Imaging

1. Imaging File Types and Sizes Scanning and Photography

2. Introduction • This presentation is designed to explain what the various file types are for imaging, how to determine which to use, and how to determine what resolution to use and the sizes of files to be generated when producing digital images.

3. Scope of the presentation • This presentation has been confined to the strictly essential elements of DOMESTIC usage. • Although the topics of producing pictures using a camera, and the use of scanners to record an image are mentioned, this presentation is not intended to be a guide to either process – but merely to provide essential information about the handling of the image information …….information that is not readily available elsewhere, but is vital to enable the above-mentioned topics to be accomplished correctly.

4. Like me, I’m sure that you have all generated image files of one sort or another – but I found that I didn’t really understand the subject fully, and therefore kept deferring the job of transferring my collection of prints and slides to digital form.

5. I went through a series of five digital cameras before I got one that was adequate, and subsequently replaced that with one to do the job properly!When I eventually began the long process of transferring my non-digital images into digital form, I got half way through the process before finding that I had done most of it incorrectly – just because of insufficient information.

6. For simplicity – to keep this presentation short – everything has been described in terms of using the 35 mm format and ‘simple’ digital cameras, and some aspects have been a little generalised and are not wholly accurate in absolute terms.

7. There are three situations to be considered:-1. Using a camera to produce digital images.2. Transferring conventional slides and negatives to digital form,3. Transferring prints into digital form.

8. Prints or Slides? – 1. • Although in the past, most users have made use of conventionally printed photographs rather than slides, this is changing …slowly. • However, many digital users still persist in obtaining prints just as they always used to from their ‘happy snaps’ machines. Often, the digital images are not retained. • For those that have home computers, better options are available, but the ‘print’ mentality largely persists. This presentation is directed towards persons that will use home computers to process images!

9. Prints or Slides? –2. • Once camera-produced images have been transferred to either CD-ROM or hard disk, then effectively the images are in ‘slide’ form, but the way in which the images have been saved may limit what can be done with them. • To enable those images to be suitable for use subsequently, the user needs to understand something about storage formats, and the requirements necessary for later processes.

10. Planning the Storage – 1. • Like many processes, it is necessary to look at the final results required, then work backwards to determine how the image should be captured. • Final requirements could be images for:- Internet usage Screen views Printing (domestic) Projection as slides, or most other purposes.

11. Planning the Storage – 2. • Images intended just for use on the internet, have the least critical requirements. • Images intended for use as slides – or commercial printing, etc. have the most demanding requirements. • Never lose sight of the fact that a good original slide or negative on conventional film will be better (when originally produced) than any digital version – but film can deteriorate.

12. Ultimate Image Sizes - 1. • Whilst most users that are looking for prints will not generally wish to exceed 5”x7” in size, the negatives or slides used to produce these are capable of producing much larger prints – with 8”x10” and even 16”x20” (approx A4 & A3) available using home processes, and 24”x36” prints are readily available at modest prices from high street processors. • Slides are generally projected at home onto screens of up to 60”x60” in size.

13. Ultimate Image Sizes – 2. • With digital images, most (excepting Internet ‘thumbnail’ images) will be capable of producing small-sized prints, but will not be usable for producing larger prints unless the digital image is of an appropriate size and type. • Most images will be viewed initially on-screen, where the image-size is much less demanding than that required for printing. • You will learn shortly about ‘pixels’ and ‘dots-per-inch’ (dpi) in terms of resolution and image sizes.

14. Ultimate Image Sizes – 3. • ALL images are composed of a series of dots; on paper, these are ‘dots’ of ink; on screens these are ‘dots’ of light – and are referred to as ‘pixels’. • However an image has been stored, when it is converted into ‘dot’ form there is a maximum size that the image can be shown, and this is where the generation of ‘dots’ has reached the limit of one ‘dot’ per piece of image information. • Once the practical limit of enlargement is reached, the image will become ‘fuzzy’ and deteriorate into a series of rectangular ‘blotches’ as magnification increases.

15. Images from digital cameras -1 • This is the easiest of the three topics to handle. Most of you here will already own a digital camera of sorts, so you will be stuck with the inadequacies of it. There are currently only two 35mm cameras on the market that produce results of professional quality. • Unless you are prepared to settle always for small sized prints, set your camera to produce its’ best possible file type (explained later) and largest possible file size; the reasons for this will become apparent subsequently.

16. Images from digital cameras–2 • Simple cameras produce only JPG format output; this is NOT the best format to use – because it is a ‘lossy’ compression format, which is to say that each time the file is opened and saved – it is re-compressed and looses quality with each recompression. (Merely opening to view or print, or simply copying an unopened file does not change the data). • The file sizes produced in camera generally limit the possible sizes of prints substantially. • Never lose sight of the fact that ‘JPG’ was designed for Internet usage because it’s fantastic compression characteristics speeded-up downloads. It is not suitable for ‘master’ images.

