Kia ora anō! I kitea e au tēnei tuhinga, i tuhia i te marama o Mei 2019. He haere tonu tēnei o te raupapa tuhinga mō WAVE me JPEG. Anei Kei roto i tēnei pukapuka ngā mōhiohio e pā ana ki te raupaparorohiko whakawaehere whakaahua me te hōputu whānui.
He paku o te hītori
Kotahi punetēpu o te tuhinga Wikipedia:
Ko te JPEG (Joint Photographic Experts Group) tētahi o ngā hōputu whakairoiro raster rongonui e whakamahia ana mō te penapena whakaahua me ngā whakaahua rite.
I whakawhanakehia tēnei paerewa e te Joint Photographic Experts Group i te tau 1991 hei kōpeketanga whakaahua whai hua.
He aha te ara e haere ai ngā whakaahua mai i te mata ki te JPEG?
Ki tā ētahi he raraunga mata ngā whakaahua JPEG kua kōpeketia mā te whakamahi i te tikanga Huffman, engari kāore tēnei i te pono. He roa te tukanga e pā ana ki ngā raraunga i mua i te kōpeketanga.
Tuatahi, ka hurihia te tauira tae mai i te RGB ki te YCbCr. He rauropi motuhake anō hoki mō tēnei— Kāore a Y e pāngia, nā te mea koia te kawenga mō te kanapa, ā, ka kitea tōna huringa.
Ko tā rātou mahi tuatahi ki te whakaahua ko te whakangawari (tātaritanga iti). He māmā noa iho te mārama: tangohia he huinga pika 2x2, kātahi ka tangohia ko Cb me Cr—ko ngā uara toharite o ia wāhanga YCbCr o ēnei pika e 4. Nō reira, i toa mātou i te 6 paita, hei utu mō te 4 Y, 4 Cb, 4 Cr, i whiwhi mātou i te 4 Y me te Cb me te Cr kotahi mō ia o rātou (4 + 4 + 4 = 12; 4 + 1 + 1 = 6; 12 - 6 = 6). I ngā tauine 2x2 ōrite, he mea whakamiharo te kōpeketanga ngaronga me te ōwehenga āhua o te 2:1. Ka pā tēnei ki te ahua katoa. Nō reira, kua haurua te rahi. Ā, ka taea e tātou te whakamahi i tēnei tikanga nā tō tātou tirohanga tae. Ka taea e te tangata te kite ngāwari i te rerekētanga o te kanapa, engari kāore i te tae mēnā ka toharitehia ki runga i tētahi poraka iti o ngā pika. Ka taea hoki te mahi whakaitiiti i roto i te rārangi, 4 pika whakapae me te poutū. Ko te kōwhiringa tuatahi ka whakamahia pinepine ake. Mena he mea nui te kounga o te ahua, kāore e mahia te whakaitiiti i te katoa.
He whakaahua ā-kanohi o te angiangi (kāore a Habr i whakaae kia whakaurua he GIF)
Ko te wāhanga matua o te whakarite
DCT
Nā, ko te wāhanga tino uaua, tino tika hoki tēnei. Ka wehea te ahua katoa ki ngā poraka 8x8 (ka whakamahia he whakakīkī mēnā ehara te taumira i te tauwehenga o te rahi poraka).
Tāpirihia ki ia poraka inaianei DCT (Whakawhitinga Kōhinu Momotu)I tēnei wāhanga, ka tangohia ngā huānga kore e hiahiatia ana mai i te ahua. Mā te whakamahi i te DCT, me whakatau tātou mēnā he wāhanga hoha o te ahua kei roto i tētahi poraka (8x8): te rangi, te pakitara; mēnā rānei he hanganga uaua kei roto (te makawe, ngā tohu, me ētahi atu). He mea tika kia taea te whakaahua i ngā pika 64 tae rite mā te kotahi noa iho, nā te mea kua mōhiotia kētia te rahi o te poraka. Koinei te ōwehenga kōpeketanga: 64 ki te 1.
Ka hurihia e te DCT te poraka hei whānuitanga, ā, ki te huri tere ngā pānui, ka pai ake te tauwehenga, ā, ki te koi ake te whakawhiti, ka teitei ake te putanga. Ki te teitei ake te tauwehenga, ka whakaatu te ahua i ngā whakawhiti tae me te kanapa mārama; ki te iti ake, ka kitea ngā huringa ngawari (maeneene) o ngā uara o ngā wāhanga YCbCr i roto i te poraka.
Te inenga
Ka whakamahia ngā tautuhinga kōpeketanga ki konei. Ka wehea ia tauwehenga i roto i ia matihiko 8x8 e tētahi tau motuhake. Ki te kore koe e hiahia ki te whakaiti i te kounga o te ahua i muri i ngā whakarerekētanga katoa, me kotahi te wehewehe. Ki te mea he mea nui ake ki a koe te tapuwae mahara o te whakaahua, ka nui ake te wehewehe i te kotahi, ā, ka whakaawhiwhihia te wāhanga. Ko te tikanga o tēnei, he maha ngā kore ka puta mai i te whakaawhiwhi.
Ka whakamahia te ine ine hei whakahohe i te kōpeketanga nui ake. Koinei te āhua o tēnei mā te whakamahi i te kauwhata ine ine y = sin(x):
Kōpeketanga
Tuatahi, ka haere tātou i roto i te matihiko i roto i te tauira zig-zag:
Ka whiwhi tātou i tētahi huinga tau kotahi-ahu. Ka kite tātou he maha ngā kore kei roto, ka taea te tango. Hei mahi i tēnei, hei utu mō te raupapa o ngā kore maha, ka tuhia e tātou he kore kotahi, ā, ka whai mai he tau e tohu ana i tō rātou tau i roto i te raupapa. Mā tēnei, ka taea e tātou te whakaiti i te rahi o te huinga katoa ki te 1/3. Kātahi ka kōpeke noa i tēnei huinga mā te whakamahi i te tikanga Huffman, ka tuhia ki te kōnae tonu.
Ka whakamahia te waahi
I ngā wāhi katoa. Pērā i te PNG, ka whakamahia te JPEG i roto i ngā kāmera, i ngā pūnaha whakahaere (hei tohu kamupene, hei ata taupānga, hei whakaahua iti), me ngā wāhi katoa e tika ana kia rongoatia pai ai ngā whakaahua.
mutunga
I tēnei wā, ko te mōhiotanga ki te JPEG he mea nui mō ngā kaupapa mātauranga anake, nā te mea kua whakauruhia ki roto i ngā mea katoa, ā, kua arotauhia hoki e ngā rōpū nui o te tangata, engari he reka tonu te pūtaiao.
Rauemi
Source: will.com
