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Author Topic: DCamProf - a new camera profiling tool  (Read 767299 times)

torger

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Re: DCamProf - a new camera profiling tool
« Reply #760 on: August 27, 2015, 01:53:56 pm »

I am new to DCAMPROF.

I just follow the instructions below, X100.DNG is from DNG converter.

dcraw -v -r 1 1 1 1 -o 0 -H 0 -T -W -g 1 1 X100.DNG
scanin -v -G 1.0 -dipn X100.tif ColorChecker.cht cc24_ref.cie
dcamprof make-profile -w all 1.5,1,8,2,1 -l 0.1,0.1 X100.ti3 profile.json
dcamprof make-dcp -n "Fujifilm Finepix X100" -d "DCAMPROF" -t linear profile.json DCAMPROF_X100.dcp

Finally,I import DCAMPROF_X100.dcp to LR, and export to tif.
I make crop to show CC24 area. Is this ok for the calibration results? White balance looks fine here.
But it looked somewhat low contrast, dark and flat. Anything I am doing wrong here??
Thanks for help.


By my eye it seems correct. However as you do "-t linear" you get a colorimetric profile without a curve, which indeed looks low contrast, dark and flat. A flat colorimetric profile is good when you do reproduction work (copy artwork etc), but not so nice for general purpose photography.

To get a default curve embedded change your make-dcp command to:

dcamprof make-dcp -n "Fujifilm Finepix X100" -d "DCAMPROF" -t acr profile.json DCAMPROF_X100.dcp

If you want to fine-tune to match the contrast and brightness of the bundled profile you can "steal" the curve and baseline exposure from the bundled profile, or you can design your own.
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torger

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Re: DCamProf - a new camera profiling tool
« Reply #761 on: August 27, 2015, 02:07:16 pm »

Here's a more detailed description of matching the curve / baseline exposure. It's from a tutorial I'm working on but haven't published yet:

Choose a tone curve and exposure offsets

When we reproduce a scene on screen or on paper the luminance is typically lower which leads to that the eye experience the image as lower contrast, a bit dull even, this even if the (mid-tone) contrast is 100% accurate. This is a normal perceptual phenomenon and the solution is as old as photography: we apply an S-shaped contrast
curve. In digital photography there's more compression of highlights than shadows as that suits the linear sensor behavior better, but the principle is the same. By compressing highlights and shadows we get increased midtone contrast so the whole image seems to have higher contrast, and we can get a better perceptual match with the original scene.

A less known side effect of applying contrast is that the appearance of colors change. In human vision contrast and color appearance is tightly connected which means that if we want to retain the original color appearance when changing global contrast we must make some adjustments to the colors. Broadly speaking higher contrast requires higher saturation, and increased saturation is a natural side-effect of a basic RGB curve which is what's been traditionally used in digital photography. However an RGB curve will overdo saturation and it will also distort color so it's far from perfect, in fact there is still today no broadly used standard curve that is reasonably
perceptually accurate. (It's actually not possible to make it 100% accurate, as that would require image-dependent local adjustments which a camera profile can't do.)

DCamProf provides its own custom curve, a "neutral tone reproduction operator" to make it possible to embed a curve without distorting color appearance, and I think this is one of the more important features. Without that it doesn't matter how accurate we make our profile, as soon as we apply a curve in the raw converter the perceptual accuracy goes down the drain. And no, applying contrast in the Lab lightness channel or HSV value channel will not cut it (although it may work well for smaller adjustments or for creative effect). As I also contribute to the RawTherapee project, there's now actually a "perceptual" curve there which is based on DCamProf's
neutral tone reproduction operator, so for RawTherapee you can provide a profile without a curve and instead apply it using the builtin curve adjustment, but as far as I know RawTherapee is unique in this aspect. For convenience you may still want to embed it in the profile though.

For a longer more detailed discussion on how tone curves affect color, see http://www.ludd.ltu.se/~torger/dcamprof.html#tone_curves tone curve section in DCamProf's reference manual.

Anyway, in order to make our profile fit for all-around photography we need to have an S-shaped tone curve to apply some contrast. So which shape to choose? With Adobe Camera Raw and the DNG reference code comes a standard curve which is used in many of Adobe's own profiles and it's also available as a built-in choice in DCamProf. It will provide a good result and if you don't have some special need I suggest using that (<tt>-t acr</tt> provided to make-dcp).

