spherical aberration ?

[thomas]

Hello,

It is highly unprobable that this topic does not already exist, but I was unable to find it (maybe because I do not know the right english terminology (I'm french)) -> I apologize.

So, my problem is with the digital camera : when I take a picture, the center of the book's page is good, but the corner are fuzzy (see picture below). Not that fuzzy, but sufficiently for any OCR I've tried to be confused (in the better case, I got bold fonts - but usually I got many mistakes).

Is the digital camera too bad (it is a sony DSC WX1) ? Or shall I just tune it ? Or take the picture from farther or closer, playing with the zoom (for this picture : the camera is at more or less 60cm from the plate) ?

Thank you for your help and for this great website !

[daniel_reetz]

Well, that is definitely a lens problem. Looks like the WX1 is not a particularly good camera for scanning.

But that doesn't mean you're out of luck. You can still improve these images. Will you please post a JPG of a book page that is "straight from the camera" with no modifications?

Critiquing what I can see here:

1. Your white balance is off. What is your light source, and what is your camera white balance set to?

2. Your image is noisy overall. How bright are your lights? You can gain a lot by going brighter.
a. If your camera has an aperture inside, it will go to the smaller one which should help with the corner issues a little.
b. It will also cause the camera to use a lower ISO and less noise reduction (should mean a crisper image)

3. how sturdy is your camera mount? Is there a chance that your camera is vibrating a little when the picture is taken?

[thomas]

here an image straight from the camera :

1) light source : 12 LED lamp ; white balance : for fluorescent lamp

2) the light are indeed not very bright (how many watt is not written on the lamp, but I would say some 40W). I'll try with a lighter one. How many watt do you think would be best suitable ? around 100 ?

3) not very sturdy, because Sony has the main default (I bought this camera before I even thought to do Book scanning) that they do not offer remote shutter trigger for digital compact camera (maybe there is some way to build one's, but no official one according to the reseller). However, I've also tried to shoot with the delay, just one or two pictures (since you need to reset the delay each time !) -> this does not improve a lot, so I do not think that the camera move while shooting is the main problem (although it would be surely better to remote shutter ! next time I'll bought canon !)

Thank you for your response. I'll find a bright lamp and post a new picture.

[daniel_reetz]

Yeah, I would try a standard light bulb instead of LEDs- 60 to 100W. I don't know if you can still get a tungsten bulb in Europe, but we like bulbs of this style for their sheer output power and flat spectrum. Halogen MR16 would also work.

Are they the small 5mm LEDs? Those are just not suitable for imaging because they don't have very good spectral quality.

If delay doesn't help, it's not a vibration problem. It's interesting that the problem seems to be localized to one part of the camera image - just one corner is really bad. This tells me that although you can get a lot better images with more light, the final answer might be just to avoid using that part of the image - move the book away from it.

[jgreely]

Is the digital camera too bad (it is a sony DSC WX1) ? Or shall I just tune it ? Or take the picture from farther or closer, playing with the zoom (for this picture : the camera is at more or less 60cm from the plate) ?

It's not spherical aberration, it's just not a flat-field lens, so it can't get the whole page in focus at once. Also, the DSC-WX1 doesn't have an adjustable aperture, so it can only shoot wide-open (which at the focal length you used is f/3.5); it "stops down" with a neutral-density filter.

Besides adding more light to get the ISO down from 400 to 160, a look at the PDF manual on Sony's site suggests you don't have a lot of options to manually adjust the camera settings. Definitely increase the exposure +1 EV, shut off SteadyShot, and see if using Multi-AF can find a better focus point than dead-center on the page (halfway to an edge should even out the focus). Tinkering with the DRO settings may also improve the quality, since there doesn't seem to be a way to increase contrast directly.

-j

[thomas]

I have tried with a better lamp and another digital camera (Canon G9) : this is far better with the new camera (the lamp helps, but the main improvment come from the camera). Anyway I've now moved from Moscow (Russia) to Paris (France), so I will build a new Book scanner (the first one was a try!), with new digital cameras, following advices from this forum (when I buyed my Sony camera, I had no intention to scan books with it). Than you for your help !

[Ceal]

It's not spherical aberration, it's just not a flat-field lens, so it can't get the whole page in focus at once.

The plane of the book might be slightly tilted as well. Shallow depth of field doesn't allow much leeway.

Also, the DSC-WX1 doesn't have an adjustable aperture, so it can only shoot wide-open (which at the focal length you used is f/3.5); it "stops down" with a neutral-density filter.

What a terrible design. This alone should disqualify it for copying books.