Week 6

Digital Photography

File Formats October 14, 2005

Memory

 Camera Memory  There are several types, typically flash memory  How much do you need?

 Depends on sizes of images, resolution and file format  Archiving  Backups to cds/dvds  DVD capacity usually = 2.4 GB  CD capacity = 700 MB Week 6

Resolution = Information

   Higher resolution = more image information   The more pixels we have in the image, the larger that image can be reproduced The higher the density of pixels in an image, the more detail or quality the image will exhibitM Pixel count (number of megapixels captured by camera)  More pixels means that images can be reproduced at larger size (and still look good) Pixel density (number of dots per inch for a print = number of pixels

in a given area

)  Higher density of pixels means more detail or quality in the image Week 6

MegaPixels

    1 MegaPixel – 3MB file size  4X3’’ photo 2 MegaPixel – 6MB file size  5X3.5’’ photo 3 MegaPixel – 9MB file size  6X4’’ photo 6 MegaPixel – 18MB file size  10X6’’ photo Week 6

File Formats

    Lots of Image file formats    JPEG TIFF RAW   GIF (often on web pages) PSD (Photoshop format) Why are there different formats? What exactly do these formats do?

When should I use what?

 The camera generally stores JPEG images Week 6

File Formats

    Jpeg (most cameras)     Lossy compression Smaller file sizes Different image sizes (may be offered on computer) Different options for amount of compression TIFF  No loss RAW  Camera format, but must convert when working on them  Most flexible, best if offered PSD  Photoshop files Week 6

File Formats Are Different

   They store information differently Can’t change a file format by going to Window’s Explorer and changing extension  Must resave or export the file to change the format Different file formats are better suited to different tasks  And in some cases, it doesn’t really matter Week 6

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JPEG

Joint Photographic Experts Group (JPEG) is technically a file compression algorithm rather than a file format. The actual file format is JFIF (JPEG File Interchange Format), although JPEG is more commonly used.

JPEG is the most common file format for digital cameras because of the outstanding file size reduction capabilities.

JPEG compression uses a sophisticated mathematical technique called a discrete cosine transformation to produce a sliding scale of graphics compression.

 Choose degree of compression (also determines image’s quality)  Algorithm discards "unnecessary" data as it compresses the image, and it is thus called a "lossy" compression technique.

Save your original uncompressed images!

 Once an image is compressed using JPEG compression, data is lost and you cannot recover it from that image file. Always save an uncompressed original file of your graphics or photographs as backup.

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Jpeg Example

   Original Image  1126 KB Original Image saved with quality 0  347 KB 2 nd image (quality 0) saved with quality 12  1809 KB  Notice “crispness” at 200% of original image is lost in 2 nd and 3 rd images (even though 3 rd image is “bigger” than original) Week 6

Saving with high compression

 Always setting quality to 12 will just increase the file size, and does nothing to image quality  See the files at:  reSavingSameImageWithLevel12Compression  OriginalImage: 1126 KB  Same image, saved 10 times with level 12 compression each time: 3095 KB Week 6

Different Quality Levels

     Original – 1126 KB Quality 0 – 327 KB 1 – 397 KB 2 – 542 KB 3 – 589 KB 4 – 682 KB     7 – 1069 KB 8 – 1247 KB 9 – 1452 KB 10 – 1639 KB   11 – 1982 KB   Week 6 5 – 852 KB  12 - 2846 KB 6 – 1030 KB

But original image can’t be improved after we’ve taken the picture!

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Resaving JPEG Images

Because JPEG is a lossy compression scheme,

files should be saved in the format only once (if at all)

 Resaving a JPEG file in JPEG format sends the image through the compression process again, possibly resulting in damage to the image's appearance because of the second round of data loss.

With the booming popularity of digital cameras, more and more images are being captured as JPEGs.  To best understand how to avoid damaging an image when resaving it as a JPEG, you should know a little about how JPEG compresses.

 Degree of compression matters for image’s quality  Different programs use differing JPEG quality/compression scales. Photoshop uses a 13-step scale (0–12), Illustrator uses 0–10, and Save for Web works with 0%–100% Week 6

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GIF

GIF is a common Web file format, suitable for illustrations and other images with large areas of solid color and no or few gradients or blends.

