Image overlay (NOT edge overlay) - Feature Requests - CHDK Forum
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Image overlay (NOT edge overlay)

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Offline animaux

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Image overlay (NOT edge overlay)
« on: 08 / June / 2011, 15:26:06 »
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Some time ago Stimpy wrote:

Quote
I would love the ability to choose any photo from my SD card library & overlay this image with 50% opacity onto the viewfinder screen.

I would need exactly this functionality for images on this page: http://zeitsprung.animaux.de/

It would be even better width adjustable opacity, plus the possibility to scale the image (centered). (An additional option to display the overlay in grayscale would be great too)
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Offline mastodon

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Re: Image overlay (NOT edge overlay)
« Reply #1 on: 09 / June / 2011, 02:57:53 »
Would be a bloody good feature! :)
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Offline a1ex

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Re: Image overlay (NOT edge overlay)
« Reply #2 on: 09 / June / 2011, 05:12:21 »
A simple trick to emulate 50% transparency is to draw only half of overlay pixels. Also, for this feature I think it's enough to use grayscale. I'm not sure what colors are available for the bitmap overlay in CHDK, but on DSLRs there are around 40 gray shades always there.

My implementation (on 550D/60D Magic Lantern) "copies" the luma channel from YUV422 image buffer to BMP overlay; only the pixels where (i+j)%2 == 0 are changed. A copy of overlay is saved to card, due to memory constraints (and it's read every time the overlay needs refreshing). Not very elegant, but works.

This feature was actually inspired somehow from CHDK's edge overlay.
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Offline Televerket

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Re: Image overlay (NOT edge overlay)
« Reply #3 on: 07 / August / 2011, 05:49:56 »
Quote from: mastodon on 09 / June / 2011, 02:57:53
Would be a bloody good feature! :)
Indeed!

I like shooting season-comparing-photos and a feature like the one described would make that a great deal easier.
http://img683.imageshack.us/img683/4427/allignerade2.jpg
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Offline Televerket

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Re: Image overlay (NOT edge overlay)
« Reply #4 on: 25 / September / 2011, 06:59:43 »
Is no one else interested in this feature? I would be so happy if it was developed and enabled in CHDK.
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Offline msl

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Re: Image overlay (NOT edge overlay)
« Reply #5 on: 25 / September / 2011, 12:09:17 »
Have you already tried the RAW development features? With this functions you can merge RAW files. Maybe this is a first step for this feature request.

http://chdk.wikia.com/wiki/CHDK_firmware_usage/AllBest#Miscellaneous_Stuff_.3E_File_Browser_.3E_RAW_Merge
http://chdk.wikia.com/wiki/Lua/Lua_Reference#RAW_development

msl
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Offline waterwingz

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Re: Image overlay (NOT edge overlay)
« Reply #6 on: 25 / September / 2011, 12:24:18 »
Quote from: msl on 25 / September / 2011, 12:09:17
Have you already tried the RAW development features? With this functions you can merge RAW files. Maybe this is a first step for this feature request.

@msl :  If I understand the original post correctly,  the request isn't for a method of combining images.  What he wants is a way to put a semi-transparent version of an original jpg image from the SD card onto the camera LCD while in shooting mode so that you can exactly line up a new photo - maybe months after the original photo was taken.   Sort of like the existing save & load edge overlay function but more precise.  And not requiring you to remember to save the edge overlay in the first place.

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Offline a1ex

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Re: Image overlay (NOT edge overlay)
« Reply #7 on: 25 / September / 2011, 13:01:43 »
I don't know about the compacts, but the dSLRs reuse the LiveView image buffer in playback mode (so the overlay can be created from an existing JPEG with the same code used for LiveView).

I've implemented a function for comparing two images in playback mode like this (on dSLRs):


But Televerket's link just gave me another idea :)
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Offline waterwingz

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Re: Image overlay (NOT edge overlay)
« Reply #8 on: 25 / September / 2011, 13:33:08 »
I'm not sure how hard it would be to decode a jpg onto the LCD image buffer so that it looks exactly like the LCD image did when the picture was taken.  Might be a lot easier to just add a mode where CHDK saves the LCD image buffer in a seperate file with the same name but different extension as the original image.  Reloading that and displaying it 50% transparent or in a gray scale would not be that hard by comparision and alignment should be exact.
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Offline msl

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Re: Image overlay (NOT edge overlay)
« Reply #9 on: 25 / September / 2011, 16:43:52 »
Quote from: waterwingz on 25 / September / 2011, 12:24:18
What he wants is a way to put a semi-transparent version of an original jpg image from the SD card onto the camera LCD while in shooting mode so that you can exactly line up a new photo - maybe months after the original photo was taken.

Ok, the RAW development was the wrong approach. But an overlay picture with variable opacity should not be generated from a JPG . This needs many computing power for decoding. Saving the LCD image buffer is a good way.

msl
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