The typical reason to want some other curve is to better match the look of in-camera JPEGs. This can indeed be important. With Adobe's curve the look may become significantly brighter or darker than the in-camera JPEG, and while it's okay if you will "expose to the right" (ETTR) manually anyway (common for planned photography shot from a tripod), the camera's auto exposure is of course tuned for the in-camera JPEG curve. That is to get good results without adjustments you need the curve to match what the camera expects.

For DNG profiles there are actually three parameters for this, the curve itself, a baseline exposure offset and a black render tag. The DNG file itself can also contain a fixed baseline exposure which is added to the offset in the profile, at least if you're using Adobe's products. The exposure offsets and black render tag may or may not be
supported by your favorite raw converter, so they may not be usable. The curve is generally supported though if the converter has a decent DNG profile support.

The baseline exposure offset is sort of redundant as a curve can also include an exposure offset (it's just the average slope of it), but if the offset is large the curve gets an extreme shape which is hard to design so in that case it can be easier to separate them. The same can be said about the black render tag. That tag does not quantify an offset, it just tells the raw converter if it should make an automatic black subtraction (that is clip away darkest shadows if there is no detail there) or leave as is.

Matching the curve used by the camera

How to get the curve from your camera? Obviously we could shoot a backlit step wedge and make a precise measurement-based match that way, but there's no real need to make an exact match, we won't have the exact camera appearance anyway concerning color. We just need to make a curve that has about the same brightness and contrast as the camera so when we use the camera's auto exposure we get a good result.

To do this I think visual matching works well, and you can use RawTherapee for that.

  * If possible set the camera to write JPEGs together with the raw.
      * If possible set color space to sRGB, unless you know what
        you're doing and can display the JPEG properly with AdobeRGB (or
        whatever the other color space is).
  * Shoot basic sunny outdoor scenes with both highlights and shadows.
      * It should be contrasty, but avoid back light.
      * Avoid extremely saurated colors as they will exaggerate
      differences between profiles and make it harder to match
      curves.
      * Preferably shoot more than one so you have a few to test.
  * If you're using a DNG workflow, convert the raw to DNG using
  your chosen DNG converter (it may add an baseline exposure offset
  tag).
      * If you use DNG files with non-zero baseline exposure and you
        intend to honor that (as Adobe Camera Raw does), make sure
        you apply corresponding exposure in RawTherapee (at the time
        of writing RawTherapee ignores any baseline exposure in the
        DNG file).
  * If you couldn't get JPEGs directly, use for example exiftool to
  extract the embedded preview image from the raw. If the color space
  is not sRGB you may need to attach a profile to it (usually AdobeRGB)
  which can also be done with exiftool.
      * Make sure you get the camera's preview, not a re-rendered
      preview made by your DNG converter if you're using that.
      * exiftool -b -PreviewImage -w _preview.jpg _MG_0715.CR2
      * exiftool "-icc_profile<=AdobeRGB.icc" _MG_0715_preview.jpg
  * Open the raw file in RawTherapee and bring up the JPEG side by
  side on screen, either by launching another RawTherapee instance and
  open the JPEG there or bring it up in an image viewer.
  * Apply (Neutral) processing profile so you get a clean start.
  * Fold out "Tone curve 1" by choosing "Custom" (which is a spline curve).
      * Curve type can be any, some are more saturated than others,
      try one that matches the look of the camera JPEG the best (makes
      it easier to match curve, optionally use the saturation slider
      to make a better match.
      * You can make the panel wider to make the curve larger and
      easier to fine-tune.
  * Add three control points to the curve, and make an S-shape
  similar to the one shown in the screen shot, it's a good starting
  point.
  * Look at the darkest shadows in the JPEG and see if it's likely
  some black subtraction has been made. If so match as well as
  you can with the "Black" slider.
  * Is the image considerably darker? Adjust "Exposure compensation"
  to make a better match.
      * Small offsets like 0.1-0.2 stops can typcially be solved by
      brightening using the curve, while above that then it's better
      to have an exposure compensation.
  * Fine-tune the curve to match by moving and adding handles. Try
  to keep down the number of handles, the more you have the harder it
  becomes to make it smooth.
  * Save the curve to an .rtc file.
      * The .rtc file can be used directly by DCamProf.
  * Write down if you had to adjust the black slider and how much
  exposure adjustment you needed if any.

