I'm sorry for I did not express my current situation well enough for you to understand my intention: Images taken by a certain manufacturer's phone/camera have their own fixed compression algorithms. I hope to simulate these compression algorithms to generate my own images, whether they are input images or self-generated ones. This issue has been bothering me for a long time, and I have not been able to find a solution
在2023年6月29日星期四 UTC+8 05:20:05<Hugh Shaw> 写道： > What if I rephrase the question: Is there a way for me to compress a plain > red image using the same compression method as reference.jpg using > libjpeg-turbo? The resulting red image should have the exact same hex code > between FFD8 and FFDA as reference.jpg. > > 在2023年6月29日星期四 UTC+8 04:56:28<DRC> 写道： > >> Even if you use the identical compression method, there is no way to >> perfectly simulate a JPEG reference image unless you can obtain the >> original pixels that were used to generate the reference image. The term >> "re-compress" means that you have to decompress first, so you will incur >> generational loss, as I mentioned below. You can't perfectly duplicate the >> JPEG image data (the data after the SOS marker) from the metadata and >> decompressed pixels of a reference JPEG image. You can perfectly duplicate >> the JPEG image data from the metadata of a reference JPEG image if you have >> access to the original pixels that were used to generate the reference >> image, but your messages imply that you don't. That means that what you're >> trying to do is impossible. >> On 6/28/23 4:46 PM, Hugh Shaw wrote: >> >> I think you may have misunderstood my intention. What I hope to achieve >> is to compress an image using the same compression method as reference.jpg, >> perfectly simulating it. In my understanding, the hex code of a JPEG >> includes information such as DQT, SOF, and DHT. I wonder if I can use this >> information to re-compress an image and generate output.jpg. Theoretically, >> the hex code between FFD8 and FFDA should be identical in output.jpg and >> reference.jpg, and the compression data after SOS should also be calculated >> based on information such as DQT, SOF, and DHT. I hope to use libjpeg-turbo >> to implement this function. It seems that jpegtran cannot achieve this. >> >> >> 在2023年6月29日星期四 UTC+8 04:19:58<DRC> 写道： >> >>> I can only barely comprehend what you are trying to do or why, but >>> unless the reference image is a lossless JPEG (I assume not, if it has a >>> DQT), any decompression/compression cycle will result in generational >>> loss. Thus, you cannot exactly regenerate a lossy reference JPEG image >>> unless you have the original uncompressed image that was used to generate >>> the reference image in the first place. Once a JPEG image is generated, >>> then some of that original data is lost. The best you can do is copy the >>> DCT blocks (in the frequency domain) from one JPEG container to another, >>> which is what jpegtran does. That avoids a decompression/recompression >>> cycle and thus avoids generational loss, so the transformed JPEG image has >>> no additional loss relative to the reference JPEG image. However, there >>> are limits to what you can do in the frequency domain. You can reorder the >>> DCT blocks; spatially transpose, rotate, or flip the blocks; remove or >>> change the order of some of the component planes (e.g. convert color to >>> grayscale); negate the coefficients (photo negative); re-quantize the >>> coefficients (lower the effective JPEG quality); change the entropy >>> algorithm (e.g. convert baseline to progressive or arithmetic); add restart >>> markers; crop the image (by discarding certain blocks); wipe an image >>> region (by greying out certain blocks); drop another image into the source >>> image (by replacing certain blocks); or remove metadata. >>> On 6/28/23 3:59 PM, Hugh Shaw wrote: >>> >>> I have a specific requirement I need help with and hope to get >>> assistance from experts in the field. I have learned that for the same >>> compression algorithm, the compression fingerprints are consistent. This >>> means that the data from FF D8 to just before the scan line FF DA are >>> always identical. Based on this information, I would like to be able to >>> duplicate the compression fingerprint of one image and apply it to another. >>> >>> Specifically, I need to accomplish two things: >>> >>> First, use the perfectly compressed fingerprint from reference.jpg to >>> compress input.jpg and generate output.jpg. Second, make sure that the DQT, >>> SOF, and DHT information in output.jpg is exactly the same (including hex >>> codes) as in reference.jpg. I have already ensured that the pixel >>> dimensions of input.jpg and reference.jpg are the same. >>> >>> I have attempted to code a solution, as shown below, which involves >>> manually copying the quantization and Huffman tables, copying critical >>> parameters, and applying the compression and decompression. However, the >>> resulting output.jpg differs in hex code from the reference image, even >>> though the dimensions are the same. >>> >>> *Due to lenght limitations, I can only include the code I tried in the >>> attachment* >>> >>> I am unsure what the issue is and would appreciate any guidance in >>> resolving this problem. Thank you. >>> >>> Looking forward to your reply! >>> Best regards, >>> >>> -- >>> You received this message because you are subscribed to the Google >>> Groups "libjpeg-turbo User Discussion/Support" group. >>> To unsubscribe from this group and stop receiving emails from it, send >>> an email to libjpeg-turbo-u...@googlegroups.com. >>> To view this discussion on the web visit >>> https://groups.google.com/d/msgid/libjpeg-turbo-users/db388722-522d-40f7-b868-185684060ffan%40googlegroups.com >>> >>> <https://groups.google.com/d/msgid/libjpeg-turbo-users/db388722-522d-40f7-b868-185684060ffan%40googlegroups.com?utm_medium=email&utm_source=footer> >>> . >>> >>> -- >> You received this message because you are subscribed to the Google Groups >> "libjpeg-turbo User Discussion/Support" group. >> To unsubscribe from this group and stop receiving emails from it, send an >> email to libjpeg-turbo-u...@googlegroups.com. >> >> To view this discussion on the web visit >> https://groups.google.com/d/msgid/libjpeg-turbo-users/384ceb0a-e840-4bb9-b94c-1a613f965231n%40googlegroups.com >> >> <https://groups.google.com/d/msgid/libjpeg-turbo-users/384ceb0a-e840-4bb9-b94c-1a613f965231n%40googlegroups.com?utm_medium=email&utm_source=footer> >> . >> >> -- You received this message because you are subscribed to the Google Groups "libjpeg-turbo User Discussion/Support" group. 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