17. Images from digital cameras–3 • Some cameras offer to produce files in TIFF format, but rarely define this; TIFF files may be so variable in format, that this includes an option that is actually no better than JPEG; to be any use, TIFF files must be either uncompressed or use lossless LZW compression, and be 48-bit. • RAW files are the best, as these contain ALL of the image data produced by the camera.

18. Images from Digital Cameras - 4 • JPEG files from simple cameras can vary in size from about 1 MB up to say 2.5+ MB. • More sophisticated cameras may produce JPEG files of up to 12 MB or more. • ‘RAW’ files often begin at about 5 MB, and currently go up to 22 MB. • TIFF files generated in a computer from a 14 MB RAW file, will be about 50 MB.

19. Images from Slide Scanners– 1. • Slide Scanners normally handle both Slides (transparencies) and negatives, and cost from about £100 upwards. • If possible, always choose to scan the original film frame, rather than a print made from that frame, as the result is likely to be better.

20. Images from Slide Scanners – 2. • Try to obtain a slide scanner that has an optical resolution of at least 2700 dpi; better machines go up to 4000 dpi. These numbers apply to the scan output – input scan may be higher. • In general, Scan in at maximum OPTICAL resolution – that may be higher than the nominal output resolution – and save at the highest output resolution. Aim to produce an IMAGE in computer memory of between 25 and 30 MEGA BYTES (before compression) for colour, or about one third of this for greytones.

21. Images from Slide Scanners- 3. • Be aware that some scanners will appear to offer resolutions far in excess of their capabilities (the OPTICAL resolution), and may try to produce images and files of sizes beyond the capabilities of your computer. Use previously recommended OPTICAL sizes. • You may have to experiment to determine what size of uncompressed file your scanner produces for a given resolution (dpi value).

22. Images from Slide Scanners- 4. • If any slide cropping is necessary e.g. to remove ragged mount edges, do it after the preview stage and prior to the final scan so as to save the required part of the slide in greatest detail. • Any exposure or colour correction necessary is best done prior to saving the scanned image, if the format for saving will be a ‘lossy; compression such as JPG.

23. Images from Print Scanning- 1. • You can either scan these to the same size as the original, or effect a degree of enlargement by using a higher resolution. However, using higher resolution will not increase the amount of detail visible, and may not improve small prints made on very basic cameras. It’s often hard to tell at what so-called resolution the device is actually scanning • Some software will enable you to scan larger pictures (or documents) in sections that the programme will subsequently join together – so you could for example create an image from an A3 print even though the scanner has an A4 platen.

24. Images from Print Scanners- 2. • Some software allows the operator to set an output file size, and varies the “dpi” to produce this from different sizes of originals, whilst with other software the operator has to adjust the resolution manually and determine by trial and error what the image size will be. • Because the user already has the print, there is a presumption of a wish to ‘improve’ upon it, so normally one would aim to generate images of the same sizes as determined for slides (where possible), but the intended usage will determine the most appropriate size.

25. Image Sizes for production of Prints. • So far we have considered producing images with the ‘greatest possible’ detail – within the limitations of domestic equipment. Once produced, the image can still be used for less demanding purposes, but if insufficient detail has been captured initially, there may be no opportunity to rectify the position later.

26. File sizes for printing • Much storage space could be saved on your computer, and more images might be squeezed onto the capture card in your camera, if you determine that you require prints of a certain maximum size – and not anything more. • Most ink-jet printers have a maximum resolution of 300 lines per inch (lpi). You can work with that number if you wish, but better print quality will be obtained by using double that number. Lower resolution may be used if desired down to 150 lpi,

27. File sizes for screen viewing • For just viewing on screen, typical screen resolution is 72 dpi, but a better number to use is 96 dpi – so even more space can be saved if only screen viewing were required. • Thumbnail images require only miniscule amounts of storage space!

28. Quality Printing • To produce a good quality print in A4 size, an image size in computer memory of around 25 to 30 Mega pixels is required. • The variation in size occurs, because of the variation in ‘cropping’ that occurs when an image does not exactly fill the scanned area, and also because a degree of compression occurs with large areas all of the same colour without variation. • Should you wish to consider the next size – A3 – you will need to quadruple the image size (and therefore resultant file size), and this is generally beyond the needs and capabilities of domestic users – except perhaps for selected pictures.

29. File Types • There are about ten different file types to consider using - domestically. • These are RAW, JPG/JPEG, JPG 2000, TIF/TIFF, XIF, PSD, PCD, PDF, GIF and PNG. • By far the most common usage, is the JPG format – but it is certainly not the “best”; however, much will depend upon the user’s requirements. • Camera users will often have only the JPG option available (maybe in different “qualities”), but better equipment may offer TIFF and/or RAW. • Some of the other file types are available only via scanner software or image processors.

