doc:appunti:hardware:canoscan_9000f_mark_ii
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doc:appunti:hardware:canoscan_9000f_mark_ii [2014/11/18 20:59] – [Invert and color balance] niccolo | doc:appunti:hardware:canoscan_9000f_mark_ii [2017/12/04 09:52] – [Web references] niccolo | ||
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==== Invert and color balance ==== | ==== Invert and color balance ==== | ||
- | This is an empirical recipe to invert and balance colors from a scanned negative strip. It is based on a three pass process: **negate**, **gamma correction** and **color level adjust**. The parameters of gamma correction and color adjust, make a specific profile suitable | + | This is an empirical recipe to invert and balance colors from a scanned negative strip. It is based on a three pass process: **negate**, **gamma correction** and **color level adjust**. The values for gamma correction and color adjust, make a specific profile suitable for just one brand and type of negative |
Scanner softwares often contain several negative profiles based only on color adjust. Gamma correction is defined for each RGB channel along the black and white point. We instead prefer to apply an uniform gamma correction before color level adjust, so we can deal with under-exposed or over-exposed frames just touching a single pre-process parameter. | Scanner softwares often contain several negative profiles based only on color adjust. Gamma correction is defined for each RGB channel along the black and white point. We instead prefer to apply an uniform gamma correction before color level adjust, so we can deal with under-exposed or over-exposed frames just touching a single pre-process parameter. | ||
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</ | </ | ||
- | We choose by visual inspection the best value for gamma. | + | We choose by visual inspection the best value for gamma; 0.007 in this example. |
- | The we open with Gimp a sample photo, we need a shot with a good **black**, **gray** and **white** spots. The process is: | + | Thake a film strip (negated and gamma-corrected with the above recipe) and open it with the Gimp. We need a strip with good **black**, **gray** and **white** spots. The process is: |
- Apply a **pixelize blur filter** on the black, gray and white spots. Make it large enough so you can easly pick the color from it in the next steps. | - Apply a **pixelize blur filter** on the black, gray and white spots. Make it large enough so you can easly pick the color from it in the next steps. | ||
- Open menu **// | - Open menu **// | ||
- From **//All Channels// | - From **//All Channels// | ||
- | - From //Channel// select //Red//, click **//Pick black point//** and click on the black spot. Click **//Pick white point//** and click on the white spot. | + | - From **//Channel//** select |
- Repeat the above step for **// | - Repeat the above step for **// | ||
- | - Annotate | + | - Before closing |
+ | |||
+ | Suppose that the values are: | ||
+ | |||
+ | ^ Channel | ||
+ | | Red | 22 | 1.06 | 193 | | ||
+ | | Green | 20 | 1.01 | 190 | | ||
+ | | Blue | ||
+ | |||
+ | The black and white points are integers 0-255, we need to convert it into a percent value; e.g. for the red white point: 22 / 255 * 100 = 8.63%. | ||
+ | |||
+ | This is the Imagemagick **'' | ||
+ | |||
+ | <code bash> | ||
+ | !/bin/sh | ||
+ | for file in $@; do | ||
+ | convert -colorspace RGB " | ||
+ | -negate \ | ||
+ | -gamma 0.007 \ | ||
+ | -channel R -level 08.63%, | ||
+ | -channel G -level 07.84%, | ||
+ | -channel B -level 11.76%, | ||
+ | " | ||
+ | done | ||
+ | </ | ||
==== Cutting frames using the GIMP ==== | ==== Cutting frames using the GIMP ==== | ||
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- Repeat the last two steps. | - Repeat the last two steps. | ||
+ | |||
+ | ===== ImageMagick convert, memory issue ===== | ||
+ | |||
+ | Executing **convert** on very large images can lead to memory exhausted issue. I experienced it converting a TIF scan into PNG (because I wish to avoid 24 bit Gimp limitation with TIF images): | ||
+ | |||
+ | < | ||
+ | convert very-big.tif very-big.png | ||
+ | convert-im6.q16: | ||
+ | convert-im6.q16: | ||
+ | convert-im6.q16: | ||
+ | </ | ||
+ | |||
+ | It seems that ImageMagick is self-limiting the disk resource it will use, you can fix the configuration file **''/ | ||
+ | |||
+ | <code xml> | ||
+ | < | ||
+ | <policy domain=" | ||
+ | <policy domain=" | ||
+ | <policy domain=" | ||
+ | <policy domain=" | ||
+ | <policy domain=" | ||
+ | <policy domain=" | ||
+ | </ | ||
+ | </ | ||
===== Web references ===== | ===== Web references ===== |
doc/appunti/hardware/canoscan_9000f_mark_ii.txt · Last modified: 2019/12/23 09:36 by niccolo