Odd question about Image Thumbnails vs the actual content of the image.

Dark_Angel · 6 Jun 2009 at 16:40

Ok basic story, I have a few images in a folder filled with a large amounts of images that really are confusing me with their behavior.

Basically most of the images in this folder are color, apart from a few. Now this obviously means those images are black and white. Simple so far right?

Ok, when windows is loading the thumbnails for the images though (especially if I scroll down the images fast in the folder) until I reach these black and white images, just for a second the thumbnail is full color. What the heck is going on there? it then goes back to the BLack and White thumbnail? the image format is .jpg.

whitecrook · 6 Jun 2009 at 18:40

well if an image is not colour that does not 'obvioulsy' mean it's black and white.

Second, there's no such thing as a black and white JPEG. It will be 24bpp colour or very rarely 8bpp greyscale. If you really do have a black and white jpeg I would be very interested in seeing the specific file in fo.

Also, jpegs file support embedded thumbnails so the image in the thumbnail does not nessecarily match the image data in the rest of the file.

Dark_Angel · 6 Jun 2009 at 19:13

whitecrook said:
well if an image is not colour that does not 'obvioulsy' mean it's black and white.

Second, there's no such thing as a black and white JPEG. It will be 24bpp colour or very rarely 8bpp greyscale. If you really do have a black and white jpeg I would be very interested in seeing the specific file in fo.

Also, jpegs file support embedded thumbnails so the image in the thumbnail does not nessecarily match the image data in the rest of the file.

The file can be black and white and JPEG. it just means that the file is black and white and saved in the JPG format, (google black and white jpeg for an example of what I mean).

I kind of figured that the file's color thumbnail must have an embedded, however I am curious to why only this file is doing it. Still, I suppose it is just a quirk.

As for the grey scale, I just used the term black and white - which is the standard term for when someone is describing a photo, for example photoshops command to turn an image in to a greyscale is actually called Black and White from within the program itself.

Also deke mcclelland, who is a well known Photoshop expert (adobe certified and has lectured) as well as adobe themself regularly call a JPEG file a black and white

(this of course, assumes the photo is only black and white).

The file format isn't important if describing a photo as colour or black and white, however I mentioned the file type because of the thumbnail behavior.

whitecrook · 6 Jun 2009 at 19:29

Dark_Angel said:
The file can be black and white and JPEG. it just means that the file is black and white and saved in the JPG format

A photo can be black and white. A JPEG file can not be. A black and white photo can be saved as a JPEG, but although it is a black and white photo, the JPEG file will still be 24bpp (i.e. not black and white) Black and white is 1 bpp. i.e. either black or white.

What you probably want is to rebuild your thumbnails. I know ACDSee can do this. Ifranview probably can as well.

Dark_Angel · 6 Jun 2009 at 19:33

whitecrook said:
A photo can be black and white. A JPEG file can not be. A black and white photo can be saved as a JPEG, but although it is a black and white photo, the JPEG file will still be 24bpp (i.e. not black and white) Black and white is 1 bpp. i.e. either black or white.

What you probably want is to rebuild your thumbnails. I know ACDSee can do this. Ifranview probably can as well.

.... I think you are reading in to this a bit to far, or not reading between the lines or we are mis communicating or something

Obviously the file when it was taken the image was color , and ran a few special effects filters on the original image, and then converted it in to a B/W JPEG image (with the RGB color channels obviously).

I was just curious to why only those couple of thumbs was acting weird (in other words obviously showing the un-altered, unconverted file) rather than the colour one

I will check out that program though

whitecrook · 6 Jun 2009 at 19:44

because the thumbs were generated and saved into the file when the file was created i.e. when it was still a colour file. You need to update the thumbs with a new version of the picture. In fact I'm pretty sure some photohop literally has an option for 'update embedded thumb' or something when saving. Maybe that's in Iview_32 as well...

Dark_Angel · 6 Jun 2009 at 19:47

Kinda figured, just wanted to make sure.

Annoying as hell though that they didn't leave the photo's how they was, they would have been a lot cooler :/

whitecrook · 6 Jun 2009 at 19:59

Original: 24bpp : 45169 unique colours 48K disk/1.29MB uncompressed

1 bpp saved as PNG (which supports black and white images, 1bpp): 1bpp 2 colours, 2 unique colours. 14KB disk, 56K uncompressed.

saved as 8bpp JPG at 100%: no. of colours 256. unique colours 4. 152KB disk and 441 uncompressed. Saving it at 70% gives 83 unique colours....

I now know you are talking about a black and white 'photo' as opposed to a black and white image file, but that wasn't clear at the start. I hope these pictures show your where I was coming from...

Dark_Angel · 6 Jun 2009 at 20:49

I understood what you meant, but I thought I was being clear enough

Guess not, oh well.

Rozzy85 · 6 Jun 2009 at 22:22

Have you tried deleting thumbs.db from the folder the photos are in? Once you've deleted it Windows will re-generate the thumb images again. If you can't see it you need to disable "Hide protected operating system files" in folder options.