21st-Century Image and Data Exchange Standards

Transcription

1 Course IN st-Century Image and Data Exchange Standards Peter Sheerin Dec 3, :00 PM 03:30 PM 1

2 2 Why do Formats Matter? Image quality Interoperability Capabilities/features Alpha channel/transparency masking Color calibration Cross-platform support Future support SVG 8K PNG 23K JPEG 6K (25%) GIF 14K

3 3 SVG 8K Small file size, with no quality degradation Vector-based, scales with no loss of quality PNG 23K Lossless raster image=high quality Supports alpha

4 4 JPEG 6K with 25% quality Image quality suffers, especially sharp lines No transparency Read by all Web browsers. GIF 14K Only supports 256 colors results in dithered or banded images Not good for photographs Read by all Web browsers

5 5 Cool Things you can do With Alpha-Level Transparency This 4-color PNG has a black background that is 100% transparent, and a sea-green fill that is about 60% transparent. GIF can t do this. It is only 4,024 bytes the same image made using an alpha channel is 6,091 bytes. An uncompressed TIFF version is 650K, and one compressed using LZW + differencing is still 19K Looks great in PowerPoint XP and Netscape 7, but fill and text disappear in Internet Explorer for Windows Color Spaces srgb: a precise definition for RGB that allows srgb images to be reproduced accurately on different platforms and media under varying ambient lighting conditions. from the HTML 3.2 specification.

6 6 srgb A precise definition for RGB that allows srgb images to be reproduced accurately on different platforms and media under varying ambient lighting conditions. HTML 3.2 specification, 1997 The standard color space for: The Web, since the HTML 3.2 specification Windows 98 and higher PNG, SVG, and the Digital camera image format (EXIF) Most color printers, especially HP DeskJets and DesignJets Why srgb is Needed

7 7 Format Types Raster-Only GIF, TIFF, PNG Vector-Only DWG, DXF Hybrid, with raster and vector (a.k.a. metafiles) WMF, EPS, PDF Raster Image formats Good EXIF (JPEG) PNG TIFF 6.0 TIFF/EP (EXIF) GeoTIFF Problematic GIF CALS BMP TGA PCX Non-standard TIFFs PICT RAW

8 8 Best-Practice Raster Formats EXIF 2.1 (JPEG) Main JPEG standard not very well defined in several areas; EXIF fixes that Designed for digital cameras All EXIF images are in srgb color space EXIF metadata includes copyright, GPS data, much more Specification: htm Related spec: DCF (Design rule for Camera File system) specifies the folder and file structure for memory storage, and is based on EXIF 2.1

9 9 EXIF Sample Images PNG Pronounced PING Lossless compression Supports b&w, index color, grayscale, true-color, with transparency almost all Basics supported by all current Web browsers Lacks EXIF metadata Not all Web browsers or applications support alpha properly Specification:

10 10 PNG Sample Images pngs-img.html cubes.html TIFF 6.0 Using this spec avoids interoperability problems Works well for many applications Offers multiple page support (ideal for faxes, etc.) Cons Not supported by Web standards Many apps write invalid/funky flavors All compression formats not consistently supported, so best to use uncompressed (read: huge) Specification: F6.pdf

11 11 TIFF/EP Designed to be lossless format for digital cameras Features metadata from EXIF standard Avoids compression, other optional TIFF features Specification: ents/n4378.pdf GeoTIFF TIFF 6.0 with georeferencing metadata, limits on optional TIFF features Used by mapping and GIS applications such as AutoCAD Map, ArcInfo, and others Most photo editing software, including PhotoShop, will destroy the georeferencing metadata so be careful when modifying!

