If this is your first visit, be sure to check out the FAQ by clicking the link above. You may have to register before you can post: click the register link above to proceed. To start viewing messages, select the forum that you want to visit from the selection below. |
|
|
Thread Tools | Display Modes |
#1
|
|||
|
|||
Understanding a 35mm negative/slide scanner spec
jim wrote:
Please can someone help me understand the basics of a current advert. Ignoring all questions about quality, software, aliasing, etc etc, it is the very basic arithmetic that doesn't seem to add up. ------------ http://www.aldi.co.uk/uk/html/offers/2827_11713.htm Turns negatives into digital photos/files. Enhance or edit your favourite pictures. 5 mega pixels Film and slide strip scanner 48 bits 3600dpi optical resolution --------------------- BUT how do you connect the numbers together? 35mm negs are 36x24mm or 1.417322835ins x 0.94488189ins - at 3600 dpi that is 17.35million dots overall. Even if the claimed 3600dpi reduces, as is common in scanners, to (say) 1800dpi in the other direction that becomes 8.7m dots. But, either way, the spec states 5 mega pixels! ignore that & carry on Each dot contains 3 values - one for each primary colour. The combined colour value at each dot is stored in 48 bits = 6 bytes So 17.35 million dots therefore needs 17.35m x 6 bytes of storage = 104MB! Which, again, doesn't seem to square with a stated 5M pixels. There must be something very basic I am misunderstanding, but what is it? No doubt the machine will make heavy use of data compression. To what extent does that explain the sums? No, because compressed files are always measured in so many bytes, not pixels. To take another example, my digital camera takes 6.3 megapixel images. At 24-bit depth (the usual) the image file is 18 megabytes. At 48-bit depth the file is 36 megabytes. Both files are still 6.3 megapixels. When the files are saved as a Jpeg compressed file, the file size is around 2 to 4 megabytes. I would guess that the 5 pegapixels mentioned in the ad should be 5 megabytes, which makes more sense, and implies a fairly heavy jpeg compression. However, the bottom line is, as Alan intimated, that at 40 pounds, the scanner has to be junk. Prices for recognised good scanners are about 10 to 15 times that price. It's a toy. Be pleased you asked before doing your 40 quid. Colin D. BTW the scanner looks cheap but in the UK ALDI special offers (there's a new lot every week & when they're gone, they're gone) are often of above average quality. TIA for an explanation |
Thread Tools | |
Display Modes | |
|
|
Similar Threads | ||||
Thread | Thread Starter | Forum | Replies | Last Post |
WTB: negative/ slide scanner | apkesh | In The Darkroom | 0 | March 17th 04 02:30 AM |
NIKON LS-30 Coolscan III slide/negative scanner | [email protected] | Darkroom Equipment For Sale | 0 | January 17th 04 01:05 AM |
NIKON LS-30 Coolscan III slide/negative scanner | [email protected] | Digital Photo Equipment For Sale | 0 | January 17th 04 01:05 AM |