Hello. Some Xsane/Sane-Epson notes: Summary: I want save the scanned image "as is" without effects and without value range clippings at bottom or top. The design of sane/xsane seems to make this difficult to optain. I need help in finding suitable settings.
I would like to have all Epson developers documentations? Where I may download them? I suggest to read the rest of the mail paragraph by paragraph. -*- There should have "unsharp off" switch. Sharpness = 0 or = "normal" tells nothing. Elsewhere "normal" may mean "unsharp masking on"!! What sharpness = 0 or = "normal" means in Sane? Is it "off"? Gamma option could be named better. It took me a while to understand that "default" means gamma on and that "brightness" controls the gamma curve. Does "user defined" mean gamma = 1.0, and that any gamma then can be added at enchangement phase? I.e., the raw image has no gamma applied. Where the user defined gamma curve is defined? xscanimage provides the gamma curves but xsane does not. With or without gamma, I have got only two cases: 1. xsane histogram clips the top values, gimp histogram clips the top values of the filed image 2. xsane histogram does not clip the top values, gimp histogram clips the top values of the filed image That is, as case 2. indicates, there is also something wrong in the save operation. Check screenshot of gimp and xsane histograms at "http://www.funet.fi/~kouhia/histograms.pnm";. It shows the case 2. Check screenshot of MS Win driver histogram at "http://www.funet.fi/~kouhia/winhisto.pnm";, and compare it to above histogram image. When scanning images, no clipping should occur; values should fit in range 0-255 (or 0-65535) with some quard space at bottom and top. "winhisto.pnm" shows a good fit. However, could it be that MS Windows driver soft-limit the values to below the value 245 (or such; see the "winhisto.pnm")? I.e., the gamma curve bends slowly to the value g[255] = 245. I found following in a saved image: XSane settings: resolution_x = 200.0 resolution_y = 200.0 gamma IRGB = 0.00 8.66 0.00 8.31 brightness IRGB = 8.3 8.3 8.3 8.8 contrast IRGB = 0.0 8.3 0.0 8.2 Those gamma etc. values looks rather odd. Why I and G are 0.0? What represents the values 8.66 and 8.31? Who set them? I used gamma 1.0, brightness 0.0, and contrast 0.0. "user defined" and no color correction in epson options. Xsane code reveals that the gamma correction is always performed. How do I set that the scanner is not doing the correction and that xsane is not doing the correction? If the gamma = 1.0, is the gamma table really of the form g[0] = 0, g[1] = 1, ..., g[255] = 255 --- that is, no rounding errors whatsoever. When gamma is not in use, there should be "exposure" control for the scanner. Why there is no such control? MS Windows driver seems to have such a control. I forced "F5" epson type/level, but no exposure control appeared in Xsane GUI (only the bay control appeared additionally). Can exposure adjusted from a hardware knob or such? If nothing else helps to the overexposure (clipping), that is. Histogram seems to not work properly; I changed the brightness of the epson options but while the image changed, it had no effect to the histogram. Could be separate bug. -*- The xsane/sane-epson application is quite confusing. How about clearly separating (1) the operations done inside the scanner and (2) operations done in sane-epson driver, and (3) operations done in xsane? For example, gamma/color curves would be set separately for the scanner and for the driver, and for the frontend application. (Frontend application could warn if user has set gamma curves in multiple places.) In any case, now it is quite difficult to understand, say, are gammas curves applied or not; are they applied for the display only or not. This triple module system would not be any more difficult to understand, but would help in understanding what various effects are --- at least, I suspect that some patented effect in the scanner is better than equivalent effect in an open source application. The triple module system would separate these different brands of algorithms clearly. A menu entry "save the raw image" would help in making sure xsane does not save the enchanged image. It is now too easy to save image calibrated for CRT screen with gamma and other effects applied. It is surprise that people want to immediately process the image for screen or printing whatever. These processings cannot be undone. If the raw image is archived, images could later be processed for different screen and different printers. There seems to not have an image viewer which can do the screen gamma correction and other display effects on-the-fly so that users could convenietly work with archived raw images. For example, sharpen effect helps greatly in reading textual images, but never I would want archive pre-sharpened images. Here is a diagram of the ideal system for me: -------------------- ------------------- | scanner without | | backend without |---> "save raw image" | effects but with |--->| effects and |---> xsane enchangements | optimal exposure | | processings |---> print tool -------------------- ------------------- and --------- | raw |-------> image viewer with effects | image | | file |-------> print application --------- (Note: "raw" image in above does not mean a raw image format; it means the raw image loaded from the scanner.) The optimal exposure would mean that all intensity values fits to the range 0-255 (0-65535) and that the values are as close as possible to the values read from A/D converter (whatever). Best regards, Juhana