 This file format is not appropriate for most photographs and other continuous-tone images because it can record a maximum of only 256 distinct colors. GIF files incorporate a compression scheme to keep file sizes at a minimum, and they are limited to 8-bit (256 or fewer colors) color palettes. Several slight variants of the basic GIF format add support for transparent color and for the interlaced GIF graphics popularized by Netscape Navigator.

Uses a relatively basic form of file compression (Lempel Zev Welch, or LZW) that squeezes out inefficiencies in the data storage without losing data or distorting the image. The LZW compression scheme is best at compressing images with large fields of homogeneous color. It is less efficient at compressing complicated pictures with many colors and complex textures.

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Week 6 http://www.webstyleguide.com/graphics/jpegs.html

LZW Compression

  Lossless compression scheme, meaning that although the file gets a little smaller, no information is lost. Take this string of digits:    

14745296533333659762888888356789

Is there a way to store this that doesn't lose any digits, but takes less space? The answer is yes. One way would be as follows

1474529653[5]6597628[6]356789

Here the string 33333 has been replaced by 3[5] - meaning a string of 5 3s, and the string 888888 has been replaced by 8[6] - meaning a string of 6 8s. You've stored the same exact data, but the "compressed" version takes up less space. This is similar (but not identical) to the way lossless TIFF compression is done.

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GIF and LZW compression

TIFF

    The Tagged Image File Format (TIFF) is a

very flexible

image format which was created by Aldus Corporation to save images created by scanners and image manipulating programs. It usually uses an 8 to 16-bit per color channel storage method without losing image data. A disadvantage is that it creates very large files. Typically an image from a 5-megapixel camera will take up more than 14Mb of space on your storage card.

There are variations to how TIFF compresses files. Some use the LWZ (Lempel-Ziv-Welch) algorithm (approx 1/3 of original size) Week 6

Nikon 5400: Tiff vs Jpeg

   Same picture & same settings Tiff image    HI image quality – saves as tiff Slow to save to memory card Takes up 14874 KB Jpeg image    Fine quality (or lower) automatically saves as jpeg Faster to save to card Takes up 1853 KB Week 6

Tiff with Compression

 Take the 14874 KB image from the camera  Save the file with LZW file compression in Photoshop (no information is lost)    File is now 5204 KB 1/3 the size of the original image!

But we can’t do compression on the camera, which is where our storage is probably most limited!

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RAW

A

RAW

file is sometimes referred to as a true digital negative. The ability to shoot RAW is found on most advanced and professional digital cameras. With a RAW image file, no processing is done by the camera (such as sharpening or white balance). This gives total control to the photographer when he or she post-processes (edits) an image.

The

RAW

by every image editor. It can take longer to process on your computer. format is not used widely and it can not be opened Since there is no accepted standard format for RAW files, each manufacturers format is different. (Nikon has its own RAW format on higher-end cameras) Week 6

Photoshop - PSD

  PSD is the native bitmap file format of the Adobe Photoshop graphical editing application. Supports all the program's capabilities.   Most workflows benefit from maintaining a file in Photoshop format until it's time to create a final TIFF, EPS, JPEG, or other file. It's also usually a good idea to maintain the original image, with editable type and layers, for future use.

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Good Habits

  Do not leave camera images as JPEGs as you start to manipulate them  Manipulating them means ANY changes where you have to re-save the image (rotating, cropping, etc) Save backup images in a loss-less image format  For digital photos: TIFF or PSD is best  Use TIFF when you aren’t working with Photoshop  Use PSD when you are working with Photoshop Week 6

Photoshop: Save for Web

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Jpeg, 30 KB GIF, 54 KB

Let’s you save files in smaller sizes, with options for different formats, colors, etc

Save For Web Options

  Typically you want smaller file sizes, 20-60KB with resolution at 72 pixels/inch    In previous example, I made the pictures about 15% of the original size as well as lowering resolution Jpeg compression was set to “medium” Gif format used 32 colors in the image Progressive JPEG will allow a lower-resolution file to appear first on screen, and then quality improves as file downloads Week 6

Photoshop: Web Gallery

 Automate > Web Photo Gallery  Allows you to easily make a web page of a folder of pictures  Preset styles to choose from  Source/Destination folders  Options drop-down menu - lets you control image size, banner, colors, etc Week 6

Next Week

 No homework this weekend but if you want to take pictures, try to focus on capturing color  Next week we will learn about color theory and how to effectively use color in photographs  Test  Would you prefer the test on Thursday or Friday?

Week 6