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#1
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Deconstruct a GIF file
Can someone deconstruct a GIF screenshot that I have edited to remove
information? If I successively edit a GIF screenshot to remove private data and then post the resulting GIF file on the net, is there something I should do to test whether the data I removed is not still stuck in hidden "layers" in the GIF file? |
#2
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Deconstruct a GIF file
On 6/5/2017 1:27 AM, Chaya Eve wrote:
Can someone deconstruct a GIF screenshot that I have edited to remove information? If I successively edit a GIF screenshot to remove private data and then post the resulting GIF file on the net, is there something I should do to test whether the data I removed is not still stuck in hidden "layers" in the GIF file? Very easy: open the file in a binary editor and check for the data you removed. If you don't see it, it's gone. -- best regards, Neil |
#3
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Deconstruct a GIF file
"Chaya Eve" wrote
| Can someone deconstruct a GIF screenshot that I have edited to remove | information? | GIF doesn't usually have metadata. Is that what you mean? You can look up the file format. Aside from the file signature and actual image data, it's mainly color map data that details the colors. Since GIF can only have 256 colors, those colors have to be specified. There can be a text-based comment section, but I don't think it's typically used. It's more like the possibility is provided by the format. The only issue I can think of is that if you have a sleazy image editor. (Like Photoshop.) Some companies like Adobe like to toot their own horn and essentially put advertising in the header. You can check for that with a hex editor. But I doubt even Adobe will do that with GIFs. In general, if you're not sure, you can save an image as a bitmap (BMP), then open that and save it as your final image format. A BMP consists of nothing more than a short file header that specifies width, height, color depth, etc, followed by the actual image bytes. It's also a good way to work on images that you want to save in another format later. When you save a JPG you lose data. When you save a GIF you limit and corrupt the colors. So those transitions should only be done after any image editing is finished. Presumably your screenshot started out as a BMP. If not, it should. (PrtScr then paste will give you a plain bitmap.) |
#4
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Deconstruct a GIF file
On 05/06/2017 12:34, Mayayana wrote:
"Chaya Eve" wrote | Can someone deconstruct a GIF screenshot that I have edited to remove | information? | GIF doesn't usually have metadata. Is that what you mean? You can look up the file format. Aside from the file signature and actual image data, it's mainly color map data that details the colors. Since GIF can only have 256 colors, those colors have to be specified. There can be a text-based comment section, but I don't think it's typically used. It's more like the possibility is provided by the format. The only issue I can think of is that if you have a sleazy image editor. (Like Photoshop.) Some companies like Adobe like to toot their own horn and essentially put advertising in the header. You can check for that with a hex editor. But I doubt even Adobe will do that with GIFs. In general, if you're not sure, you can save an image as a bitmap (BMP), then open that and save it as your final image format. A BMP consists of nothing more than a short file header that specifies width, height, color depth, etc, followed by the actual image bytes. It's also a good way to work on images that you want to save in another format later. When you save a JPG you lose data. When you save a GIF you limit and corrupt the colors. So those transitions should only be done after any image editing is finished. Presumably your screenshot started out as a BMP. If not, it should. (PrtScr then paste will give you a plain bitmap.) cough It's none of MY business, but I find things like this very interesting! Thanks for sharing your knowledge. :-) As an aside, Mayayana, if you've a few minutes spare, I'd welcome your views on THIS post I've made:- Message-ID: TIA -- "Do something wonderful, people may imitate it." |
#5
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Deconstruct a GIF file
In article , Mayayana
wrote: The only issue I can think of is that if you have a sleazy image editor. (Like Photoshop.) Some companies like Adobe like to toot their own horn and essentially put advertising in the header. You can check for that with a hex editor. But I doubt even Adobe will do that with GIFs. nonsense. nobody puts ads in file headers, nor is photoshop sleazy. In general, if you're not sure, you can save an image as a bitmap (BMP), then open that and save it as your final image format. A BMP consists of nothing more than a short file header that specifies width, height, color depth, etc, followed by the actual image bytes. It's also a good way to work on images that you want to save in another format later. no it isn't. bmp is a horrible choice. When you save a JPG you lose data. When you save a GIF you limit and corrupt the colors. So those transitions should only be done after any image editing is finished. Presumably your screenshot started out as a BMP. If not, it should. (PrtScr then paste will give you a plain bitmap.) bmp is very, very rarely used anymore. |