It is indeed hard to make an exact match, but it's not important. This is just about getting predictable results from the camera's auto exposure. It's more important that you like the shape of the curve, that it has suitable contrast and shadow compression. I often find it desirable to keep a little more shadow detail than camera JPEGs do for example.

If you had to adjust black subtraction and/or exposure you have some choices to make. Either you make a processing profile for your favorite raw converter that contains these presets, or you include the settings in your DNG profile. What is best depends on the feature set of the raw converter (if it supports the offset DNG profile tags or
not, and how presets are managed) and what you prefer.

You can also try to reshape the curve to compensate for any black subtraction and exposure offset.

If we start with black subtraction this can be 100% mirrored with a curve, but it will then unrecoverably cut shadows. It's better to just add an extra handle for the darkest shadows and compress a bit more there. Your will undoubltly get a less contrasty look in the shadow range this way, but also more shadow detail which you may
prefer anyway.

The exposure offset can also be mirrored with the curve but again not without unrecoverable clipping, so you could instead just increase highlight compression to increase brightness overall to match.

In general I think embedding an exposure offset in the profile makes more sense than black subtraction, especially since black subtraction cannot be set as a specific number but the result will instead vary between raw converters. My recommendation is thus combine the curve with an exposure offset if it makes sense, but try to avoid black subtraction.

The total baseline exposure should rather not be negative. That is the file's baseline exposure plus the profile's baseline exposure offset should be zero or positive. If you make it negative you will force the raw converter into showing potentially clipped highlights which is not a good default.

Notes on baseline exposure

The DNG specification has two baseline exposures, one that is stored in the DNG file itself, "baseline exposure", and one in the profile "baseline exposure offset". The latter was introduced in version 1.4 of the standard, prior to that baseline exposure could only be embedded in the DNG.

This is an unfortunate situation, if you ask me it's a poor design choice made by Adobe. The baseline exposure is 100% related to the profile, as it will depend on the curve shape which number you want. Naturally Adobe's DNG converter will embed a baseline exposure tag with its DNG files that is adapted to work with Abobe's proprietary profiles, and it may not really suit your profile.

It would be much better if the DNG profile itself specified all the baseline exposure, which it can with the new baseline exposure offset tag which is stored in the profile. Unfortunately the specification says that it shouldn't override the DNG file tag, but just adds an offset to it and that is what happens in Adobe's products. This means that you still need to know what value your DNG converter will put there, and if your raw converter cares about the value. Many raw converters can do both DNG and native raw. The native raw file has no baseline exposure offset, meaning that a DNG profile may need a different baseline exposure offset when used with native raws than when used with Adobe's DNGs.

I recommend to test your favorite raw converter to see how it reacts to baseline exposure, it's not certain that it will care about the value in the DNG file. It's not unlikely that you may need one offset for Adobe's products and a different offset for others.
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AlterEgo

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Re: DCamProf - a new camera profiling tool
« Reply #762 on: August 27, 2015, 02:27:54 pm »

than when used with Adobe's DNGs.
shall be added "or with Adobe converters"... they (ACR/LR) have that component also hardcoded in their code.
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Iliah

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Re: DCamProf - a new camera profiling tool
« Reply #763 on: August 27, 2015, 05:00:26 pm »

Usual way to get the curve is to take a series of of bracketed shots of some more or less uniformly lit smooth surface (a computer screen out of focus is a good target), and the curve can be constructed easily from that.
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Bip

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Re: DCamProf - a new camera profiling tool
« Reply #764 on: August 27, 2015, 05:13:10 pm »

For historical reasons RT always use its hard-coded color matrices for the white balance calculations, never the DCP color matrix (the RT white balance model needs some re-work, but noone's had time to do it yet).
For RT, I think, since version 3.xx, white balance is calculated on a range from 4000k to 25000k, ยง White balance http://50.87.144.65/~rt/w/index.php?title=Color_Management_addon

Adobe uses the DCP of course. Still if you use "as shot" you should see the same result in RT as in Lr, even if the stated color/temp is different, and this is the result I get. Have you tried "As Shot" white balance? Do you get the same result in RT as in Lr, as I do? If not you may have some other issue.

