Message-Id: <mailto:199507252343.SAA23574@library.wustl.edu> Date: Tue, 25 Jul 1995 18:47:50 -0400 From: "mailto:Walter_Gilbert@UMAIL.UMD.EDU--Maryland" <WALT@UMDD.bitnet> Subject: Re: Advice requested for scanning to PhotoCD To: Multiple recipients of list IMAGELIB
On Tue, 25 Jul 1995 10:52:37 -0500 Mia Massicotte said: **Reply from Walter Gilbert, University of Maryland at College Park >I need some advice, and I hope that I'm directing these questions to the
>appropriate place.
>
>...shots of our library for a virtual tour...
>...images on a PhotoCD...manipulate on a Mac with Photoshop...
>...mount on Mac webserver. I would like one high
>quality archival image for posterity, one image at 72 dpi for the
>webserver and subsequent screen viewing, and one thumbnail.
>
First of all, Mia, 72 dpi doesn't mean anything when dealing with slides and Photo-CD. It's more useful to think of image size in terms of pixels, e.g., 512x768 pixels.>My questions are:
>
>1a. For the image at 72 dpi, I don't want to have to resize or crop these
>images when I place them into my web pages.
If you don't resize or crop, the Photo-CD gives you 5 sizes to choose from: immense (about 2000x3000 pixels); huge (about 1000x2000 pixels); the base image (as they call it): 512x768 pixels; the "wallet size": 256x384 pixels; and the thumbnail: 128x192 pixels. In reality, under these constraints, you will have three sizes to choose from: base, wallet, and thumbnail.
>...want the images approx 4" h x 5 inches wide when displayed on a monitor.
The size of the image is something that you will have no control over. It depends ENTIRELY on the monitor and video "card" of the viewing computer. In my experience, most "older" Macs can't really display an entire base image, 512x768 pixels on the screen, the same for "older" PCs. Newer equipment can do better. If you want to accommodate everyone, you are probably stuck using the 256x384-pixel wallet image; if you want to reward those with good equipment, use the base image. You can even do both: give the viewer a choice.
>the 'aspect ratio' should be 4x5 for 35 mm film.
The aspect ratio for 35mm film is 2:3. There's no "should be" about it: that's what God has decreed. Therefore, you Photo-CD images will have that aspect ratio (the ratio of the size of the short side to the long side). Notice that all of the pixel sizes I have mentioned (e.g. 512x768) are in this ratio.
>This should result in an on-screen image of
>300 w by 200 h pixels. Is my information correct?
>
Again, Mia, the on-screen image size (in pixels, not inches) will be determined by which size you select from the Photo-CD. By the way, if you are doing no editing, cropping, or resizing of the images, PhotoShop is very much overkill for this purpose. Kodak's "Access" package is designed for the purpose of getting images from a Photo-CD in the size and color depth (to be defined) you want with little fuss or muss.>1b. If I want the 72 dpi images instead to display on screen (without
>cropping) at a size of say, 3" high by 4" wide, how should I specify this
>to the lab making the CD?
>
Again, Mia, the size on the screen in inches will be determined by the capabilities of the computer viewing the images. For example, I have a fairly high resolution monitor and video card (on a Windows system): my screen is 1280 pixels wide and 1024 pixels high; in inches it is about 11.25"x9.5". Therefore, when I display a 512x768 pixel image, it occupies one quarter of my screen, either 5.6"x4.8" or 4.8x5.6, depending on its orientation. Someone with a 14" monitor capable of 800x600 pixels could barely fit it on the screen with the borders, etc., that Netscape adds. Therefore, there is nothing you can tell the lab making the Photo-CD.>2. For the 72 dpi image, I assume that the image would be in PICT format
>on the CD.
Actually, on the CD they are in a proprietary Kodak format which is definitely not PICT. They call it PCD (for Photo-CD, of course) but it is also sometimes call YCC or something like that. The bottom line is that you don't care what the format is, the software you use to copy it from the CD will put it into the image format of your choice.
>If I then convert the 72 dpi image to jpeg for my web project,
>will this result in too great a loss of quality? Should I try to convert
>the archival image to a 72 dpi jpeg instead? Any suggestions?
>
Again, 72 dpi only has meaning if you are putting paper on a scanner and scanning at 72 dots/pixels per inch. There is no such thing as 72 dpi JPEG. Now we are in the very complex issue of image format. For the Web, you have two defacto standard image formats: JPEG and GIF. JPEG is a complex but very, very useful format which can be used to compress images to just about any level of quality you desire. GIF is a proprietary (CompuServ) format which is lossless (what you put in you exactly get out). However, GIF can only accommodate 8-bit color depth (or less) while JPEG is good at 24-bit color. (Oh, dear, if you're really interested in color depth, call me--phone number below.) The "right" way to use JPEG is to, one by one, compress your images at a certain "quality level", then decompress them and see if the quality is OK, if not, recompress at a higher quality level.>3. Initially, I used Apple's QuickTake digital camera for some quick and
>dirty prototyping. I noticed that displaying the photos (I had converted
>from pict to gif for the test) on Mac monitors (475's, 575's, Powermacs)
>looked acceptable; but on PC monitors were way too dark. Is this darkness
>a function of the PC monitor's capability, or did it have more to do with
>the gif compression? Will I run into a similar problem with my jpeg
>images, and if so, can it be avoided?
>
The difference is in the monitor adjustments, not whether they are Macs or PCs or Unices. If my monitor is not properly adjusted, all of the images I see will look wrong. There's nothing you can do about that. The television people have the same problem: some people see Jay Leno in purples and greens.>The bottom line is that I want the highest quality image that I can get
>from the original, to mount on my Mac webserver, for monitor display at 72
>dpi, with an on-screen size of about 300 pixels wide by 200 pixels high.
By saying about 300x200 pixels, you have defined the image resolution: it's fixed by its size.
By the way, the Photo-CD is a comparatively good archival medium for your images. (In fact, the current CD technology will be totally obsolete long before your images deteriorate on the disc.) The 2000x3000 (poster-size) image on the CD is very good: better than you will probably ever need.
If your photographer hasn't already had the film processed, it is much, much better and much, much cheaper to have the CD made at the same time the film is processed (assuming he/she didn't bracket too much). Walt >Mia Massicotte, Systems Librarian
>Concordia University Library, Montreal, Quebec CANADA
mailto:>mailto:miamass@vax2.concordia.caWalter Gilbert, Asst. Dir. mailto:Walter_Gilbert@umail.umd.edu Computer Science Center Manager: Teaching Technologies University of Maryland at College Park 20742-2411 (301)405-6727