#6
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Deconstruct a GIF file
On Mon, 5 Jun 2017 07:34:14 -0400, Mayayana
wrote: GIF doesn't usually have metadata. I use GIF because it doesn't have EXIF metadata! Is that what you mean? I'm not asking about meta data. I'm asking about layers. I often start with a PNG which has layers, and I edit the PNG which has more layers and then I save to GIF because I'm trying to get rid of the layers that I edited out. When you save a JPG you lose data. When you save a GIF you limit and corrupt the colors. So those transitions should only be done after any image editing is finished. Presumably your screenshot started out as a BMP. If not, it should. They generally start out as PNG files, which have layers which is why I want to save to some other format which will lose those layers. I just don't want to accidentally send out information in layers that I thought I deleted when I cut out sections of a screenshot. |
#7
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Deconstruct a GIF file
On 2017-06-05 15:33:45 +0000, Chaya Eve said:
On Mon, 5 Jun 2017 07:34:14 -0400, Mayayana wrote: GIF doesn't usually have metadata. I use GIF because it doesn't have EXIF metadata! That isn't the only thing GIFs don't have. Is that what you mean? I'm not asking about meta data. I'm asking about layers. I often start with a PNG which has layers, and I edit the PNG which has more layers and then I save to GIF because I'm trying to get rid of the layers that I edited out. I guess these are not animated GIFs. When you save a JPG you lose data. When you save a GIF you limit and corrupt the colors. So those transitions should only be done after any image editing is finished. Presumably your screenshot started out as a BMP. If not, it should. They generally start out as PNG files, which have layers which is why I want to save to some other format which will lose those layers. Only if they are created with layers. If they are as you claim, just screenshots, there is no reason for the layers to exist. If they are images you have lifted illicitly, that is a different issue. I just don't want to accidentally send out information in layers that I thought I deleted when I cut out sections of a screenshot. You are waaay too paranoid. Especially if all you are doing is dealing with PNG screenshots. -- Regards, Savageduck |
#8
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Deconstruct a GIF file
On 2017-06-05 11:33, Chaya Eve wrote:
I just don't want to accidentally send out information in layers that I thought I deleted when I cut out sections of a screenshot. In Photoshop one could easily "flatten" the image in the layers command (you end up with a sole layer) and then save it to any format including ..png. Then use exiftool to verify and/or remove any (all) metadata that may be left in there. The "all" removal command. exiftool =all- filename -- "If war is God's way of teaching Americans geography, then recession is His way of teaching everyone a little economics." ..Raj Patel, The Value of Nothing. |
#9
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Deconstruct a GIF file
"nospam" wrote
| bmp is very, very rarely used anymore. Of course not, on Macs. The OP seems to be on Windows. A BMP is the most basic bitmap format. A grid of pixel values. It's what *all* raster graphics are. JPG, PNG, GIF, etc all render as bitmaps. Only the storage varies. A BMP file is only that grid of pixel values, with a very minimal file header of something like 22 bytes. The image you work on in Photoshop is a bitmap. Most of the filters you can use in Photoshop are essentially math formulas applied to that bitmap. So on Windows, the only sensible way to work with non-RAW is as BMP, or as TIF if one prefers it compressed. But in that case a TIF is only a compressed BMP. One could work with PNGs, but there's not much point. If one works in JPG then each save is lossy. If one works in GIF then the number of colors has been severely limited. There are different ways to go to 8-bit color from 24-bit. Getting the best GIF can sometimes take a few tries. So there's no sense reduing from BMP until editing is done and one wants a finished copy as GIF. |
#10
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Deconstruct a GIF file
"Chaya Eve" wrote
| I'm not asking about meta data. | I'm asking about layers. | Layers? Are you sure you're not talking about layers in the graphic editor? Once you save a file to disk you're merging layers. The end result is essentially a bitmap. I don't know of any format that stores layers, except the custom formats used by things like Paint Shop Pro or Photoshop that retain info about your editing. But those are temp formats that other people usually can't open. If you save to GIF then you're reducing from 24-bit color to 8-bit. (16 million+ colors to 256 colors.) The only reason to use GIF is for simple images, especially online when a small file size is important. |
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