30. “RAW” • “RAW” image formats are an option available just on the better types of camera, and produce the largest files available on those cameras. • RAW images are capable of the greatest degree of manipulation – by the appropriate software – but each camera manufacturer has its’ own RAW format, so the resultant files are accessible just to those users that have the software supplied by that manufacturer – but this is usually a free download. Files can usually be saved after manipulation in one of the ‘standard’ formats such as JPG or TIFF etc. Sometimes a plug-in to Photoshop format is available, but of course not all users have Photoshop.

31. JPG or JPEG • This format was designed for Internet usage, because of the degree of compression that it gives, that is of course particularly critical when downloading files over a slow connection. • Compression of up to 97.5% of the original image size is possible – but not without loss of some detail – and any subsequent saving of the image after decompression, results in further losses. • The better software programmes offer a degree of control over the amount of compression that occurs – coded 1 (Most) to 10 (least). • JPG functionality is included in Windows, so virtually all PC users can use this format.

32. JPG 2000 • This is a relatively new format whose functionality is not included in Windows. Software plug-ins to process it are available free to download, but most sites attempt to charge for it. • It claims to offer a high degree of compression without loss, OR a greater compression with loss. Its’ lossless compression uses the same formula as WinZip etc. • Most domestic users haven’t heard of it, and won’t know how to access images in that format. • It is “dangerous” to use, because although it contains the capability to produce 48-bit uncompressed or lossless LZW compression images, the process often defaults to producing images with standard JPEG characteristics – thereby obviating the entire point of using it!

33. TIF/TIFF • TIFF is a relatively commonly used format, but is available only in certain image processing programmes. • TIFF is available either with or without compression. The compression used is lossless LZW as in WinZip, and gives around 50% saving on file sizes. • Some TIFF formats support only 24 bits per pixel, but is considered to be the best choice for commercial PRINT reproduction; there are allegedly compatibility problems due to different specifications in use.

34. PSD • This is the proprietary format for Adobe Photoshop, and has almost become the industry standard. Some scanners use this format directly, whilst other use it under other names. • Whilst it is a good format for a single user to use for all his high-quality images, there is no general commonality with other DOMESTIC users, and thumbnail images of the pictures will not display in Windows File Manager. • The Photoshop format retains all the detail required for image manipulation that was available in the original image read into Photoshop. It can also contain data held in “layers”.

35. PCD • This is a Kodak proprietary compressed format for the storage of images on CD. • The format can be read on PhotoCD players and most CD-I players, but as these may now be considered as obsolete, I’m not too sure why the format continues. • Kodak supply images from processed films on CD in this format, plus a reader programme, and plug-ins are available for Photoshop.

36. PNG and GIF • The acronyms stand for Graphics Image File and Portable Network Graphics. • GIF is really only suitable for line graphics images, rather than photographs, and PNG is intended to replace it – but handles pictures well; however, PNG is not a commonly used and available format. • PNG supports up to 48-bits per pixel, but does not support CMYK colour space – used for commercial colour printing.

37. PDF • PDF stands for Portable Document File – a proprietary format from Adobe Acrobat. • Although this will handle photographs happily, it is intended primarily as a means of storing entire documents, and these documents may include (embedded) photographs. Acrobat 7+ can store pictures in JPG2000 losslessly.

38. XIF • This is the default storage file type used by Scansoft Pagis Pro, that scans whole pages of text and images on pages, separating out the image information for storing in a higher quality form than the text, and enabling the text to be digitised. • Preferably use a different programme for scanning photographs to get a higher resolution, or save the images as JPG.

39. Depth of Colour - 1 • I have introduced the terms e.g. 36-bit and 48-bit in connection with images, without so far explaining what is meant. • These terms relate to ‘depth of colour’. An image may be stored to a standard of just 24-bit, that handles just 256 colour variations, whereas 36 & 48 bit images can handle millions of colour variations. • 24-bit images use 3 characters of storage to record the information for every screen pixel. 36 & 48 use 6 & 8 characters resp.

40. Depth of Colour - 2 • Clearly, handling images to a greater number of bits per pixel requires more storage and resources. • 48-bit facilities are not provided by all equipment and programmes. • If requiring only simple prints, you may find that 24-bit depth of colour is adequate, and your equipment may leave you no choice in the matter. • 24-bit resolution provides just “basic” colour (e.g. As from Kodak ‘Gold’ film), but 48-bit resolution is required for more subtle colour rendition.

41. CDs produced by copy shops. • Many shops now offer the self service option to produce prints directly from various types of camera memory card. • Some of these shops also offer the option to transfer the image files to a CD. • Be aware that these process only JPG files, and then only the smaller sizes, and may not cope adequately with the larger capacity cards. They either report the card as empty, or assume the default card size and therefore see only the first few files. • The machines will produce a new CD from each memory card; images cannot be added to the CD subsequently.

42. Calculating Image Sizes • For Domestic usage, assume a maximum size of A4 for prints. If you are sure that you will never require prints as large as this, then you can scale back accordingly. • A4 is 210 mm x 297 mm, or 8.75” x 11.25”, that is to say xxxxx in pixels at 2700 dpi or xxxxx at 4000 dpi,