12 12 Problematic Raster Formats GIF (Graphics Interchange Format) Only supports 256 colors results in dithered or banded images Not good for photographs because of this No support for color spaces or calibration Encumbered by LZW compression patent (going away) Upsides: Read by all Web browsers Supports multiple images (slide-show animation)

13 13 CALS Not a Web Standard Bi-tonal (black & white) only good for low file size, but bad for smooth text and line work; makes rasterto-vector conversion less accurate than grayscale If you use it, use only Dimensional CALS flavor, which embeds actual printed size in image BMP Not a Web Standard Windows-centric image format An uncompressed image format that results in huge files No transparency No metadata

14 14 TGA Not a Web Standard Not widely supported PCX Not a Web Standard No transparency

15 15 Vector & CAD formats SVG DXF EMF DWG DWF PDF Good Problematic CGM WMF SWF (Flash) IGES (IGuESs) PS EPS HP-GL/2 Best-Practices Vector Formats

16 16 SVG (Scalable Vector Graphics) Best Web standard for vector graphics Also supports embedded and referenced raster images Not natively supported by any Web browser (yet), but plug-in included with free Acrobat 5 viewer Specification: DXF De-facto CAD vector standard Widely used, but not completely documented Large uncompressed ASCII format Binary compressed flavor rarely supported

17 17 EMF (Enhanced Meta File) Windows-specific Updated version of WMF, with greater precision and better support for arcs Supports both raster and vector images in same file DWG De-facto standard Not completely documented Not supported directly by printing devices Can t be inserted directly in Web pages, but can be linked with i-drop technology for drag-and-drop placement

18 18 DWF (Drawing Web Format) Not a Web standard Supported primarily by Autodesk Designed for both viewing and printing Viewers not as widely deployed as Acrobat viewer Viewer now available for Mac OS X, but not other platforms PDF Not a Web standard, though very universal Free viewer, available on many platforms, including PDAs Can mix letter-size and engineering-size documents in one file Can be huge to download if high-res images are included If low-res images are included, printouts don t look very good Supports digital signatures and encryption with x.509 certificates Version 6.0 Professional supports layers

19 19 Problematic Vector Formats CGM Important to the aerospace and automotive industries A Web standard, but no browsers support it natively, and only a few (paid) plug-ins are available. There are many different flavors, complicating conversion and support in software

20 20 WMF Not a Web standard Windows-only image format Low vector resolution represents arcs and circles with line segments Unfortunately, the most advanced Windows Metafile version supported by many applications (including AutoCAD) SWF (Flash) Not a Web standard Proprietary Macromedia format Can do some really cool things Flash plug-in widely deployed (but not completely) Great for multimedia, but not ideal for CAD drawings

21 21 IGES Not a Web standard Pronounced IGuESs by some in the CAD industry Implementation varies widely, leading to translation difficulties PostScript Not a Web standard Really a programming language, not a graphics format this makes correct support difficult to achieve Few programs can import it properly

22 22 EPS (Encapsulated PostScript) Not a Web standard Basically the same as a PS file, with many of same problems, and more Many programs will only display the low-res raster preview image, and many standards exist for this thumbnail format. The main image is printed, but this usually doesn t work unless it is printed on a PostScript printer. Importing EPS into PowerPoint will display the lowres image on screen and on non-postscript printers HP-GL and HP-GL/2 Not a Web standard Can support both vector and raster (HP-RTL) Limited color palette based on just 16 or 256 pens Most programs can only generate by plotting to a specific HP printer, making it confusing to create, and limiting features in the output

23 23 Pete s Raster Standards The Sheerin Report #5: Master Raster Best Practices in Raster Image Formats and CAD: 02_1.html Contacting Me

24 Day Job Peter K. Sheerin Product Review Editor, Game Developer magazine Editor, Gamasutra.com This address accepts only S/MIME messages those using x.509 certificates for encryption and/or signing. Published by CMP Media, former owner of a certain CAD magazine Personal Web Site Peter K. Sheerin PetesGuide.com A blog and reference site about technology mostly Web standards, but other stuff, too. pete@petesguide.com This address accepts only S/MIME messages those using x.509 certificates for encryption and/or signing. peter@petesguide.com if you can t use secure 24

25 25 The CAD Society Joe Greco President Peter K. Sheerin Secretary/Webmaster