Yes, with "as chot" the display of white balance with RT(any dcp (or icc) profil ) and Lr (profil Adobe Std) is the same (delta 30k, it is negligible) ,  with the profil made with Dcamprof the value of white balance change (~7000k et hue 150).


Only when you have set a manual temp/tint Lr will use the color matrix "in reverse" to figure out the multipliers and then the color matrix will matter, that is a different color matrix will result in a different tint of the image.

I undestand the same thing as you,  except that :

-With a "normal ColorMatrix" dcp profil with Lr, it is ok
-with profil made dcamprof, the white balance is done, but hue stay saturated.

By using json2dcp/dcp2json and a text editor you can experiment with extracting the color matrix from Adobe's bundled profile and put that into the DCamProf profile. Then you should get the exact same white balance as the Adobe profile, but the color rendition is still completely DCamProf, as that is only affected by forward matrix and LUTs.

Really old DCPs had only a color matrix (no forward matrix), and in that case the color matrix also affected the color rendition, but as soon as you have a forward matrix, the color matrix is only used for calculating white balance multpliers from temp/tint or calculating temp/tint from the raw-embedded as-shot multipliers.
yes I am agree. I do a profil dcp with DNG profil editor with a cc24 shot with the same light (flash). I swap the ColorMatrix in the profil made with Dcamprof, now it is ok, white balance and hue run normally.

Below you will find the matrix.

ColorMatrix Dcamprof that dn't run
  "ColorMatrix 1": [
    [  1.455000, -0.315800, -0.121900 ],
    [ -0.607600,  1.379900,  0.208200 ],
    [ -0.135800,  0.218600,  1.022600 ]

ColorMatrix DNG adobe editor (D65)
"ColorMatrix1": [
    [  0.813900, -0.217100, -0.066400 ],
    [ -0.874800,  1.654100,  0.229600 ],
    [ -0.192400,  0.200800,  0.809300 ]

I dn't know, if this matrices can help you to understand the matter (?). I searched without finding, may be, there are an overflow with the matrix calculated with Dcamprof?
« Last Edit: August 27, 2015, 05:28:56 pm by Bip »
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torger

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Re: DCamProf - a new camera profiling tool
« Reply #765 on: August 28, 2015, 02:52:46 am »

Usual way to get the curve is to take a series of of bracketed shots of some more or less uniformly lit smooth surface (a computer screen out of focus is a good target), and the curve can be constructed easily from that.

Interesting! I'll try that technique.
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torger

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Re: DCamProf - a new camera profiling tool
« Reply #766 on: August 28, 2015, 02:55:58 am »

Thanks for testing Bip, I'll do some debugging of the color matrix calculator in DCamProf when I get time and opportunity, hopefully soon.

As the color matrix is not used at all when rendering ICC profiles, or when using (single-illuminant) DCPs in RawTherapee and I'm not a Lightroom/ACR user I haven't given it much test so far.
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Bip

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Re: DCamProf - a new camera profiling tool
« Reply #767 on: August 28, 2015, 04:05:42 am »

Thanks for testing Bip, I'll do some debugging of the color matrix calculator in DCamProf when I get time and opportunity, hopefully soon.

As the color matrix is not used at all when rendering ICC profiles, or when using (single-illuminant) DCPs in RawTherapee and I'm not a Lightroom/ACR user I haven't given it much test so far.
May be, it is not a bug of Dcamprof, but an incompatibility with Lr / Acr.
Thank you for your help to find a solution.
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torger

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Re: DCamProf - a new camera profiling tool
« Reply #768 on: August 28, 2015, 07:29:32 am »

May be, it is not a bug of Dcamprof, but an incompatibility with Lr / Acr.
Thank you for your help to find a solution.

I've done a few experiments, not running on Lr yet though as I have that on a different box in a different house. Anyway I haven't so far discovered any error.

