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Jpeg Standard profile for 400D

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Offline vit40

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Jpeg Standard profile for 400D
« on: 05 / January / 2011, 04:41:56 »
Several months ago, I started a dng profile generator project, to make camera dng profiles for my Canon compacts, because they are not supported by Adobe and existing calibrations were not especially good. You can find a thread about that in RAW Shooting and Processing section of this forum

Since I also have 400D, I reused part of the code to make a profile for 400D. Adobe produced camera profiles for this camera, but they are slightly inaccurate, so I wanted to find out is it possible to do better. Of course, dng profile editor wasn't the right tool for this

I made only standard profile, because I don't use other profiles. Here it is

To get the same (or almost) result as from camera, you have to set

- white balance  as shot
- exposure       -0.25
- brightness      +50
- contrast         +25
- blacks             0
- tone curve     medium contrast
- color space    sRGB

Calibration was made with Standard picture style set on the camera, default saturation, contrast and tone, in sRGB color space

Improvements over calibration by Adobe are:

1. 0.25 EV more highlight headroom. Adobe assumes baseline exposure 0.25 for 400D, so upper 0.25 EV of raw data is simply truncated by using Adobe camera profile. You can recover it by recovery tool, but it changes colors. But, when using this profile, exposure slider should be moved to -0.25, if you want the same result as from the camera. Unfortunately, Adobe didn't provide more elegant solution for this so far

2. Conversion from raw color space to Photo Pro color space and rendering is done using lookup table in profile only, like in some latest profiles by adobe (550D for instance). In original camera standard profile for 400D, conversion is done using forward matrix and rendering using lookup table. That solution had several issues, like some color gamut truncation in blue range and unwanted hue shifts in blown highlights, so Adobe changed the workflow lately

3. There was some banding in red range when using original profile, which is considerably reduced by using bigger lookup table, of size 90x16x16 (Adobe used that size for 550D profiles). Lookup table in original profile has size 36x16x16, so the file was less then half the size

4. Dark tones are better matched to jpeg than in original profile, because in original profile, lookup table points for darkest level aren't calibrated at all, but just a copy of the level above it. Adobe didn't address this so far, even in the latest profiles

5. Other colors are also better matched to jpeg. But, since calibration is done in sRGB, output is limited to sRGB (Canon uses a kind of perceptual rendering). So if you set the camera to AdobeRGB, you won't get the same colors in ACR with this profile, even if you set Adobe RGB in ACR

« Last Edit: 05 / January / 2011, 08:43:59 by vit40 »


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