Canon CR2 large thumbnail

[KingLeonid]

Hi,

I'm trying to use GFL for loading Canon CR2 files. I need to load thumbnail first, then after user clicks on it, load full image.
I faced the following problem with thumbnails for CR2:
If I load embedded thumbnail then it loads very fast but thumbnail is very small. I need larger thumbnail images (256x256 for example) and I know that inside CR2 format there is not only thumbnail + raw sensor full size image, but there is also a large JPEG image - some kind of large preview.
For exmaple in CR2 file with 10Mpix image, there is also 3Mpix jpeg image inside.

Could GFL load that portion of CR2 (IFD #1 Segment) into memory using fast JPEG decoding algorithm?

P.S: I know that some viewers use this segment for displaying CR2 instead of loading raw sensor data.

[KingLeonid]

May be I choose incorrect forum for my question?
Pierre, could you, please, give me an answer to my question.

[xnview]

Could try with gflLoadThumbnail & 0 as w/h size

[KingLeonid]

Thank you for reply.
Now I've got it with LOAD_PARAMS.Flags=0, w=, h=0.
If I set Flags = EMBEDDED_THUMBNAIL then I got small picture, that's also good.

But anyway the loading process of the large preview image is very slow.

I've just compared two tests:
1. Loading larger preview 1953x1301 from CR2 file via LoadThumbnail
2. Loading the same image 1953x1301 from previously saved JPEG file via LoadBitmap

And I could say that loading image from JPEG at least three times faster.
But why?

P.S: According to CR2 spec that I found in the INET, larger preview is also compressed by JPEG algorithm.
PPS: My original size of CR2 is 3906 x 2602.

[xnview]

Please send me a CR2?

[KingLeonid]

I've uploaded zip archive with 2 images - CR2 + JPEG from my test example.
ZIP is 8.6 Mb of size.
Here is the link: http://xnc.jinr.ru/personal/download/canon.zip

Thank you for cooperation.

[xnview]

With your file, i get a embedded thumbnail of 1936x1288, it's quick
Do you use GFL_LOAD_EMBEDDED_THUMBNAIL?

[KingLeonid]

Dear Pierre,
If I use GFL_LOAD_EMBEDDED_THUMBNAIL then I only got very small image 160x120.
Here is the code:

Code: Select all

gflGetDefaultThumbnailParams(&param);
param.Flags |= GFL_LOAD_EMBEDDED_THUMBNAIL;
errcode = gflLoadThumbnail(fname, 0, 0, &ibitmap, &param, 0);

If I do not modify default thumbnail params, then I get large preview but loading is slow.

[xnview]

So send me your email by PM, i'll send new SDK

[KingLeonid]

Dear, Pierre

Thank you for your new version of SDK.
Libgfl290 now works well, and loads large preview very fast.

I really appreciate your early replies and your help in fixing this problem.

[barry]

Dear Pierre!

I have the same problem with loading embedded Thumbnails from RAW-files for Canon PowerShot cameras (with CHDK).

Code: Select all

    lp.Flags := GFL_LOAD_EMBEDDED_THUMBNAIL;
    fGflErrCode := gflLoadThumbnailW(PWideChar( filename ), 0, 0, @gfl_bmp, @lp, finfo);

This code loading a very large thumbnail (1836x1380 px).
You need original RAW-files (.CRW, .DNG)?

[barry]

XnView also build Thumbnail for directory with this RAW-files large time (generate from source image).

[xnview]

yes in RAW you can have big image

[barry]

yes in RAW you can have big image

The original big image I load without problems through gflLoadBitmap. But I mean, if I load the embedded Thumbnail - it is also converted from a large original image, but not extracted from EXIF.