In any case even if there is an error and I fix it, the color matrix result can differ quite much. Although the color matrix is white-point preserving (that is no compromise is made to match the white-point, it's the only color that is matched exactly), the raw RGB values for white will differ depending on the exact shape of the illuminant spectrum. (The actual numbers between two matrices can differ quite a lot too, even if they would map white to the exact same number, as the matrices map other colors too and can do that very much different.)

In any case as we cannot get the exact setup Adobe has used, DCamProf will come to a different conclusion, and thus estimate temp/tint a bit differently. This means that in Lr/ACR for all other white balances than "as shot" you will get a white balance shift. If you don't want that to happen there's an easy fix though, just copy Adobe's color matrix and put it into DCamProf's json profile, and re-run make-dcp.

What surprised me and made me suspect a bug is that here is quite large differences in temperature estimation, like in my example 4800K for Adobe and 5500K for DCamProf. I would have guessed the temperature difference should be smaller, so it's that point I'm investigating. But as said, you can't get a 100% match, if there is a bug I would still expect that at least +/-200K would differ in the normal case. So if you don't want your new custom profile to affect the white balance of your old adjusted photos when you change profile, you need to do the copy trick.
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torger

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Re: DCamProf - a new camera profiling tool
« Reply #769 on: August 28, 2015, 10:05:32 am »

An example for a 5D mark II;

For a daylight shot:
As shot temperature, according to ACR with bundled profile: 4803K (tint 1)
As shot temperature, according to DCamProf profile generated with D50 and SSF: 5762K (tint 20)
As shot temperature, according to DCamProf profile generated with Solux ~5500K and test targets: 5123K (tint 6)

Canon themselves call the "as shot" temperature "5200K", and the white balance multipliers are 2.14,1.00,1.68

Looking at DxOmark measurements, the D50 white balance is stated as 2.57,1.00,1.44
DCamProf D50 white balance based on SSFs is 1.93,1.00,1.78
DCamProf D50 Solux/targets: 2.12,1.00,1.72
Adobe bundled profile D50: 2.22,1,1.68

The values are all over the map. DxOMark measurement indicates that the as shot daylight settings is a lower temperature than D50. The SSFs I've got leads me to much different result (the quality of the SSF is unclear though), and my DCamProf profile made with traditional methods is in most agreement with Canon's own labeled temperature.

So far I have not found any error in the calculation process, and if it where I would suspect gross color errors as the forward matrix is calculated the same way as the color matrix.

Could it be that all those differences are related to different calibration illuminants?
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Iliah

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Re: DCamProf - a new camera profiling tool
« Reply #770 on: August 28, 2015, 10:40:40 am »

The numbers of CCT and Tint strongly depend on the light spectrum, and the way the matrices are calculated;  _never_ I saw a CCT in a converter in good agreement with direct measurements, or good inter-converter agreement for that matter. CCT and Tint are convolutions, and as it is with the ordinary maps, they may be relatively accurate (direct measurements of distances/angles) for a close proximity, but not so for a larger vicinity.
WB coefficients can be easily close for very different light, but at least they are directly transportable between converters (that is, if a converter allows such input). That is why we don not use CCT in RPP, in spite of all user demands. Why chase something something that does not make any sense?
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torger

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Re: DCamProf - a new camera profiling tool
« Reply #771 on: August 28, 2015, 11:16:33 am »

The numbers of CCT and Tint strongly depend on the light spectrum, and the way the matrices are calculated;  _never_ I saw a CCT in a converter in good agreement with direct measurements, or good inter-converter agreement for that matter. CCT and Tint are convolutions, and as it is with the ordinary maps, they may be relatively accurate (direct measurements of distances/angles) for a close proximity, but not so for a larger vicinity.
WB coefficients can be easily close for very different light, but at least they are directly transportable between converters (that is, if a converter allows such input). That is why we don not use CCT in RPP, in spite of all user demands. Why chase something something that does not make any sense?

Sounds reasonable. I've noticed this issue with temperatures before, but I haven't really known exactly how unreliable it is.

The problem with Lr/ACR is that if you have edited a file with a custom white balance, they store the temp and tint number, not the white balance multipliers. So when you change profile, it probes the profile with the stored temp/tint to find out which white balance multipliers that lead up to that temp/tint for that profile, which as shown before lead to entirely different multipliers and you get a white balance shift.

