution - OUTPUT

• DPI - dots per square inch

Camera Resolution

• Maximum number of pixels (PPI) the camera iscapable of capturing (e.g. 6-megapixelcamera)

• A megapixel is one million pixels so a 6-megapixel camera is capable of 2000x3000 ppiimage.

• For a maximum print size divide by 300• Megapixel calculator:

http://web.forret.com/tools/megapixel.asp

Image Resolution

Image resolution is medium specific• Screen (72 ppi)• Inkjet Print (240-360 dpi) (Note: The

human eye is not capable ofdiscerning pixels in a print which ismore than 300dpi)

Camera File Format

JPEG:Joint Photographic Experts Group

- LOSSY compressionformat

- In-camera settings:Basic, Normal, & Fine

- Allows more imagesper megabytes ofmemory

Camera File Format - LOSSLESS

TIFF: “Tag Image File Format”- No compression- Standard in graphics and printing fieldsRAW: Unprocessed sensor data- Pure Digital Negative- Format can vary between camera manufacturers- most common: DNG / NEF / CR2- The settings used to take RAW images are saved, but

they are not permanently applied to your images untilyou save them in another format such as JPEG or TIFF.

• If you shoot using RAW, white balance is not ascritical as when shooting JPEG because youcan decide the most appropriate whitebalance when you process the file later.

• If you shoot using JPEG, the camera is decidingautomatically at the time of shooting how to setthe white balance and tonal corrections, oftenclipping the highlights and shadow detail.

Zoom level Workflow options

HistogramFull ScreenTool Bar

Open in Photoshop

crop

straighten

retouch

Red eye tool

Camera raw preferences

Rotate tools

Camera

Raw

icons

zoom

hand

White Balance

Color sampler

File size: measured in bytes, kilobytes, megabytes,

gigabytes

• File size is how much storage memory your file occupies on yourdisk and depends entirely upon how much information is in yourimage.

• File size is often confused with image size, which is the physicaldimension of our image (see next slide)

The image size of the imagebelow is 4x5 inches or360x288 pixels. If youdescribe an image with itspixel height and width, youare referring to its pixeldimensions

• File size affects:- the quality of the image- the space the image takes up on your

drive- big files can’t be easily sent over the

internet- time

Image Size

• the physical dimensions of your image,measured in inches, pixels, etc

• in order to find out how many pixelscomprise your image, multiply eachlength by the ppi

• for example, an image that is 8”x 10” at300 ppi is comprised of 2400 pixels by3000 pixels

How big can you print an image?

• Divide the number of pixels along both dimensionsof the picture by the pixel resolution you wish to print

• How big can you print an image that is 4800 x 6000pixels at 300 dpi?

Interpolation (Resampling)the act of increasing the number of pixels based on the

original pixel information and is generally used when tryingto make large print from a high quality, but relatively small

image.

Photoshop offers 5 Interpolation methods. Whensampling up, it’s best to use Bicubic Smoother,

while Bicubic Sharper is best for sampling down.

Deselect Resample Image to avoid resizing with Interpolation

Memory Cards, Card Readers and External storagedevices

• insert and remove memory cards when thecamera is off

• Remember to eject (move to the TRASH) allexternal devices including storage and cardreaders.

• Eject card reader before removing memorycard

• Upload images using a card reader rather thanthrough the camera

BACK UP YOUR IMAGE DATA!!!

• Nothing is failsafe• The best insurance is to back your

files up in several places -- harddrives, flash drives, cds, dvds

Color - RGB

Sergei Prokudin-Gorskii The Emir of Bukhara, 1911

Sergei Prokudin-Gorskii Self-Portrait, 1912

Florian Maier Aichen Untitled, 2011

Color TemperatureThe colors reflected from a subject areaffected by the color of the light sourceilluminating it.

The color ofthe light isspecified by itscolortemperature indegrees Kelvin.

The color oflight changesduring differenttimes of the dayand at differenttime of the year.

Color Temperature

Photographic Color Wheel

Eachcolorabsorbsitscomplementarycolor.

Color CastsA trace of color in all the colors in an image.

Neutral color preserves thecolor of the subjects/objects in theimage most accurately to their truecolor with less or no color cast.

Your camera’s white balance systemremoves color casts that wouldotherwise be created by the color ofthe light source.

It’s purpose is to capture images withcolor that look like they were shot atmidday.

Auto White Balance

Custom

Flash

Fluorescent

Incandescent/tungstenCloudy

OpenShade

Direct Sun

White Balance Camera Settings