Bits vs. Resolution

Discussion in 'Digital Darkroom' started by bob_bornfriend, Nov 3, 2014.

  1. I'd appreciate advice on how much emphasis to place on color depth vs. resolution. I've zeroed in on a mid-priced scanner for prints from Epson or HP. The new Epson V550 features 6400x9600 resolution with 48 bits. The also new HP G4050 features 4800x9600 resolution with 96 bits, 6 colors. Both are equally priced.
    Which is more important from a practical viewpoint?
     
  2. More important might be the optical resolution, the max youi've listed is for an interpolated resolution, much less important. The Epson has an optical resolution of 6400dpi while the HP is listed at 4800dpi. The other important spec is the optical density, the Epson is listed at 3.4, can't find one for the HP. I have no idea what 96bit contributes to quality.
     
  3. Keep in mind that it does no good to scan a print at a really high resolution if the detail isn't there in the print in the first place, which it probably isn't. 2,000 spi (samples per inch) is probably way more than you need for a photographic print. Higher usually doesn't hurt, but it takes longer and adds nothing.
     
  4. Many (most?) of us who shoot RAW with our DSLRs get our files at a depth of 14 bits, use a RAW converter to give us 16 bits per colour per pixel (that's 48 bits), and edit our pictures at that same bit depth in our choice of photo editing software, most of which don't support more than 16 bits times 3 colours per pixel other than for HDR. So if you get a scanner that offers more than 48 total bits per pixel, or more than 3 colours per pixel:
    • is it actually going to be of practical benefit to try to extract more data from a print than most cameras, even professional ones, can extract from an actual scene?
    • what software are you going to use that can actually utilize that many bits of data?
     
  5. Excellent points, Steve. Now that I think about it, I don't believe my current software handles the extra bits. Maybe some future version will, though. Is it worth worrying about? Probably not.

    Thanks to all for their responses.
     
  6. The optical resolution determines how large the print can be. The bit depth determines how much the exposure and color can be adjusted before posterization occurs.
    Specifications for scanners are often wildly optimistic. These scanners use a linear array of micro lenses, for which the field of view overlaps. The useable resolution is typically about 1/2 the stated optical resolution. With regard to bit depth (48 bits = 16 bits/channel), the scanner may record 16 bit words, but the top two or three bits may be meaningless. In fact, any word larger than 8 bits is recorded in 16 bit format, otherwise known as double precision.
    That said, Epson scanners tend to have better performance for photographers than those by HP, which are more business oriented (documents and such). The mechanical quality in more expensive Epson scanners is usually very good. I have an Epson "Expression" 1600 by my desk, with a lighted cover for transparencies (and film). I've had it for twelve years and have used it daily. Unlike cheaper scanners, the Expression has a single process lens with a dual focusing range for film in holders. The true resolution is close to 1600 dpi, limited by the pitch of the linear sensor array and stepping motor. It also cost $1100 in 2002.
     
  7. The optical resolution determines how large the print can be. The bit depth determines how much the exposure and color can be adjusted before posterization occurs.
    Specifications for scanners are often wildly optimistic. These scanners use a linear array of micro lenses, for which the field of view overlaps. The useable resolution is typically about 1/2 the stated optical resolution. With regard to bit depth (48 bits = 16 bits/channel), the scanner may record 16 bit words, but the top two or three bits may be meaningless. In fact, any word larger than 8 bits is recorded in 16 bit format, otherwise known as double precision.
    That said, Epson scanners tend to have better performance for photographers than those by HP, which are more business oriented (documents and such). The mechanical quality in more expensive Epson scanners is usually very good. I have an Epson "Expression" 1600 by my desk, with a lighted cover for transparencies (and film). I've had it for twelve years and have used it daily. Unlike cheaper scanners, the Expression has a single process lens with a dual focusing range for film in holders. The true resolution is close to 1600 dpi, limited by the pitch of the linear sensor array and stepping motor. It also cost $1100 in 2002.
     
  8. @Bob, none of those scanners can attain even 50% of the resolution they claim. Yes, they deliver the pixels, but not the resolving power. It's something you'll have to read a lot about in order to understand.
    As to the bit depth, none of them can certainly give you anything beyond, say, 36 bits. Yes, they can deliver the bits, but not the precision.
    In short, those specs are completely meaningless.
     
  9. Just to keep things accurate - the Epson does not have an optical resolution of 6400. There is a difference between the number of pixels that can be generated and the number of line pairs that it can resolve on something like that Air Force test target...
    Accounts vary depending on technique but the Epson 750 can only resolve somewhere between 1900 and 2400 ppi.
    I would choose the Epson over the HP. I have a drum scanner and thankfully don't have to make that choice...
     
  10. Listen to Lenny and Edward.
     
  11. 6400x9600 resolution​
    Hogwash. It's some kind of theoretical figure; the actual resolution is much lower. I have measured the V500 with a good target. The actual resolution achieved is 1300 ppi in one direction and 2000 ppi in the other. I'm sure the V750 is better, others have quoted 2000 to 3000 ppi.

    But, you say you are going to scan prints. I believe any of these scanners would do an excellent job in scanning prints where you don't need these super-high resolutions. And, while you want a good DMax for scanning negatives or chromes, I don't think it's so important for prints.
     
  12. My experience with Epson scanners has been far better than with HP scanners over the years. It's like Epson designs for the artist and HP designs for the businessman, honestly.
     
  13. Don't imagine for a minute that Epson gives a damn about you. It's all about the money. They are a very large and very nasty company when it comes to their corporate behavior. They are not out for artists, that's for sure...
     

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