Seems to me that this is a design problem with DCP/ACR which Lightroom/ACR users just have to live with. I think I'll document the work-around (copy color matrix from existing profiles) in the documentation.
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Iliah

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Re: DCamProf - a new camera profiling tool
« Reply #772 on: August 28, 2015, 11:19:39 am »

> The problem with Lr/ACR is that if you have edited a file with a custom white balance, they store the temp and tint number, not the white balance multipliers. So when you change profile, it probes the profile with the stored temp/tint to find out which white balance multipliers that lead up to that temp/tint for that profile, which as shown before lead to entirely different multipliers and you get a white balance shift.

Yes, that's how it is.

A plugin to Lr that adds WB coeffs to XMP files and reads those coeffs back is possible.
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AlterEgo

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Re: DCamProf - a new camera profiling tool
« Reply #773 on: August 28, 2015, 12:01:24 pm »

I think I'll document the work-around (copy color matrix from existing profiles) in the documentation.
\
may be add a command line parameter to dcamprof itself to automate that
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torger

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Re: DCamProf - a new camera profiling tool
« Reply #774 on: August 28, 2015, 02:21:55 pm »

I've just released 0.9.4

I did not find any bug in the color matrix calculation so I assume that the fairly large differences we see depends on other natural factors. So no changes regarding that.

As suggested by AlterEgo I did add a new parameter, -m, to make-dcp so you can automatically copy color matrix/matrices from an old profile if you want to keep the exact same color temp estimation.

The big work is on ICC profile LUT generation which has been reworked to avoid high saturation color artifacts mainly in Capture One. Although the algorithm is really slow and not so elegant in terms of implementation, it does seem to work just fine. So to the best of my knowledge DCamProf is now mature enough to make really high end Capture One ICC profiles that work in the same way as the native profiles.

Get it at the usual place.
« Last Edit: August 28, 2015, 02:47:53 pm by torger »
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AlterEgo

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Re: DCamProf - a new camera profiling tool
« Reply #775 on: August 28, 2015, 02:47:03 pm »

0.9.4 build for Windows (mingw = dcamprof.exe + libgomp_64-1.dll + HTML & PDF manual / = copy of Torger's web page and the same converted to PDF /) : https://app.box.com/s/hxy4q0rzi59jhxdv4aqrefl5gd1p8xu1
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Bip

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Re: DCamProf - a new camera profiling tool
« Reply #776 on: August 28, 2015, 04:43:00 pm »

I've just released 0.9.4

I did not find any bug in the color matrix calculation so I assume that the fairly large differences we see depends on other natural factors. So no changes regarding that.

As suggested by AlterEgo I did add a new parameter, -m, to make-dcp so you can automatically copy color matrix/matrices from an old profile if you want to keep the exact same color temp estimation.

The big work is on ICC profile LUT generation which has been reworked to avoid high saturation color artifacts mainly in Capture One. Although the algorithm is really slow and not so elegant in terms of implementation, it does seem to work just fine. So to the best of my knowledge DCamProf is now mature enough to make really high end Capture One ICC profiles that work in the same way as the native profiles.

Get it at the usual place.

Thank you, I downloaded the 9.4
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Bip

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Re: DCamProf - a new camera profiling tool
« Reply #777 on: August 28, 2015, 04:46:32 pm »

@ AlterEgo

Can you say me :

What kind of virtual target  (CC24, CC digital SG* or other) you use? when you do profile with the SSF data from the camera.
Do you take generic or measured spectral datas to simulate virtual target?

For CC Digital SG, I dn't find the spectral datas. (It seems that Xrite did not given them)

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AlterEgo

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Re: DCamProf - a new camera profiling tool
« Reply #778 on: August 28, 2015, 05:37:35 pm »

For CC Digital SG, I dn't find the spectral datas. (It seems that Xrite did not given them)

GM data from PM attached
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AlterEgo

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Re: DCamProf - a new camera profiling tool
« Reply #779 on: August 28, 2015, 05:41:17 pm »

What kind of virtual target  (CC24, CC digital SG* or other) you use?

for a start you can use CC24 data embedded into DCamProf itself... I test on that small virtual target initially.
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